Kamiel Spoelstra

Dr. ir. Kamiel Spoelstra

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Visiting Address

Droevendaalsesteeg 10
6708 PB Wageningen

+31 (0) 317 47 34 00

The Netherlands



Nocturnal illumination causes habitat loss, and changes the temporal and spatial organization of activity for many species. Research on how light affects plants and animals and their interaction is essential to reduce impact.


Dr. Ir. Kamiel Spoelstra works on the presence and activity of species: what is our influence on how species organize their activity? And how do animals change the organization of their activity as a result of human disturbance – do species occupy different niches, in time and place? How do possible changes affect species’ populations, and how do they interact? His drive is to visualize the invisible in ecosystems: hidden effects, latent processes, secretive behaviour by inconspicuous species.

He graduated at the University of Groningen in 2005, and continued there with a post-doc position (2005-2007), followed by post-docs at Princeton University (2007-2009), Max Planck Institute for Ornithology (2009-2010), and Netherlands Institute of Ecology (NIOO-KANW, 2011-2019). He currently has a research position there.

Currently, his main project is about the impact of light pollution for which he maintains a large-scale setup with experimental illumination of forest-edge habitat, studying the impact of the spectral composition of light, and light intensity on several species groups. For more information on this project, please check www.lichtopnatuur.org.

Research groups


Ancillary activities


Peer-reviewed publications

  • Science of the Total Environment

    Artificial light at night drives diel activity patterns of synanthropic pipistrelle bats and their prey

    Claire Hermans, Iryna Litovska, Mélyssa De Pastors, Marcel E. Visser, Kamiel Spoelstra
    The use of artificial light at night (ALAN) has increased drastically worldwide over the last decades. ALAN can have major effects on nocturnal communities, including insects and bats. Insects are attracted to street lights and few bat species take advantage of this by foraging on the attracted insects. ALAN potentially affects the temporal patterns of insect abundance and thereby bat foraging behaviour. In a natural dark environment, these patterns are usually bimodal, with an activity peak in the early evening and the morning. Little is known about how ALAN affects insect presence throughout the night, and whether the light spectrum plays a role. This is important, as these temporal changes may be a key driver of disturbances in bat-insect interactions. Here, we studied how white and red light affect insects' and bats' nightly activity patterns. The activity of insects and bats (Pipistrellus spp.) was recorded throughout the night at seven experimentally illuminated sites in a forest-edge ecosystem. ALAN disrupted activity patterns, with both insects and bats being more active throughout the night. ALAN facilitated all-night foraging in bats especially near white light, but these effects were attenuated near red light. The ability to forage throughout the night may be a key advantage causing synanthropic bats to dominate in illuminated environments, but this could also prove detrimental in the long term. As red light reduced disturbing effects of ALAN on insects and bats diel activity pattern, it opens the possibility of using spectral composition as a mitigation measure.
  • Philosophical transactions of the Royal Society of London. Series B, Biological sciences

    Long-term exposure to experimental light affects the ground-dwelling invertebrate community, independent of light spectra

    Kamiel Spoelstra, Sven Teurlincx, Matthijs Courbois, Zoë M. Hopkins, Marcel E. Visser, Therésa M. Jones, Gareth R. Hopkins

    Our planet endures a progressive increase in artificial light at night (ALAN), which affects virtually all species, and thereby biodiversity. Mitigation strategies include reducing its intensity and duration, and the adjustment of light spectrum using modern light emitting diode (LED) light sources. Here, we studied ground-dwelling invertebrate (predominantly insects, arachnids, molluscs, millipedes, woodlice and worms) diversity and community composition after 3 or 4 years of continued nightly exposure (every night from sunset to sunrise) to experimental ALAN with three different spectra (white-, and green- and red-dominated light), as well as for a dark control, in natural forest-edge habitat. Diversity of pitfall-trapped ground-dwelling invertebrates, and the local contribution to beta diversity, did not differ between the dark control and illuminated sites, or between the different spectra. The invertebrate community composition, however, was significantly affected by the presence of light. Keeping lights off during single nights did show an immediate effect on the composition of trapped invertebrates compared to illuminated nights. These effects of light on species composition may impact ecosystems by cascading effects across the food web. This article is part of the theme issue 'Light pollution in complex ecological systems'.

  • Science

    Effects of anthropogenic light on species and ecosystems

    Annika K. Jägerbrand, Kamiel Spoelstra
    Anthropogenic light is ubiquitous in areas where humans are present and is showing a progressive increase worldwide. This has far-reaching consequences for most species and their ecosystems. The effects of anthropogenic light on natural ecosystems are highly variable and complex. Many species suffer from adverse effects and often respond in a highly specific manner. Ostensibly surveyable effects such as attraction and deterrence become complicated because these can depend on the type of behavior and specific locations. Here, we considered how solutions and new technologies could reduce the adverse effects of anthropogenic light. A simple solution to reducing and mitigating the ecological effects of anthropogenic light seems unattainable, because frugal lighting practices and turning off lights may be necessary to eliminate them.
  • Proceedings of the Royal Society B: Biological Sciences

    Ingrained city rhythms

    Barbara Tomotani, Fabian Timpen, Kamiel Spoelstra
    Urbanization dramatically increases the amount of light at night which may disrupt avian circadian organization. We measured activity patterns of great tits breeding in the city and forest, and subsequently measured two clock properties of these birds under controlled conditions: tau (endogenous circadian clock speed) and after-effects (history-dependency of the clock relative to previous conditions). City and forest birds showed a high repeatability of activity onset (0.60 and 0.41, respectively), with no difference between habitats after controlling for date effects. Activity duration and offset showed more variance, without a difference between birds from the two habitats. Tau did not differ between city and forest birds, however, city birds showed stronger after-effects, taking more days to revert to their endogenous circadian period. Finally, onset of activity was correlated with clocks speed in both habitats. Our results suggest that potential differences in activity timing of city birds is not caused by different clock speeds, but by a direct response to light. Persistence in after-effects suggests a reduced sensitivity of the clock to light at night. Urbanization may select for clock properties that increase the inertia of the endogenous circadian system to improve accuracy of activity rhythms when exposed to noisier lighting cues.
  • Movement Ecology

    Combining acoustic tracking and LiDAR to study bat flight behaviour in three-dimensional space

    Claire Hermans, Jens koblitz, Harm Bartholomeus, Peter Stilz, Marcel E. Visser, Kamiel Spoelstra
    Background: Habitat structure strongly influences niche differentiation, facilitates predator avoidance, and drives
    species-specific foraging strategies of bats. Vegetation structure is also a strong driver of echolocation call character-
    istics. The fine-scale assessment of how bats utilise such structures in their natural habitat is instrumental in under-
    standing how habitat composition shapes flight- and acoustic behaviour. However, it is notoriously difficult to study
    their species-habitat relationship in situ.
    Methods: Here, we describe a methodology combining Light Detection and Ranging (LiDAR) to characterise three-
    dimensional vegetation structure and acoustic tracking to map bat behaviour. This makes it possible to study fine-
    scale use of habitat by bats, which is essential to understand spatial niche segregation in bats. Bats were acoustically
    tracked with microphone arrays and bat calls were classified to bat guild using automated identification. We did this
    in multiple LiDAR scanned vegetation plots in forest edge habitat. The datasets were spatially aligned to calculate the
    distance between bats’ positions and vegetation structures.
    Results: Our results are a proof of concept of combining LiDAR with acoustic tracking. Although it entails challenges
    with combining mass-volumes of fine-scale bat movements and vegetation information, we show the feasibility and
    potential of combining those two methods through two case studies. The first one shows stereotyped flight patterns
    of pipistrelles around tree trunks, while the second one presents the distance that bats keep to the vegetation in the
    presence of artificial light.
    Conclusion: By combining bat guild specific spatial behaviour with precise information on vegetation structure, the
    bat guild specific response to habitat characteristics can be studied in great detail. This opens up the possibility to
    address yet unanswered questions on bat behaviour, such as niche segregation or response to abiotic factors in inter-
    action with natural vegetation. This combination of techniques can also pave the way for other applications linking
    movement patterns of other vocalizing animals and 3D space reconstruction.
  • Animal Conservation

    Manipulating spectra of artificial light affects movement patterns of bats along ecological corridors

    Kévin Barré, I. Thomas, Isabelle Le Viol, Kamiel Spoelstra, Christian Kerbiriou
    Animal movement throughout the landscape is a key concept for population viability. Human footprint can reduce animal movement through barrier effects such as habitat change and fragmentation, or through enhanced resources. Artificial light at night (ALAN) can affect the movement of nocturnal animals such as bats that are highly mobile in the landscape. Very few studies have explicitly quantified the choices that moving bats make when they encounter a light source on their flight routes. We assessed whether ALAN of different colours (green, red and white) compared to control conditions affected the use of ecological corridors, considering (i) activity and (ii) movement along the corridor, for open, edge (i.e. light-opportunistic) and narrow-space (i.e. light-averse) foraging bats. We modelled the effects of 28 independent lampposts at four experimental sites on bat activity and movement (i.e. the number of trajectories towards the lamppost and the probability of lamppost crossing). Each lamppost was sampled two to three times over eight complete nights using paired passive acoustic stereo recorders to record bat activity and reconstruct bat trajectories. Narrow-space foragers were much less active in presence of any light source, and fewer flew towards any lit lampposts. Open and edge-space foragers were more active close to white and green lights, and to a lesser extent red light, compared to unlit control sites. Edge-space foragers overall flew more towards white and green lampposts, but had a lower probability of fully crossing a white and red-lighted site. The study shows that ALAN can strongly alter bat movements along landscape structures, for light-averse but also light-opportunistic species. Such changes in flight behaviour may involve bypasses or detours, which may force bats to fly longer distances at night which could ultimately affect fitness. Our findings suggest that avoiding artificial lighting close to flight routes will benefit bats.
  • Trends in Ecology and Evolution

