Kees Schreven

Kees Schreven

PhD Student
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Visiting Address

Droevendaalsesteeg 10
6708 PB Wageningen

+31 (0) 317 47 34 00

The Netherlands


I study long-distance range expansion in Pink-footed Geese as mechanism to cope with advancing spring by climate change in the Arctic.


My research at NIOO focuses on dispersal as mechanism to cope with climate change. In Svalbard, Pink-footed Geese (Anser brachyrhynchus) traditionally breed in the west, whereas nowadays also the east (Edgeoya) becomes snow-free early enough in the season to serve as breeding habitat. Pink-footed Geese have recently colonized this area, and we expect them to be better matched with the local food pulse than geese on traditional grounds, resulting in higher fitness. We also investigate to what extent the annual cycle differs between geese of both areas in terms of energy and time budgets and migration timing and routes, and whether geese of both areas are genetically differentiated. We will test aggression, docility and stress resistance during handling as measures of personality to see if personality may have played a role in the colonization process.

I did my Bachelor at Wageningen Universtiy focusing on Ecology and Biodiversity, with a thesis on Age- and density-dependent breeding success of Goshawks (at NIOO, A.J. van Noordwijk, and WUR, D. Kleijn). I moved to Groningen for the Topmaster Programme Evolutionary biology, with theses on Tidal migration of mobile benthic prey of Red Knots (at NIOZ, P.J. van den Hout and T. Piersma), the Relationship of personality with early-life body mass in Blue tits (at University of Turku, J.E. Brommer and B. Class), and Sex-ratio and sexual dimorphism in chicks of Honey Buzzard (at University of Groningen, C. Both and R.G. Bijlsma). After graduation I contiued working in Turku on the blue tit personalities.

Before and throughout my studies I have joined long-term breeding biology studies on raptors and meadow birds around my home-town Groesbeek, and assisted in fieldwork with Great Skuas on the Faroe Islands (University of Glasgow, S. Hammer), and with Arctic Skuas, Red-necked Phalaropes and Barnacle geese on Tobseda, Russia (NIOO, T.K. Lameris, and IMARES, R.S.A. van Bemmelen).

I am a keen fieldwork-based ecologist, valuing a holistic view and precise and standardised observations, also leaving room to respond to unexpected phenomena. Illustrative of such attitude is this quote by Tinbergen in the sixties:

"We did not tackle the problem by systematic experimentation but by collecting incidental evidence, which is not too difficult provided one has the problem continuously in mind during watching. As a rule, Nature makes numerous experiments for us and it is amazing how much evidence on can collect if one is continuously on the alert and appreciative of the possibilities." (N. Tinbergen (1960) The Herring Gull's World, p.99)

Research groups



Peer-reviewed publications

  • Current Biology

    Rapid formation of new migration route and breeding area by Arctic geese

    Jesper Madsen, Kees Schreven, Gitte Høj Jensen, Fred A. Johnson, Leif Nilsson, Bart A. Nolet, Jorma Pessa
    Many Arctic-breeding animals are at risk from local extirpation associated with habitat constriction and alterations in phenology in their Arctic environment as a result of rapid global warming.1 Migratory species face additional increasing anthropogenic pressures along their migratory routes such as habitat destruction, droughts, creation of barriers, and overexploitation.2,3 Such species can only persist if they adjust their migration, timing of breeding, and range.4 Here, we document both the abrupt (∼10 years) formation of a new migration route and a disjunct breeding population of the pink-footed goose (Anser brachyrhynchus) on Novaya Zemlya, Russia, almost 1,000 km away from the original breeding grounds in Svalbard. The population has grown to 3,000–4,000 birds, explained by intrinsic growth and continued immigration from the original route. The colonization was enabled by recent warming on Novaya Zemlya. We propose that social behavior of geese, resulting in cultural transmission of migration behavior among conspecifics as well as in mixed-species flocks, is key to this fast development and acts as a mechanism enabling ecological rescue in a rapidly changing world.
  • Conservation Letters

    Wild goose chase:

    Andrea Kölzsch, Thomas Lameris, Gerhard J D M Müskens, Kees Schreven, Nelleke Buitendijk, Helmut Kruckenberg, Sander Moonen, Thomas Heinicke, Lei Cao, Jesper Madsen, Martin Wikelski, Bart A. Nolet
    In the present Anthropocene, wild animals are globally affected by human activity. Consumer fireworks during New Year (NY) are widely distributed in W-Europe and cause strong disturbances that are known to incur stress responses in animals. We analyzed GPS tracks of 347 wild migratory geese of four species during eight NYs quantifying the effects of fireworks on individuals. We show that, in parallel with particulate matter increases, during the night of NY geese flew on average 5–16 km further and 40–150 m higher, and more often shifted to new roost sites than on previous nights. This was also true during the 2020–2021 fireworks ban, despite fireworks activity being reduced. Likely to compensate for extra flight costs, most geese moved less and increased their feeding activity in the following days. Our findings indicate negative effects of NY fireworks on wild birds beyond the previously demonstrated immediate response.
  • Journal of Ornithology