    Biological Earth observation with animal sensors

    Walter Jetz, Grigori Tertitski, Roland W. Kays, Uschi Mueller, Martin Wikelski, Susanne Åkesson, Yuriy A. Anisimov, Aleksey Antonov, Walter Arnold, Franz Bairlein, Oriol Baltà, Diane Baum, Mario Beck, Olga Belonovich, Mikhail Belyaev, Matthias Berger, Peter Berthold, Steffen Bittner, Stephen Blake, Barbara Block, Daniel Bloche, Katrin Boehning-Gaese, Gil Bohrer, Julia Bojarinova, Gerhard Bommas, Oleg Bourski, Albert Bragin, Alexandr Bragin, Rachel Bristol, Vojtěch Brlík, Victor N Bulyuk, Francesca Cagnacci, Ben Carlson, Taylor K. Chapple, Kalkidan F. Chefira, Yachang Cheng, Nikita Chernetsov, Grzegorz Cierlik, Simon S. Christiansen, Oriol Clarabuch, William Cochran, Jamie Margaret Cornelius, Iain Couzin, Margret C. Crofoot, Andrea Kölzsch, Morrison Pot, Froukje Rienks, Kamiel Spoelstra, Henk P. van der Jeugd, Marcel E. Visser

    Space-based tracking technology using low-cost miniature tags is now delivering data on fine-scale animal movement at near-global scale. Linked with remotely sensed environmental data, this offers a biological lens on habitat integrity and connectivity for conservation and human health; a global network of animal sentinels of environmental change.

  • Journal of Applied Ecology

    Artificial light at night affects plant‐herbivore interactions

    Ellen Cieraad, Emily Strange, Melanie Flink, Maarten Schrama, Kamiel Spoelstra

    Artificial light at night (ALAN) affects species' physiology and behaviour, and the interactions between species. Despite the importance of plants as primary producers, it remains poorly understood whether and how effects of ALAN on plants cascade through the food web.
    We assess the extent to which ALAN of different spectra result in plant-mediated insect herbivory damage. In a 6-month field experiment, we exposed plants of differing palatability to three colours of ALAN and a dark control, and assessed plant traits (growth rate, leaf size, foliar density and thickness) and insect herbivory (represented by insect damage as loss of foliage to leaf-chewing insects, and gall abundance by phloem-feeding herbivory).
    We found evidence for plant trait-mediated ALAN effects on herbivory for oak, but not for blueberry. In oak, ALAN of different colours changed the direction of relationships of insect damage with relative growth rate and with leaf thickness. Moreover, we found that the effects of ALAN on herbivory damage differed markedly between forest types within the same locale, particularly in the red light treatment.
    Synthesis and applications. Our results provide evidence that continuous night-time light, as provided by street lighting around the world, affects food web interactions. The nature of these effects differed by species and appeared to depend on forest type and the light spectrum employed, thus underlining the context dependency of ALAN in different ecosystems and environmental settings. These findings highlight the complexity of using spectral manipulation as a mitigation measure, and the need for further consideration of ALAN in environmental management and planning, to limit the exposure and impact of cascading effects of artificial light at night on food webs and communities.
  • Frontiers in Ecology and Evolution

    11 Pressing Research Questions on How Light Pollution Affects Biodiversity

    Franz Hölker, Janine Bolliger, Thomas W. Davies, Simone Giavi, Andreas Jechow, Gregor Kalinkat, Travis Longcore, Kamiel Spoelstra, Svenja Tidau, Marcel E. Visser, Eva Knop

    Artificial light at night (ALAN) is closely associated with modern societies and is rapidly increasing worldwide. A dynamically growing body of literature shows that ALAN poses a serious threat to all levels of biodiversity—from genes to ecosystems. Many “unknowns” remain to be addressed however, before we fully understand the impact of ALAN on biodiversity and can design effective mitigation measures. Here, we distilled the findings of a workshop on the effects of ALAN on biodiversity at the first World Biodiversity Forum in Davos attended by several major research groups in the field from across the globe. We argue that 11 pressing research questions have to be answered to find ways to reduce the impact of ALAN on biodiversity. The questions address fundamental knowledge gaps, ranging from basic challenges on how to standardize light measurements, through the multi-level impacts on biodiversity, to opportunities and challenges for more sustainable use.

  • Movement Ecology

    Bats seek refuge in cluttered environment when exposed to white and red lights at night

    Kévin Barré, Christian Kerbiriou, Ros Kiri Ing, Yves Bas, Clémentine Azam, Isabelle Le Viol, Kamiel Spoelstra

    Background: Artificial light at night is recognized as an increasing threat to biodiversity. However, information on the way highly mobile taxa such as bats spatially respond to light is limited. Following the hypothesis of a behavioural adaptation to the perceived risks of predation, we hypothesised that bats should avoid lit areas by shifting their flight route to less exposed conditions. Methods: Using 3D acoustic localization at four experimentally illuminated sites, we studied how the distance to streetlights emitting white and red light affected the Probability of bats Flying Inside the Forest (PFIF) versus along the forest edge. Results: We show that open-, edge-, and narrow-space foraging bats strongly change flight patterns by increasing PFIF when getting closer to white and red streetlights placed in the forest edge. These behavioural changes occurred mainly on the streetlight side where light was directed. Conclusions: The results show that bats cope with light exposure by actively seeking refuge in cluttered environment, potentially due to involved predation risks. This is a clear indication that bats make use of landscape structures when reacting to light, and shows the potential of vegetation and streetlight orientation in mitigating effects of light. The study nevertheless calls for preserving darkness as the most efficient way.

  • Animal Conservation

    Artificial light may change flight patterns of bats near bridges along urban waterways

    Kévin Barré, Kamiel Spoelstra, Yves Bas, S. Challéat, R. Kiri Ing, C. Azam, G. Zissis, D. Lapostolle, Christian Kerbiriou, Isabelle Le Viol
    Abstract Artificial light at night (ALAN) is considered as a major threat to biodiversity, especially to nocturnal species, as it reduces availability, quality and functionality of habitats. However, its effects on the way species use landscape elements such as rivers are still largely understudied, especially the effect of crossing infrastructure lighting on bridges. These elements are nevertheless key commuting and foraging habitats in heavily urbanised landscapes for several taxa such as bats that are particularly affected by ALAN. We studied the effects of the illumination of facades and undersides of bridges on the relative abundance of pipistrelle bats, on their 3D distribution and their behavioural response (i.e. flight speed) close to bridges. We set-up an innovative approach based on a microphone-array to reconstruct positions and flight trajectories in 3D. We studied the effect of lighting on bats in the close proximity of six similar bridges, mostly differentiated by the presence or absence of lighting (3 lit and 3 unlit). All bridges cross the same waterway, within a uniformly and highly urbanized agglomeration (Toulouse, France). We found that bat activity was 1.7 times lower in lit sites. Bats tended to keep a larger distance, and to fly faster close to illuminated bridges. These results suggest that bridge lighting strongly reduces habitat availability and likely connectivity for bats. In that case, results call for switching off the illumination of such bridges crossing riverine ecosystems to preserve their functionality as habitats and corridors for bats.
  • Frontiers in Ecology and Evolution

    Color of Artificial Light at Night Affects Incubation Behavior in the Great Tit, Parus major

    Artificial light at night (ALAN) has been recognized as a biodiversity threat due to the drastic effects it can have on many organisms. In wild birds, artificial illumination alters many natural behaviors that are important for fitness, including chick provisioning. Although incubation is a key determinant of the early developmental environment, studies into the effects of ALAN on bird incubation behavior are lacking. We measured nest temperature in nest boxes of great tits during the incubation period in two consecutive years. Nest boxes were located in eight previously dark field sites that have been experimentally illuminated since 2012 with white, green, or red light, or were left dark. We tested if light treatment affected mean nest temperature, number of times birds leave the nest (off-bout frequency), and off-bout duration during the incubation period. Subsequently, we investigated if incubation behavior is related to fitness. We found that birds incubating in the white light during a cold, early spring had lower mean nest temperatures at the end of incubation, both during the day and during the night, compared to birds in the green light. Moreover, birds incubating in white light took fewer off-bouts, but off-bouts were on average longer. The opposite was true for birds breeding in the green light. Low incubation temperatures and few but long off-bouts can have severe consequences for developing embryos. In our study, eggs from birds that took on average few off-bouts needed more incubation days to hatch compared to eggs from birds that took many off-bouts. Nevertheless, we found no clear fitness effects of light treatment or incubation behavior on the number of hatchlings or hatchling weight. Our results add to the growing body of literature that shows that effects of ALAN can be subtle, can differ due to the spectral composition of light, and can be year-dependent. These subtle alterations of natural behaviors might not have severe fitness consequences in the short-term. However, in the long term they could add up, negatively affecting parent condition and survival as well as offspring recruitment, especially in urban environments where more environmental pollutants are present.
  • BioScience

    The Impact of Light Pollution on Bats Varies According to Foraging Guild and Habitat Context

    Christian C. Voigt, Jasja Dekker, Marcus Fritze, Suren Gazaryan, Franz Hölker, E. B. Gareth Jones, Daniel Lewanzik, Herman J.G.A. Limpens, Fiona Mathews, Jens Rydell, Kamiel Spoelstra, Maja Zagmajster
    We Review How Different Bat Guilds Respond To Artificial Light At Night (Alan) And Assess How The Impacts Can Vary According To Ecological Context. All Studied European Species Respond Negatively To Alan Close To Roosts And Drinking Sites, And The Impacts Occur Across A Wide Range Of Light Colors And Intensities. Most Bat Species Are Sensitive To Alan When Commuting And Foraging. Although Narrow-Space-Foraging Bat Species Consistently Avoid Alan When Foraging, Open And Edge-Space-Foraging Species May Exploit Insects Lured By Alan. Therefore, Alan Acts As An Environmental Filter On Bat Assemblages. Considering The Detrimental Effect Of Alan On Insects, We Conclude That Alan Probably Has Negative Impacts On All Bat Species, Even On Those Foraging At Streetlights. The Sprawl Of Alan May Be A Key Factor Driving The Decline Of Bat Diversity Globally, And The Current Trajectory Of Increasing Alan Is Therefore Of Considerable Concern For Bat Conservation.
  • BioScience


    Christian C. Voigt, Jasja Dekker, Marcus Fritze, Suren Gazaryan, Franz Hölker, E. B. Gareth Jones, Daniel Lewanzik, Herman J.G.A. Limpens, Fiona Mathews, Jens Rydell, Kamiel Spoelstra, Maja Zagmajster

    In the originally published version of this manuscript, there were errors in some of the genus names listed in Table 1. These errors have been corrected.

  • Scientific Reports

    Pollination and fruit infestation under artificial light at night: light colour matters

    Rapid human population growth and associated urbanization lead to increased artificial illumination of the environment. By changing the natural light–dark cycle, artificial lighting can affect the functioning of natural ecosystems. Many plants rely on insects in order to reproduce but these insects are known to be disturbed by artificial light. Therefore, plant–insect interactions may be affected when exposed to artificial illumination. These effects can potentially be reduced by using different light spectra than white light. We studied the effect of artificial lighting on plant–insect interactions in the Silene latifolia–Hadena bicruris system using a field set-up with four different light treatments: red, green, white and a dark control. We compared the proportion of fertilized flowers and fertilized ovules as well as the infestation of fruits by Hadena bicruris, a pollinating seed predator. We found no difference in the proportion of fertilized flowers among the treatments. The proportion of fruits infested by H. bicruris was however significantly higher under green and white light and a significantly lower proportion of fertilized ovules was found under green light. We show that artificial light with different colours impacts plant–insect interactions differently, with direct consequences for plant fitness.
  • Current Biology

    Experimental light at night has a negative long-term impact on macro-moth populations

    Roy H. A. van Grunsven, Jurriën R. van Deijk, Maurice Donners, Frank Berendse, Marcel E. Visser, Elmar M. Veenendaal, Kamiel Spoelstra
    Van Grunsven et al. experimentally test the long-term effects of artificial light on natural moth populations. In the initial two years there was no effect on populations, but in the latter three years population sizes were reduced compared with the dark controls. This shows that artificial light negatively affects moth populations.
  • Ecological Applications

    Artificial light at night, in interaction with spring temperature, modulates timing of reproduction in a passerine bird

    Davide Dominoni, Johan Kjellberg Jensen, Maaike de Jong, Marcel E. Visser, Kamiel Spoelstra
    Abstract The ecological impact of artificial light at night (ALAN) on phenological events such as reproductive timing is increasingly recognized. In birds, previous experiments under controlled conditions showed that ALAN strongly advances gonadal growth, but effects on egg-laying date are less clear. In particular, effects of ALAN on timing of egg-laying are found to be year-dependent, suggesting an interaction with climatic conditions such as spring temperature, which is known have strong effects on the phenology of avian breeding. Thus, we hypothesized that ALAN and temperature interact to regulate timing of reproduction in wild birds. Field studies have suggested that sources of ALAN rich in short wavelengths can lead to stronger advances in egg-laying date. We therefore tested this hypothesis in the great tit (Parus major), using a replicated experimental setup where eight previously unlit forest transects were illuminated with either white, green, or red LED light, or left dark as controls. We measured timing of egg-laying for 619 breeding events spread over six consecutive years and obtained temperature data for all sites and years. We detected overall significantly earlier egg-laying dates in the white and green light versus the dark treatment, and similar trends for red light. However, there was a strong inter-annual variability in mean egg-laying dates in all treatments, which was explained by spring temperature. We did not detect any fitness consequence of the changed timing of egg-laying due to ALAN, which suggests that advancing reproduction in response to ALAN might be adaptive.
  • Methods in Ecology and Evolution

    Comparing diel activity patterns of wildlife across latitudes and seasons: Time transformations using day length

    Carmen Vazquez, J. Marcus Rowcliffe, Kamiel Spoelstra, Patrick A. Jansen
    Abstract Camera trapping allows scientists to study activity patterns of animals under natural conditions. However, comparisons of activity patterns across seasons or latitudes can be biased, because activity is often attuned to sunrise and sunset, the timing of which varies with latitude and season. Existing transformation methods to solve this problem have limitations. Here, we explore whether and how activity patterns can be transformed more accurately using two alternative ?double anchoring? transformations ? equinoctial and average anchoring ? that anchor activity time to two chosen anchor points during the study period. Using simulated noisy datasets mimicking species with either crepuscular, diurnal or cathemeral activity patterns, we compared the ability of different transformation methods to extract the latent pattern and activity levels under different study conditions. We found that average anchoring best retrieved the original diel activity pattern and yielded accurate estimates of activity level. Two alternative transformation methods ? single anchoring and equinoctial anchoring ? performed less well. Bias in estimates from using untransformed clock times was most marked (up to 2.5-fold overestimation) for longer studies covering 4?5 months either side of an equinox at high latitude, and focusing on crepuscular species. We applied the average anchoring method to 9 months of data on Red deer Cervus elaphus, Wild boar Sus scrofa and Mouflon Ovis amon musimon activity as captured by camera traps in National Park Hoge Veluwe, the Netherlands. Average anchoring revealed more pronounced peaks of activity after sunset than was apparent from untransformed data in red deer and wild boar, but not for mouflon, a cathemeral species. Similarly, activity level was lower when calculated using average anchored time for red deer and wild boar, but no difference was observed for mouflon. We conclude that transformation of time might not be necessary at latitudes below 20°, or in studies with a duration of less than a month (below 40° latitude). For longer study periods and/or higher latitudes, average anchoring resolves the problem of variable day length. Code is provided. The transformation functions are incorporated in the r-package ?activity?.
  • Proceedings of the Royal Society B-Biological Sciences

    The preference and costs of sleeping under light at night in forest and urban great tits

    Zeynep Ulgezen, Teemu Käpylä, Peter Meerlo, Kamiel Spoelstra, Marcel E. Visser, Davide Dominoni
    Artificial light at night (ALAN) is an increasing phenomenon associated with worldwide urbanization. In birds, broad-spectrum white ALAN can have disruptive effects on activity patterns, metabolism, stress response and immune function. There has been growing research on whether the use of alternative light spectra can reduce these negative effects, but surprisingly, there has been no study to determine which light spectrum birds prefer. To test such a preference, we gave urban and forest great tits (Parus major) the choice where to roost using pairwise combinations of darkness, white light or green dim light at night (1.5 lux). Birds preferred to sleep under artificial light instead of darkness, and green was preferred over white light. In a subsequent experiment, we investigated the consequence of sleeping under a particular light condition, and measured birds' daily activity levels, daily energy expenditure (DEE), oxalic acid as a biomarker for sleep debt and cognitive abilities. White light affected activity patterns more than green light. Moreover, there was an origin-dependent response to spectral composition: in urban birds, the total daily activity and night activity did not differ between white and green light, while forest birds were more active under white than green light. We also found that individuals who slept under white and green light had higher DEE. However, there were no differences in oxalic acid levels or cognitive abilities between light treatments. Thus, we argue that in naive birds that had never encountered light at night, white light might disrupt circadian rhythms more than green light. However, it is possible that the negative effects of ALAN on sleep and cognition might be observed only under intensities higher than 1.5 lux. These results suggest that reducing the intensity of light pollution as well as tuning the spectrum towards long wavelengths may considerably reduce its impact.
  • Frontiers in Ecology and Evolution

    The Genomics of Circadian Timing in a Wild Bird, the Great Tit (Parus major)

    Veronika Laine, Els Atema, Priscilla Vlaming, Irene C. Verhagen, A.C. Mateman, Jip Ramakers, Kees van Oers, Kamiel Spoelstra, Marcel E. Visser
    Circadian rhythms are ubiquitous among taxa and are essential for coping with recurrent daily events, leading to selection on the properties of the clock underlying these rhythms. To quantify this selection in the wild, we need, however, to phenotype wild individuals, which is difficult using the standard laboratory approach for which individuals need to be kept under constant conditions. To overcome this problem, we explored the possibility to link the variation in a key clock property, circadian period (Tau), to genetic variation. We measured Tau in 152 captive great tits (Parus major). We further linked Tau to two circadian phase markers, the onset of activity in the Light:Dark cycle, and the first onset in constant conditions (Dim:Dim), directly after entrainment. We did a genome-wide association study using a 650k SNP chip, and we linked genetic polymorphisms of a set of twelve candidate genes, to Tau and the two circadian phase markers. In line with earlier studies, Tau was heritable (h2 =0.48 ± 0.22). Despite this genetic variation, we did not find any significant associations at the genome-wide level with the measured traits and only one candidate gene showed association with onset of activity in the Light:Dark cycle. Identifying the genetic base of circadian timing for wild species thus remains challenging. Including alternative molecular methods such as epigenetics or transcriptomics could help to unravel the molecular basis of the biological clock in great tits.
  • Journal of Experimental Zoology Part A: Ecological and Integrative Physiology