    Neckband loss and its effect on apparent survival estimates in Greylag Geese (Anser anser): variation with season, sex and age

    Kees Schreven, Berend Voslamber
    Mark-recapture studies enable us to estimate population parameters such as survival, if marks do not impact survival and if marks are not lost. Mark loss can result from external wear and damage, but also behavioural factors may be important and could explain differences between seasons or sexes. We studied Greylag Geese (Anser anser) in eastern Netherlands, ringed with neckbands, leg bands and metal rings (912 geese), observed weekly during 1997–2019 (131,625 observations). Given the double marking and high annual resighting probabilities (neckbands: 0.974, leg rings: 0.639), we quantified neckband loss and the effect of neckbands on apparent survival, using multistate mark-recapture models. Annual neckband loss was 0.038, was higher in males (0.056) than females (0.021) and increased with years since marking, up to 0.098 for males more than 8 years after marking. Neckband loss tended to be higher during December–May than June–November, with most losses occurring in March–April. Both the higher loss in males and the peak in spring in both sexes could result from intraspecific fighting (pulling each other’s neck and neckband). Survival was underestimated in Cormack-Jolly-Seber models that did not account for neckband loss, by up to 0.096 for adult males 6–7 years after marking. Thus, ignoring neckband loss may give erroneous survival differences between sexes and seasons, and overestimate the effect of ageing on survival (i.e. senescence). We did not detect an effect of neckbands on mortality, but statistical power for this test was limited. Neckband loss, although lower nowadays than in studies of decades ago, still impacts survival estimates and should be considered in mark-recapture studies.
  • Polar Biology

    Barnacle geese Branta leucopsis breeding on Novaya Zemlya

    Thomas Lameris, Olga B. Pokrovskaya, Alexander V. Kondratyev, Yuriy A. Anisimov, Nelleke Buitendijk, Petr M. Glazov, Henk P. van der Jeugd, Christian Kampichler, Helmut Kruckenberg, Konstantin E. Litvin, Julia A. Loshchagina, Sander Moonen, Gerhard J D M Müskens, Bart A. Nolet, Kees Schreven, Henk Sierdsema, Elmira M. Zaynagutdinova, Chiel Boom

    The Russian breeding population of barnacle geese Branta leucopsis has shown a rapid increase in numbers since 1980, which has coincided with a southwest-wards breeding range expansion within the Russian Arctic. Here barnacle geese also started to occupy coastal and marsh land habitats, in which they were not know to nest on their traditional breeding grounds. While these changes have been well documented by studies and observations throughout the new breeding range of barnacle geese, observations are lacking from the traditional breeding grounds on Novaya Zemlya, as this area is remote and difficult to access. This is especially relevant given rapid climate warming in this area, which may impact local distribution and population size. We used GPS-tracking and behavioural biologging data from 46 individual barnacle geese captured on their wintering grounds to locate nest sites in the Russian Arctic and study nesting distribution in 2008–2010 and 2018–2020. Extrapolating from nest counts on Kolguev Island, we estimate the breeding population on Novaya Zemlya in 2018–2020 to range around 75,250 pairs although the confidence interval around this estimate was large. A comparison with the historical size of the barnacle goose population suggests an increase in the breeding population on Novaya Zemlya, corresponding with changes in other areas of the breeding range. Our results show that many barnacle geese on Novaya Zemlya currently nest on lowland tundra on Gusinaya Zemlya Peninsula. This region has been occupied by barnacle geese only since 1990 and appears to be mainly available for nesting in years with early spring. Tracking data are a valuable tool to increase our knowledge of remote locations, but counts of breeding individuals or nests are needed to further corroborate estimates of breeding populations based on tracking data.
  • Journal of Avian Biology

    Sea crossings of migratory pink-footed geese: seasonal effects of winds on flying and stopping behaviour