    Effects of experimental light at night on extra-pair paternity in a songbird

    Maaike de Jong, K.P. Lamers, Mark Eugster, Jenny Ouyang, Arnaud Da Silva, A.C. Mateman, Roy H. A. van Grunsven, Marcel E. Visser, Kamiel Spoelstra
    Abstract Light pollution is increasing worldwide and significantly affects animal behavior. In birds, these effects include advancement of morning activity and onset of dawn song, which may affect extra-pair paternity. Advanced dawn song of males may stimulate females to engage in extra-pair copulations, and the earlier activity onset may affect the males? mate guarding behavior. Earlier work showed an effect of light at night on extra-pair behavior, but this was in an area with other anthropogenic disturbances. Here, we present a two-year experimental study on effects of light at night on extra-pair paternity of great tits (Parus major). Previously dark natural areas were illuminated with white, red, and green LED lamps and compared to a dark control. In 2014, the proportion of extra-pair young in broods increased with distance to the red and white lamps (i.e., at lower light intensities), but decreased with distance to the poles in the dark control. In 2013, we found no effects on the proportion of extra-pair young. The total number of offspring sired by a male was unaffected by artificial light at night in both years, suggesting that potential changes in female fidelity in pairs breeding close to white and red light did not translate into fitness benefits for the males of these pairs. Artificial light at night might disrupt the natural patterns of extra-pair paternity, possibly negates potential benefits of extra-pair copulations and thus could alter sexual selection processes in wild birds.
  • Proceedings of the Royal Society B-Biological Sciences

    Artificial light at night shifts daily activity patterns but not the internal clock in the great tit (Parus major)

    Kamiel Spoelstra, Irene C. Verhagen, Davy Meijer, Marcel E. Visser
    Artificial light at night has shown a dramatic increase over the last decades and continues to increase. Light at night can have strong effects on the behaviour and physiology of species, which includes changes in the daily timing of activity; a clear example is the advance in dawn song onset in songbirds by low levels of light at night. Although such effects are often referred to as changes in circadian timing, i.e. changes to the internal clock, two alternative mechanisms are possible. First, light at night can change the timing of clock controlled activity, without any change to the clock itself; e.g. by a change in the phase relation between the circadian clock and expression of activity. Second, changes in daily activity can be a direct response to light (‘masking’), without any involvement of the circadian system. Here, we studied whether the advance in onset of activity by dim light at night in great tits (Parus major) is indeed attributable to a phase shift of the internal clock. We entrained birds to a normal light/dark (LD) cycle with bright light during daytime and darkness at night, and to a comparable (LDim) schedule with dim light at night. The dim light at night strongly advanced the onset of activity of the birds. After at least six days in LD or LDim, we kept birds in constant darkness (DD) by leaving off all lights so birds would revert to their endogenous, circadian system controlled timing of activity. We found that the timing of onset in DD was not dependent on whether the birds were kept at LD or LDim before the measurement. Thus, the advance of activity under light at night is caused by a direct effect of light rather than a phase shift of the internal clock. This demonstrates that birds are capable of changing their daily activity to low levels of light at night directly, without the need to alter their internal clock.
  • Ardea

    Timing of avian breeding in an urbanized world

    Maaike de Jong, L. Van den Eertwegh, R. Beskers, Peter De Vries, Kamiel Spoelstra, Marcel E. Visser
    A large part of the world is urbanized, and the process of urbanization is ongoing.
    Species differ in the extent to which they are impacted by urbanization, depending
    on adaption capacity, and on the fitness consequences when adaptation lags
    behind. One prominent effect of urbanization is the dramatic change of the nighttime
    environment: in urban areas nights are no longer dark. Here, we studied the
    impact of urbanization on the timing of breeding, which is a key life-history trait.
    We used six years of data from ten common bird species, breeding in nest boxes
    throughout the Netherlands. We took the intensity of artificial light in the form of
    zenithal sky brightness and light emission, as a proxy for urbanization. We found
    a correlation between light levels and seasonal timing in three of the ten species
    (great tit, blue tit and pied flycatcher), but these relationships differed between
    years. The effect of urbanization on seasonal timing is at best weak in our study
    which was however mainly based on areas with relatively low light levels. There is
    a clear lack of data for breeding birds in more urbanized environments, an ever
    expanding habitat for an increasing number of species worldwide.
  • Journal of Experimental Zoology Part A: Ecological Genetics and Physiology

    No effect of artificial light of different colors on commuting Daubenton's bats (Myotis daubentonii) in a choice experiment

    Progressive illumination at night poses an increasing threat to species worldwide. Light at night is particularly problematic for bats as most species are nocturnal and often cross relatively large distances when commuting between roosts and foraging grounds. Earlier studies have shown that illumination of linear structures in the landscape disturbs commuting bats, and that the response of bats to light may strongly depend on the light spectrum. Here, we studied the impact of white, green, and red light on commuting Daubenton's bats (Myotis daubentonii). We used a unique location where commuting bats cross a road by flying through two identical, parallel culverts underneath. We illuminated the culverts with white, red, and green light,with an intensity of 5 lux at the water surface. Bats had to choose between the two culverts, each with a different lighting condition every night. We presented all paired combinations of white, green, and red light and dark control in a factorial design. Contrary to our expectations, the number of bat passes through a culvert was unaffected by the presence of light. Furthermore, bats did not show any preference for light color. These results show that the response of commuting Daubenton's bats to different colors of light at night with a realistic intensity may be limited when passing through culverts.
  • Philosophical Transactions of the Royal Society B: Biological Sciences

    Methods in field chronobiology

    Davide Dominoni, Susanne Åkesson, Raymond Klaassen, Kamiel Spoelstra, Martin Bulla
    Chronobiological research has seen a continuous development of novel approaches and techniques to measure rhythmicity at different levels of biological organization from locomotor activity (e.g. migratory restlessness) to physiology (e.g. temperature and hormone rhythms, and relatively recently also in genes, proteins and metabolites). However, the methodological advancements in this field have been mostly and sometimes exclusively used only in indoor laboratory settings. In parallel, there has been an unprecedented and rapid improvement in our ability to track animals and their behaviour in the wild. However, while the spatial analysis of tracking data is widespread, its temporal aspect is largely unexplored. Here, we review the tools that are available or have potential to record rhythms in the wild animals with emphasis on currently overlooked approaches and monitoring systems. We then demonstrate, in three question-driven case studies, how the integration of traditional and newer approaches can help answer novel chronobiological questions in free-living animals. Finally, we highlight unresolved issues in field chronobiology that may benefit from technological development in the future. As most of the studies in the field are descriptive, the future challenge lies in applying the diverse technologies to experimental set-ups in the wild.
  • Journal of Biological Rhythms

    Early Birds by Light at Night: Effects of Light Color and Intensity on Daily Activity Patterns in Blue Tits

    Maaike de Jong, Samuel P. Caro, Phillip Gienapp, Kamiel Spoelstra, Marcel E. Visser
    Artificial light at night disturbs the daily rhythms of many organisms. To what extent this disturbance depends on the intensity and spectral composition of light remain obscure. Here, we measured daily activity patterns of captive blue tits (Cyanistes caeruleus) exposed to similar intensities of green, red, or white light at night. Birds advanced their onset of activity in the morning under all light colors but more under red and white light than under green light. Offset of activity was slightly delayed in all light colors. The total activity over a 24-h period did not change but birds moved a part of their daily activity into the night. Since the effect of red and white lights are comparable, we tested the influence of light intensity in a follow-up experiment, where we compared the activity of the birds under different intensities of green and white light only. While in the higher range of intensities, the effects of white and green light were comparable; at lower intensities, green light had a less disturbing effect as compared with white light on daily rhythms in blue tits. Our results show that the extent of this disturbance can be mitigated by modulating the spectral characteristics and intensity of outdoor lighting, which is now feasible through the use of LED lighting.
  • Proceedings of the Royal Society B-Biological Sciences

    Response of bats to light with different spectra: light-shy and agile bat presence is affected by white and green, but not red light

    Kamiel Spoelstra, Roy H. A. van Grunsven, Jip Ramakers, Kim Ferguson, Thomas Raap, Maurice Donners, Elmar M. Veenendaal, Marcel E. Visser
    Artificial light at night has shown a remarkable increase over the past decades. Effects are reported for many species groups, and include changes in presence, behaviour, physiology and life-history traits. Among these, bats are strongly affected, and how bat species react to light is likely to vary with light colour. Different spectra may therefore be applied to reduce negative impacts. We used a unique set-up of eight field sites to study the response of bats to three different experimental light spectra in an otherwise dark and undisturbed natural habitat. We measured activity of three bat species groups around transects with light posts emitting white, green and red light with an intensity commonly used to illuminate countryside roads. The results reveal a strong and spectrum-dependent response for the slow-flying Myotis and Plecotus and more agile Pipistrellus species, but not for Nyctalus and Eptesicus species. Plecotus and Myotis species avoided white and green light, but were equally abundant in red light and darkness. The agile, opportunistically feeding Pipistrellus species were significantly more abundant around white and green light, most likely because of accumulation of insects, but equally abundant in red illuminated transects compared to dark control. Forest-dwelling Myotis and Plecotus species and more synanthropic Pipistrellus species are thus least disturbed by red light. Hence, in order to limit the negative impact of light at night on bats, white and green light should be avoided in or close to natural habitat, but red lights may be used if illumination is needed.
  • Frontiers in Ecology and Evolution

    Artificial Light at Night Reduces Daily Energy Expenditure in Breeding Great Tits (Parus major)

    Anouk Welbers, Natalie van Dis, Annemieke Kolvoort, Jenny Ouyang, Marcel E. Visser, Kamiel Spoelstra, Davide Dominoni
    The ecological impact of artificial light at night (ALAN) is an increasingly recognized process that accompanies expanding urbanization. Yet, we have limited knowledge on the impact of ALAN on wild species, and on the potential to mitigate any negative effects by using different light sources and colors. In birds, effects of ALAN on activity levels are reported for several species and, hence, their daily energy expenditure (DEE) may be affected. DEE is a potent mediator of life-history trade-offs and fitness and thus an important aspect to consider when examining the potential long-term ecological effects of ALAN. Previous work has suggested that birds exposed to ALAN show higher levels of provisioning and nocturnal activity, suggesting that white ALAN increases DEE. Other factors regulating DEE, such as provisioning behavior and food availability, might also respond to ALAN and thus indirectly affect DEE. We tested the hypothesis that ALAN increases DEE using an experimental setup where four previously unlit transects were illuminated with either white, green, or red LED light, or left dark as a control treatment. This setup was replicated in eight locations across the Netherlands. We measured DEE of our focal species, the great tit (Parus major), using a novel doubly labeled water technique that uses breath rather than blood samples. Contrary to our expectations, birds feeding their offspring under white and green ALAN showed lower DEE compared to birds in the control dark treatment. Differences in chick provisioning activity did not explain this result, as neither visit rates nor daily activity timing was affected by light treatment. However, food availability under white and green light was much higher compared to red light and the dark control. This difference strongly suggests that the lower DEE under white and green ALAN sites is a consequence of higher food availability in these treatments. This result shows that there can be positive, indirect effects of ALAN for breeding song birds which may balance against the negative direct effects shown in previous studies.
  • Royal Society Open Science

    Experimental illumination of a forest: no effects of lights of different colours on the onset of the dawn chorus in songbirds

    Arnaud Da Silva, Maaike de Jong, Roy H. A. van Grunsven, Marcel E. Visser, Bart Kempenaers, Kamiel Spoelstra
    Light pollution is increasing exponentially, but its impact on animal behaviour is still poorly understood. For songbirds, the most repeatable finding is that artificial night lighting leads to an earlier daily onset of dawn singing. Most of these studies are, however, correlational and cannot entirely dissociate effects of light pollution from other effects of urbanization. In addition, there are no studies in which the effects of different light colours on singing have been tested. Here, we investigated whether the timing of dawn singing in wild songbirds is influenced by artificial light using an experimental set-up with conventional street lights. We illuminated eight previously dark forest edges with white, green, red or no light, and recorded daily onset of dawn singing during the breeding season. Based on earlier work, we predicted that onset of singing would be earlier in the lighted treatments, with the strongest effects in the early-singing species. However, we found no significant effect of the experimental night lighting (of any colour) in the 14 species for which we obtained sufficient data. Confounding effects of urbanization in previous studies may explain these results, but we also suggest that the experimental night lighting may not have been strong enough to have an effect on singing.
  • Global Change Biology

    What type of rigorous experiments are needed to investigate the impact of artificial light at night on individuals and populations?

    Jenny Ouyang, Maaike de Jong, Roy H. A. van Grunsven, Kevin D. Matson, Mark F. Haussmann, Peter Meerlo, Marcel E. Visser, Kamiel Spoelstra
  • Global Change Biology

    Restless roosts: Light pollution affects behavior, sleep, and physiology in a free-living songbird

    Jenny Ouyang, Maaike de Jong, Roy H. A. van Grunsven, Kevin D. Matson, Mark F. Haussmann, Peter Meerlo, Marcel E. Visser, Kamiel Spoelstra
    The natural nighttime environment is increasingly polluted by artificial light. Several studies have linked artificial light at night to negative impacts on human health. In free-living animals, light pollution is associated with changes in circadian, reproductive, and social behavior, but whether these animals also suffer from physiologic costs remains unknown. To fill this gap, we made use of a unique network of field sites which are either completely unlit (control), or are artificially illuminated with white, green, or red light. We monitored nighttime activity of adult great tits, Parus major, and related this activity to within-individual changes in physiologic indices. Because altered nighttime activity as a result of light pollution may affect health and well-being, we measured oxalic acid concentrations as a biomarker for sleep restriction, acute phase protein concentrations and malaria infection as indices of immune function, and telomere lengths as an overall measure of metabolic costs. Compared to other treatments, individuals roosting in the white light were much more active at night. In these individuals, oxalic acid decreased over the course of the study. We also found that individuals roosting in the white light treatment had a higher probability of malaria infection. Our results indicate that white light at night increases nighttime activity levels and sleep debt and affects disease dynamics in a free-living songbird. Our study offers the first evidence of detrimental effects of light pollution on the health of free-ranging wild animals.
  • PLoS One

    Do wild great tits avoid exposure to light at night?

    Maaike de Jong, Jenny Ouyang, Roy H. A. van Grunsven, Marcel E. Visser, Kamiel Spoelstra
    Studies of wild populations have provided important insights into the effects of artificial light at night on organisms, populations and ecosystems. However, in most studies the exact amount of light at night individuals are exposed to remains unknown. Individuals can potentially control their nighttime light exposure by seeking dark spots within illuminated areas. This uncertainty makes it difficult to attribute effects to a direct effect of light at night, or to indirect effects, e.g., via an effect of light at night on food availability. In this study, we aim to quantify the nocturnal light exposure of wild birds in a previously dark forest-edge habitat, experimentally illuminated with three different colors of street lighting, in comparison to a dark control. During two consecutive breeding seasons, we deployed male great tits (Parus major) with a light logger measuring light intensity every five minutes over a 24h period. We found that three males from pairs breeding in brightly illuminated nest boxes close to green and red lamp posts, were not exposed to more artificial light at night than males from pairs breeding further away. This suggests, based on our limited sample size, that these males could have been avoiding light at night by choosing a roosting place with a reduced light intensity. Therefore, effects of light at night previously reported for this species in our experimental set-up might be indirect. In contrast to urban areas where light is omnipresent, bird species in non-urban areas may evade exposure to nocturnal artificial light, thereby avoiding direct consequences of light at night.
  • Physiology & Behavior

    Dose-dependent responses of avian daily rhythms to artificial light at night

    Maaike de Jong, Lizanne Jeninga, Jenny Ouyang, Kees van Oers, Kamiel Spoelstra, Marcel E. Visser
    Recent studies have shown that animals are affected by night-time light exposure. Light is a continuous variable, but our knowledge on how individuals react to different light intensities during the night is limited. We therefore determined the relationship between night light intensity and the behaviour and physiology of great tits (Parus major). We measured daily activity patterns and melatonin levels in 35 males exposed to five different light intensities and found strong, dose-dependent effects. Activity onset was increasingly advanced, and activity offset delayed with higher light intensities. Furthermore, night-time activity increased and melatonin levels measured at midnight decreased with higher intensities. In this experimental study, we demonstrate for the first time dose-dependent effects of artificial light at night on birds' daily activity patterns and melatonin levels. Our results imply that these effects are not limited to a certain threshold, but emerge even when nocturnal light levels are slightly increased. However, in a natural area, these effects may be limited as artificial light levels are commonly low; light intensities drop rapidly with distance from a light source and birds can avoid exposure to light at night. Future studies should thus focus on examining the impact of different intensities of light at night in the wild.
  • Proceedings of the National Academy of Sciences of the United States of America

    Natural selection against a circadian clock gene mutation in mice

    Kamiel Spoelstra, Martin Wikelski, Serge Daan, Andrew Loudon, Michaela Hau
    Circadian rhythms with an endogenous period close or equal to the natural light-dark cycle are considered evolutionarily adaptive (‘circadian resonance hypothesis’). Despite remarkable insight into the molecular mechanisms driving circadian cycles, this hypothesis has not been tested under natural conditions for any eukaryotic organism. We tested this in mice bearing a short-period mutation in the enzyme casein kinase 1 (tau mutation) which accelerates free-running circadian cycles. We compared daily activity (feeding) rhythms, survivorship and reproduction in six replicate populations in outdoor experimental enclosures, established with wild-type, hetero- or homozygous mice in a Mendelian ratio. In the release cohort, survival was reduced in the homozygote mutant mice revealing strong selection against short-period genotypes. Over the course of 14 months, the relative frequency of the tau allele dropped from initial parity to 20%. Adult survival and recruitment of juveniles into the population contributed about equally to the selection for wild type alleles. The expression of activity during daytime varied throughout the experiment and was significantly increased by the tau mutation. The strong selection against the short-period tau allele observed here contrasts with earlier studies showing absence of selection against a Per2 mutation, which disrupts internal clock function, but does not change period length. These findings are consistent with, and predicted by the theory that resonance of the circadian system plays an important role in individual fitness.
  • Trends in Ecology & Evolution

    A framework to assess evolutionary responses to anthropogenic light and sound

    John P. Swaddle, Clinton D. Francis, Jesse R. Barber, Caren B. Cooper, Christopher C.M. Kyba, Davide Dominoni, Graeme Shannon, Erik Aschehoug, Sarah E. Goodwin, Akito Y. Kawahara, David Luther, Kamiel Spoelstra, Margaret Voss, Travis Longcore
    Human activities have caused a near-ubiquitous and evolutionarily-unprecedented increase in environmental sound levels and artificial night lighting. These stimuli reorganize communities by interfering with species-specific perception of time-cues, habitat features, and auditory and visual signals. Rapid evolutionary changes could occur in response to light and noise, given their magnitude, geographical extent, and degree to which they represent unprecedented environmental conditions. We present a framework for investigating anthropogenic light and noise as agents of selection, and as drivers of other evolutionary processes, to influence a range of behavioral and physiological traits such as phenological characters and sensory and signaling systems. In this context, opportunities abound for understanding contemporary and rapid evolution in response to human-caused environmental change.
  • Philosophical Transactions of the Royal Society B

    Effects of nocturnal illumination on life-history decisions and fitness in two wild songbird species

    Maaike de Jong, Jenny Ouyang, Arnaud Da Silva, Roy H. A. van Grunsven, Bart Kempenaers, Marcel E. Visser, Kamiel Spoelstra
    The effects of artificial night lighting on animal behaviour and fitness are largely unknown. Most studies report short-term consequences in locations that are also exposed to other anthropogenic disturbance. We know little about how the effects of nocturnal illumination vary with different light colour compositions. This is increasingly relevant as the use of LED lights becomes more common, and LED light colour composition can be easily adjusted. We experimentally illuminated previously dark natural habitat with white, green and red light, and measured the effects on life-history decisions and fitness in two free-living songbird species, the great tit (Parus major) and pied flycatcher (Ficedula hypoleuca) in two consecutive years. In 2013, but not in 2014, we found an effect of light treatment on lay date, and of the interaction of treatment and distance to the nearest lamp post on chick mass in great tits but not in pied flycatchers. We did not find an effect in either species of light treatment on breeding densities, clutch size, probability of brood failure, number of fledglings and adult survival. The finding that light colour may have differential effects opens up the possibility to mitigate negative ecological effects of nocturnal illumination by using different light spectra. artificial light at nightlight spectralife-historyfitnessParus majorFicedula hypoleucaFootnotesOne contribution of 14 to a theme issue ‘The biological impacts of artificial light at night: from molecules to communities’.© 2015 The Author(s) Published by the Royal Society. All rights reserved.
  • Philosophical Transactions of the Royal Society B: Biological Sciences

    Experimental illumination of natural habitat—an experimental set-up to assess the direct and indirect ecological consequences of artificial light of different spectral composition

    Kamiel Spoelstra, Roy H. A. van Grunsven, Maurice Donners, Phillip Gienapp, Martinus E. Huigens, Roy Slaterus, Frank Berendse, Marcel E. Visser, Elmar M. Veenendaal
    Artificial night-time illumination of natural habitats has increased dramatically over the past few decades. Generally, studies that assess the impact of artificial light on various species in the wild make use of existing illumination and are therefore correlative. Moreover, studies mostly focus on short-term consequences at the individual level, rather than long-term consequences at the population and community level—thereby ignoring possible unknown cascading effects in ecosystems. The recent change to LED lighting has opened up the exciting possibility to use light with a custom spectral composition, thereby potentially reducing the negative impact of artificial light. We describe here a large-scale, ecosystem-wide study where we experimentally illuminate forest-edge habitat with different spectral composition, replicated eight times. Monitoring of species is being performed according to rigid protocols, in part using a citizen-science-based approach, and automated where possible. Simultaneously, we specifically look at alterations in behaviour, such as changes in activity, and daily and seasonal timing. In our set-up, we have so far observed that experimental lights facilitate foraging activity of pipistrelle bats, suppress activity of wood mice and have effects on birds at the community level, which vary with spectral composition. Thus far, we have not observed effects on moth populations, but these and many other effects may surface only after a longer period of time. experimental lightingpopulation dynamicsdaily timingseasonal timingcascading effectscitizen scienceFootnotesOne contribution of 14 to a theme issue ‘The biological impacts of artificial light at night: from molecules to communities’.© 2015 The Author(s) Published by the Royal Society. All rights reserved.
  • Biology Letters

    Stressful colours: corticosterone concentrations in a free-living songbird vary with the spectral composition of experimental illumination

    Jenny Ouyang, Maaike de Jong, Michaela Hau, Marcel E. Visser, Roy H. A. van Grunsven, Kamiel Spoelstra
    Organisms have evolved under natural daily light/dark cycles for millions of years. These cycles have been disturbed as night-time darkness is increasingly replaced by artificial illumination. Investigating the physiological consequences of free-living organisms in artificially lit environments is crucial to determine whether nocturnal lighting disrupts circadian rhythms, changes behaviour, reduces fitness and ultimately affects population numbers. We make use of a unique, large-scale network of replicated field sites which were experimentally illuminated at night using lampposts emanating either red, green, white or no light to test effect on stress hormone concentrations (corticosterone) in a songbird, the great tit (Parus major). Adults nesting in white-light transects had higher corticosterone concentrations than in the other treatments. We also found a significant interaction between distance to the closest lamppost and treatment type: individuals in red light had higher corticosterone levels when they nested closer to the lamppost than individuals nesting farther away, a decline not observed in the green or dark treatment. Individuals with high corticosterone levels had fewer fledglings, irrespective of treatment. These results show that artificial light can induce changes in individual hormonal phenotype. As these effects vary considerably with light spectrum, it opens the possibility to mitigate these effects by selecting street lighting of specific spectra.
  • Annual Review of Chronopharmacology

    Compression of daily activity time in mice lacking functional Per or Cry genes

    Kamiel Spoelstra, M. Comas, Serge Daan
    The adjustment of daily activity time (alpha) to the varying night length in nocturnal creatures was one of the functions originally attributed to a putative dual oscillator structure of circadian pacemakers in mammals. In two experimental approaches, we tested whether this ability is compromised in mice with functional deletions of one of the four circadian clock genes. First, we tested the capability of alpha compression by long days in mPer1(Brdm1) and mPer2(Brdm1) mutant mice. When exposed to a full L:D 18:6 photoperiod, wild-type and mPer1(Brdm1) mutant mice show compression followed by decompression of alpha in DD. mPer2(Brdm1) mutant mice did not compress their activity time. The interpretation of these data is, however, complicated by masking due to light. We, therefore, embarked on a second experiment, exploiting skeleton photoperiods. The skeleton photoperiod was changed stepwise from 0 to 24 h, and mCry1 and mCry2 knockout mice were now included in the design. We observed clear and systematic compression of alpha in wild-type and mCry1 and mCry2 knockout mice. mPer1(Brdm1) and mPer2(Brdm1) mice both poorly entrained to the skeleton photoperiod. The single mPer2(Brdm1) mutant mouse that did entrain did not show alpha compression. The results show that neither mCry1 nor mCry2 deletions compromise adjustment to day length, consistent with our earlier conclusions on period lengthening in constant light (Spoelstra & Daan, 2008). The mPer2(Brdm1) mutant behaves aberrantly and appears not to respond to the delaying action of light in the late subjective day. [KEYWORDS: Alpha compression circadian clock Cry1 Cry2 Per1 Per2 Mus musculus photoperiod MAMMALIAN CIRCADIAN CLOCK SUPRACHIASMATIC NUCLEUS NOCTURNAL RODENTS CONSTANT LIGHT MUTANT MICE IN-VITRO DROSOPHILA EXPRESSION PACEMAKERS MPER2 Biology Physiology]
  • Proceedings of the Royal Society B-Biological Sciences

    When the sun never sets: Diverse activity rhythms under continuous daylight in free-living arctic-breeding birds

    Silke Steiger, Mihai Valcu, Kamiel Spoelstra, B. Helm, Martin Wikelski, Bart Kempenaers
    Circadian clocks are centrally involved in the regulation of daily behavioural and physiological processes. These clocks are synchronized to the 24 h day by external cues (Zeitgeber), the most important of which is the light–dark cycle. In polar environments, however, the strength of the Zeitgeber is greatly reduced around the summer and winter solstices (continuous daylight or continuous darkness). How animals time their behaviour under such conditions has rarely been studied in the wild. Using a radio-telemetry-based system, we investigated daily activity rhythms under continuous daylight in Barrow,
    Alaska, throughout the breeding season in four bird species that differ in mating system and parental behaviour. We found substantial diversity in daily activity rhythms depending on species, sex and breeding stage. Individuals exhibited either robust, entrained 24 h activity cycles, were continuously active (arrhythmic) or showed ‘free-running’ activity cycles. In semipalmated
    sandpipers, a shorebird with biparental incubation, we show that the free-running rhythm is synchronized between pair mates. The diversity of diel timekeeping under continuous daylight emphasizes the plasticity of the circadian system, and the importance of the social and life-history context. Our results support the idea that circadian behaviour can be adaptively modified to
    enable species-specific time-keeping under polar conditions
  • Annual Review of Chronopharmacology

    Effects of temperature on circadian clock and chronotype: an experimental study in a passerine bird

    M. Lehmann, Kamiel Spoelstra, Marcel E. Visser, B. Helm
    Daily schedules of many organisms, including birds, are thought to affect fitness. Timing in birds is based on circadian clocks that have a heritable period length, but fitness consequences for individuals in natural environments depend on the scheduling of entrained clocks. This chronotype, i.e., timing of an individual relative to a zeitgeber, results from interactions between the endogenous circadian clock and environmental factors, including light conditions and ambient temperature. To understand contributions of these factors to timing, we studied daily activity patterns of a captive songbird, the great tit (Parus major), under different temperature and light conditions. Birds were kept in a light (L)-dark (D) cycle (12.5 L:11.5 D) at either 8°C or 18°C with ad libitum access to food and water. We assessed chronotype and subsequently tested birds at the same temperature under constant dim light (LLdim) to determine period length of their circadian clock. Thermal conditions were then reversed so that period length was measured under both temperatures. We found that under constant dim light conditions individuals lengthened their free-running period at higher temperatures by 5.7 ± 2.1 min (p = .002). Under LD, birds kept at 18°C started activity later and terminated it much earlier in the day than those kept under 8°C. Overall, chronotype was slightly earlier under higher temperature, and duration of activity was shorter. Furthermore, individuals timed their activities consistently on different days under LD and over the two test series under LLdim (repeatability from .38 to .60). Surprisingly, period length and chronotype did not show the correlation that had been previously found in other avian species. Our study shows that body clocks of birds are precise and repeatable, but are, nonetheless, affected by ambient temperature.
  • PLoS One

    Activity patterns during food provisioning are affected by artificial light in free living great tits (Parus major)

    Mieke Titulaer, Kamiel Spoelstra, Cynthia Lange, Marcel E. Visser
    Artificial light may have severe ecological consequences but there is limited experimental work to assess these consequences. We carried out an experimental study on a wild population of great tits (Parus major) to assess the impact of light pollution on daily activity patterns during the chick provisioning period. Pairs that were provided with a small light outside their nest box did not alter the onset, cessation or duration of their working day. There was however a clear effect of artificial light on the feeding rate in the second half of the nestling period: when provided with artificial light females increased their feeding rate when the nestlings were between 9 and 16 days old. Artificial light is hypothesised to have affected the perceived photoperiod of either the parents or the offspring which in turn led to increased parental care. This may have negative fitness consequences for the parents, and light pollution may thus create an ecological trap for breeding birds.
  • Journal of Biological Rhythms

    Lab mice in the field: unorthodox daily activity and effects of a dysfunctional circadian clock allele

    Serge Daan, Kamiel Spoelstra, U. Albrecht, I. Schmutz, M. Daan, B. Daan, Froukje Rienks, I. Poletaeva, G. Dell'Omo, A. Vyssotski, H.P. Lipp
    Daily patterns of animal behavior are potentially of vast functional importance. Fitness benefits have been identified in nature by the association between individual timing and survival or by the fate of individuals after experimental deletion of their circadian pacemaker. The recent advances in unraveling the molecular basis of circadian timing enable new approaches to natural selection on timing. The investigators report on the effect and fate of the mutant Per2Brdm1 allele in 4 replicate populations of house mice in a seminatural outside environment over 2 years. This allele is known to compromise circadian organization and entrainment and to cause multiple physiological disturbances. Mice (N = 250) bred from Per2Brdm1 heterozygotes were implanted subcutaneously with transponders and released in approximately Mendelian ratios in four 400 m2 pens. An electronic system stored the times of all visits to feeders of each individual. The study first demonstrates that mice are not explicitly nocturnal in this natural environment. Feeding activity was predominantly and sometimes exclusively diurnal and spread nearly equally over day and night under the protective snow cover in winter. The effect of Per2Brdm1 on activity timing is negligible compared to seasonal changes in all genotypes. Second, the Per2Brdm1 allele did not have persistent negative effects on fitness. In the first year, the allele gradually became less frequent by reducing survival. New cohorts captured had the same Per2Brdm1 frequency as the survivors from previous cohorts, consistent with an absence of an effect on reproduction. In the second year, the allele recovered to about its initial frequency (0.54). These changes in selective advantage were primarily due to female mice, as females lived longer and the sex ratio dropped to about 25% males in the population. While it is unknown which selective advantage led to the recovery, the results caution against inferences from laboratory experiments on fitness consequences in the natural environment. It also demonstrates that the activity of mice, while strictly nocturnal in the laboratory, may be partially or completely diurnal in the field. The new method allows assessment of natural selection on specific alleles on a day-today basis.
  • Functional Ecology

    Radiotelemetry reveals variation in fever and sickness behaviours with latitude in a free-living passerine

    James S. Adelman, Sergio Córdoba-Córdoba, Kamiel Spoelstra, Martin Wikelski, Michaela Hau

    1. The acute phase immune response, which includes fever and sickness behaviours, carries high costs in energy and time, but enhances pathogen clearance in diverse hosts. Hypotheses based upon pathogen pressures and life-historytrade-offs predict that costly immune responses will decrease in strength as latitude increases. However, whether the acute phase response shows latitudinal patterns among free-living, wild populations remains unknown. 2. Here, we studied feverand sickness behaviours during the early breeding season in free-living song sparrows (Melospiza melodia) along a latitudinal gradient in southern California (CA), Washington (WA), and Alaska (AK). In 2007 and 2008, we injected males with lipopolysaccha-ride and assessed sickness behaviour by measuring changes in territorial aggression. In 2008, we monitoredfever and sickness behaviour in CA and WA birds using a novel telemetric technique: skin-mounted radiotransmitters with temperature sensors. 3. In 2007, territorial defence varied by latitude, with a lower probability of territorial response at24 h after injection in CA, but not in WA or AK. Radiotelemetry in 2008 revealed that CA birds showed pronounced and prolonged lethargy and fever (c. 2 °C above control males throughout the night), whereas WA birds showed only moderate lethargy and fever (c. 1 °C, returning to control levels during the night). 4. This study establishes radiotelemetry asa powerful method for quantifying fever and sickness behaviours in small, free-living vertebrates. Moreover, our data suggest that latitude predicts the strength of these responses. These results can provide insight into disease susceptibility and spread among wild populations.

  • Biology Letters

    Sleeping outside the box

    Niels C. Rattenborg, Bryson Voirin, Alexei L. Vyssotski, Roland W. Kays, Kamiel Spoelstra, Franz Kuemmeth, Wolfgang Heidrich, Martin Wikelski

    The functions of sleep remain an unresolved question in biology. One approach to revealing sleep's purpose is to identify traits that explain why some species sleep more than others. Recent comparative studies of sleep have identified relationships between various physiological, neuroanatomical and ecological traits, and the time mammals spend in rapid eye movement (REM) and non-REM sleep. However, owing to technological constraints, these studies were based exclusively on animals in captivity. Consequently, it is unclear to what extent the unnatural laboratory environment affected time spent sleeping, and thereby the identification and interpretation of informative clues to the functions of sleep. We performed the first electroencephalogram (EEG) recordings of sleep on unrestricted animals in the wild using a recently developed miniaturized EEG recorder, and found that brown-throated three-toed sloths (Bradypus variegatus) inhabiting the canopy of a tropical rainforest only sleep 9.63 h d-1, over 6h less than previously reported in captivity. Although the influence of factors such as the age of the animals studied cannot be ruled out, our results suggest that sleep in the wild may be markedly different from that in captivity. Additional studies of various species are thus needed to determine whether the relationships between sleep duration and various traits identified in captivity are fundamentally different in the wild. Our initial study of sloths demonstrates the feasibility of this endeavour, and thereby opens the door to comparative studies of sleep occurring within the ecological context within which it evolved.

  • Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology

    Effects of constant light on circadian rhythmicity in mice lacking functional cry genes

    Kamiel Spoelstra, Serge Daan

    Mutations in each of the genes mPer1, mPer2, mCry1 and mCry2 separately cause deviations from the wild type circadian system. Differences between these mutant strains have inspired the hypothesis that the duality of circadian genes (two mPer and two mCry genes involved) is related to the existence of two components in the circadian oscillator (Daan et al., J Biol Rhythms 16:105-116, 2001). We tested the predictions from this theory that the circadian period (τ) lengthens under constant illumination (LL) in mCry1 and mPer1 mutant mice, while it shortens in mCry2 and mPer2 mutants. mCry1 -/- and mCry2 -/- knockout mice both consistently increased τ with increasing light intensity, as did wild type mice. With increasing illumination, rhythmicity is reduced in mCry1, mCry2 and mPer1, but not in mPer2 deficient mice. Results for mPer mutant mice are in agreement with data reported on these strains earlier by Steinlechner et al. (J Biol Rhythms 17:202-209, 2002), and also with the predictions from the model. The increase in cycle length of the circadian system by light in the mCry2 deficient mice violates the predictions. The model is thereby rejected: the mCry genes do not play a differential role, although the opposite responses of mPer mutants to light remain consistent with a functional Evening-Morning differentiation.

  • Journal of Biological Rhythms

    Circadian response reduction in light and response restoration in darkness

    M. Comas, Domien G. M. Beersma, Kamiel Spoelstra, Serge Daan

    Entrainment may involve responses to dawn, to dusk, and to the light in between these transitions. Previous studies showed that the circadian system responds to only 2 light pulses, one at the beginning and one at the end of the day, in a similar way as to a full photoperiod, as long as the photoperiod is less than approximately 1/2 τ. The authors used a double 1-h light pulse protocol with different intervals of darkness in between (1, 2, 4, 7, 10, and 16 h) to study the phase responses of mice. The phase response curves obtained were compared to full light pulse PRCs of corresponding durations. Up to 6 hours, phase responses induced by double light pulses are virtually the same as by a corresponding full light pulse. The authors made a simple phase-only model to estimate the response reduction due to light exposure and response restoration due to dark exposure of the system. In this model, they assumed a 100% contribution of the first 1-h light pulse and fitted the reduction factor for the second light pulse to yield the best fit to the observations. The results suggest that after 1 h of light followed by less than 4 h of darkness, there is a considerable reduction in response to the second light pulse. Full response restoration requires more than 10 h of darkness. To investigate the influence of the duration of light on the response saturation, the authors performed a second series of experiments where the duration of the 2 light pulses was varied from 4 to 60 min each with a fixed duration of the stimulus (4 h). The response to 2 light pulses saturates when they are between 30 and 60 min long. In conclusion, double pulses replace single full light pulses of a corresponding duration of up to 6 h due to a response reduction during light, combined with response restoration during darkness. By the combined response reduction and response restoration, mice can maintain stable entrainment to the external LD cycle without being continuously exposed to it.

  • Journal of Biological Rhythms

    Phase and period responses of the circadian system of mice (Mus musculus) to light stimuli of different duration

    M. Comas, Domien G. M. Beersma, Kamiel Spoelstra, Serge Daan

    To understand entrainment of circadian systems to different photoperiods in nature, it is important to know the effects of single light pulses of different durations on the free-running system. The authors studied the phase and period responses of laboratory mice (C57BL6J//OlaHsd) to single light pulses of 7 different durations (1, 3, 4, 6, 9, 12, and 18 h) given once per 11 days in otherwise constant darkness. Light-pulse duration affected both amplitude and shape of the phase response curve. Nine-hour light pulses yielded the maximal amplitude PRC. As in other systems, the circadian period slightly lengthened following delays and shortened following advances. The authors aimed to understand how different parts of the light signal contribute to the eventual phase shift. When PRCs were plotted using the onset, midpoint, and end of the pulse as a phase reference, they corresponded best with each other when using the mid-pulse. Using a simple phase-only model, the authors explored the possibility that light affects oscillator velocity strongly in the 1st hour and at reduced strength in later hours of the pulse due to photoreceptor adaptation. They fitted models based on the 1-h PRC to the data for all light pulses. The best overall correspondence between PRCs was obtained when the effect of light during all hours after the first was reduced by a factor of 0.22 relative to the 1st hour. For the predicted PRCs, the light action centered on average at 38% of the light pulse. This is close to the reference phase yielding best correspondence at 36% of the pulses. The result is thus compatible with an initial major contribution of the onset of the light pulse followed by a reduced effect of light responsible for the differences between PRCs for different duration pulses. The authors suggest that the mid-pulse is a better phase reference than lights-on to plot and compare PRCs of different light-pulse durations.

  • Journal of Biological Rhythms

    Phase responses to light pulses in mice lacking functional per or cry genes

    Kamiel Spoelstra, Urs Albrecht, Gijsbertus T.J. Van Der Horst, Verena Brauer, Serge Daan

    The phase-resetting properties of the circadian system in mice with a functional deletion in mCry1, mCry2, mPer1, or mPer2 were studied in 2 experiments. In experiment 1, mCry1-/- and mCry2-/- mice as well as mPer1Brdm1 and mPer2Brdm1 mutant mice were exposed to 15-min light pulses during the 1st cycle following entrainment, either early (external time [ExT] 20) or late (ExT 4) in the subjective night. In experiment 2, a full PRC was measured for all these strains by exposure to light pulses of the same duration and intensity in free-running conditions in constant darkness. Directly after entrainment (experiment 1), mPer1 Brdm1 animals did not show significant phase advances by a light pulse in the late subjective night (ExT 4), as in the study by Albrecht et al. In the same experiment, mPer2Brdm1 mice became arrhythmic too frequently to reliably measure their phase responses. Mice with a targeted gene disruption in mCry1 or mCry2 showed increased phase delays compared to wild type after exposure to a light pulse in the early subjective night (ExT 20). Otherwise, phase shifts were not significantly affected. In free run (experiment 2), all genotypes did show phase advances and phase delays. The mPer2 Brdm1 mutant PRC was above the mPer1Brdm1 mutant and wild-type PRC (i.e., less delayed and more advanced) at most circadian phases. The mPer1Brdm1 mutant PRC was not distinguishable from the wild-type PRC. The mCry2-/- mice showed much smaller phase delays than did mCry1-/- mice in the subjective evening (delay phase). In general, mPer2Brdm1 mutant mice were more accelerated by light compared to mPer1Brdm1 and wild-type control mice, whereas mCry1-/- mice were more delayed by light than were mCry2-/- mice.

  • Journal of Biological Rhythms

    Restoration of self-sustained circadian rhythmicity by the mutant Clock allele in mice in constant illumination

    Kamiel Spoelstra, M. Oklejewicz, Serge Daan

    Mice mutant for the Clock gene display abnormal circadian behavior characterized by long circadian periods and a tendency to become rapidly arrhythmic in constant darkness (DD). To investigate whether this result is contingent on the absence of light, the authors studied the circadian behavior of homozygous Clock mutant mice under conditions of both constant light and DD. Fourteen of 15 Clock/Clock mice stayed rhythmic in constant light of 70 to 170 lux, where 10 of 15 wild-type mice became arrhythmic. In contrast, only 5 of 15 Clock/Clock mice and 15 of 15 wild-type mice remained rhythmic after 60 cycles when released in DD (dim red light of < 1.5 lux) after 8 days of entrainment. The restoration of self-sustained rhythmicity by the Clock allele cannot be attributed to reduced sensitivity of the system to light. It underscores the fact that self-sustainment is not a secure guide to functional organization.

  • Zeitschrift fur Saugetierkunde

    Ground squirrel activity during the solar eclipse of August 11, 1999

    Kamiel Spoelstra, A. M. Strijkstra, Serge Daan
  • Journal of Biological Rhythms

    Accuracy of Human Circadian Entrainment under Natural Light Conditions

    Domien G. M. Beersma, Kamiel Spoelstra, Serge Daan

    The patterns of light intensity to which humans expose their circadian pacemakers in daily life are very irregular and vary greatly from day to day. The circadian pacemaker can adjust to such irregular exposure patterns by daily phase shifts, such as summarized in a phase response curve. It is demonstrated in this paper on the basis of computer simulations applying actually recorded human light exposure patterns that the pacemaker can substantially improve its accuracy by an additional response to light: For that purpose, it should additionally change its angular velocity (and consequently its period [.tau]) in response to light. Reductions of [.tau] in response to light in the morning and increases of [.tau] in response to light in the evening can lead to an increase in entrained pacemaker accuracy with about 25%. Circadian pacemakers have evolved as accurate internal representations of external time, and investigated diurnal mammals all seem to respond to light by changing the period of their circadian pacemaker (in addition to shifting phase). The authors suggest that also human circadian systems take advantage of this possibility and that their pacemakers respond to light by shifting phase and changing period. As a consequence of this postulated mechanism, the simulations demonstrate that the period of the pacemaker under normally entrained conditions is 24 h. The maximum accuracy corresponds to a day-to-day standard deviation of the time of phase 0 of circa 15 min. This is considerably more accurate than the light signal humans usually perceive.

  • Brain Research

    Effects of changes in glucose concentration on synaptic plasticity in hippocampal slices

    Amer Kamal, Kamiel Spoelstra, Geert Jan Biessels, Ivan J.A. Urban, Willem Hendrik Gispen

    The effects of a low or high concentration of glucose in the perfusion medium on synaptic activity and plasticity were studied in hippocampal slices from rats. Low-glucose medium depressed the field excitatory post-synaptic potentials (fEPSP) significantly, whereas high-glucose medium had little effect on the fEPSP. Tetanization of the afferent fibres elicited significant potentiation (LTP) of synaptic activity irrespective of the glucose concentration in the medium. This may indicate that LTP induction does not depend on optimal neural transmission. Paired-pulse facilitation (PPF) experiments showed that the medium glucose concentration did not significantly influence potentiation of the second response.

  • Canadian Journal of Zoology

    Effects of food abundance and wind on the use of tree lines by an insectivorous bat, Pipistrellus pipistrellus

    B. Verboom, Kamiel Spoelstra

    We tested the hypotheses that the distance bats fly from tree lines depend on food abundance and protection from wind. We monitored the activity of pipistrelle bats (Pipistrellus pipistrellus) and measured insect abundance and wind speed and direction at fixed distances up to 50 m from tree lines. We compared bat behaviour in different situations: with and without wind and with low and high insect abundances in adjacent open areas. In all situations, pipistrelle bats' activity decreased with increasing distance from the tree line. Within nights, we found no effect of wind speed on bat activity (sound recorded per 5 min) on the leeward side of the tree lines. Between nights, however, bats concentrated their activities closer to the tree lines at high wind speeds or angles of incidence of wind from 45°to 90°. A significant relationship between bat and insect abundances was found only when the tree line was bordered by insect-rich grassland. Since wind and insect abundance only partly explained the distances bats flew from tree lines, two alternative explanations, namely predator avoidance and the use of tree lines as acoustic landmarks, are discussed. Pipistrelle bats using a double row of trees as a commuting route at dusk flew mainly between the tree lines, regardless of insect abundance or wind speed. It is argued that predator avoidance explains this behaviour, being a constraint on movements of bats at relatively high light levels. At high wind speeds and angles of incidence greater than 45°, the proportion of pipistrelle bats commuting on the leeward side of the tree lines increased.


Projects & collaborations


  • Artificial light

    Project 2016–Present
    Nocturnal illumination leads to a permanent disturbance of natural habitats and there is accumulating evidence for – often negative – impact of artificial light in an increasing number of species.
    experimental setup
  • BioClock

    Project 2021–2027
    Our night sky is heavily light-polluted which has a far-reaching impact on our ecosystem, changing daily and seasonal timing of a multitude of organisms we share our environment with. At the NIOO-KNAW, we team up with ecologists and chronobiologists all across the Netherlands to restore healthy rhythms for ourselves and in our natural environment.