    Jan Geisler, Jesper Madsen, Bart A. Nolet, Kees Schreven
    Migratory birds may need to cross barriers such as seas, without opportunities to rest or refuel. Waterbirds, unlike land birds, can stop at sea to rest or wait for better winds and thus may be less selective for supportive winds at departure and tolerate larger drift. However, pay-offs of waiting are likely to depend on circumstances (e.g. pressure for well-timed arrival, wind availability and travelling with/without juvenile brood), thus migratory behaviour during barrier crossings is expected to differ between seasons. We studied pink-footed geese Anser brachyrhynchus crossing the Barents Sea (ca 650 km), in spring and autumn during 2018–2020, using 94 GPS-tracks of 38 individuals, with annotated ERA5 weather data. We found that 1) especially in autumn, geese selected supportive winds for departure; 2) in spring, geese experienced lower wind support and more crosswinds than in autumn, leading to 23% longer routes, 60% longer durations, 93% longer air distances and 45% higher ratios of air-to-ground distances; 3) in both seasons, geese had more tailwinds in the first part of crossings, and in spring when deviating more from the shortest route; 4) geese stopped at sea more often in spring (mean 11×) than autumn (3×), in spring during earlier stages of crossings, but in both seasons, spent half of the crossing time at sea, during which they still continued to approach their destination slowly; 5) stops at sea happened mostly in adverse winds, warmer air, higher air humidity and on calmer water and, in autumn, took longer without juvenile brood. We conclude that for migrating pink-footed geese, Arctic capital breeders, the importance of time and energy can shift en route and that seasonal differences in wind support, flying and stopping behaviour and the pressure for a well-timed arrival cause the Barents Sea to be a larger barrier in spring than in autumn.
  • Ardea

    Brood Sex Ratio in European Honey Buzzards Pernis apivorus is Related to Spring Phenology

    Kees Schreven, R.G. Bijlsma, Christiaan Both
    In sexually size-dimorphic bird species, rearing costs of sons and daughters usually differ and may be important in the evolution of offspring sex ratio adjustment. Raptors have reversed sexual size dimorphism and the smaller males are sometimes found to be overrepresented in food-poor territories or years. As a raptor with small reversed sexual dimorphism (6% in body mass), the European Honey Buzzard Pernis apivorus is expected to show little or no brood sex ratio bias in relation to environmental conditions. We molecularly sexed 311 chicks of 195 broods in and around The Netherlands, during 1996–2014. We examined which environmental factors explained brood sex ratio variation best. Overall, sex ratio was not biased (all nests pooled: 50.8% females) but more females were produced in years when on average Honey Buzzards bred earlier (32% sex ratio change over a ten-day range in annual mean laying date). Within-year laying date variation, hatching order, abundance of wasp (Vespinae) nests (main food source) and summer weather did not explain sex ratio variation. In the Veluwe and Drenthe (1974–2014), Honey Buzzards laid eggs earlier when the spring was warmer, which resulted in a c. 9-day advance in laying date over 40 years. As warm spring weather was also a predictor of a higher density of wasp colonies, we expected female chicks to benefit more from growing up in wasp-rich years than males, if the sex ratio biases were adaptive. However, this differential growth benefit was not noticeable in chick body mass; chick body mass was best explained by negative effects of relative laying date (within a year) and hatching order. The potential benefit for female nestlings (compared to males) of growing up in years with warm springs, when egg laying occurs early and wasp colonies are more abundant, remains unknown.
  • Animal Biotelemetry

    Nesting attempts and success of Arctic-breeding geese can be derived with high precision from accelerometry and GPS-tracking

    Kees Schreven, Christian Stolz, Jesper Madsen, Bart A. Nolet
    Sensors, such as accelerometers, in tracking devices allow for detailed bio-logging to understand animal behaviour, even in remote places where direct observation is difficult. To study breeding in birds remotely, one needs to understand how to recognize a breeding event from tracking data, and ideally validate this by direct observation. We tagged 49 adult female Pink-footed Geese (Anser brachyrhynchus) with transmitter neckbands in Finland in spring of 2018 and 2019, and in Svalbard in summer 2018, and validated inferences from tracking by field observations of nesting sites and family status in 2018-2020 (54 spring-summer tracks). We estimated nesting locations by taking the median coordinates of GPS-fixes at which the goose was motionless (overall dynamic body acceleration, ODBA<1) on days with a daily median ODBA<1, which approached the real nesting locations closely (within 1.6-3.7 m, n=6). The start of nesting was defined as the first day on which the goose spent >75% of time within 50 m of the nest, because nest site attendances steeply increased within one day to above this threshold. Nesting duration (number of consecutive days with >75% nest site attendance) ranged between 3-44 days (n=28), but was 30-34 days in confirmed successful nests (n=9). The prolonged nesting of 39-44 days (n=3) suggested incubation on unhatchable egg(s). Nest losses before hatching time occurred mostly in day 3-10 and 23-29 of nesting, periods with an increased frequency of nest site recesses. As alternative method, allowing for non-simultaneous GPS and accelerometer data, we show that nesting days were classified with 98.6% success by two general characteristics of breeding: low body motion (daily median ODBA) and low geographic mobility (daily SD of latitude). Median coordinates on nesting days approached real nest sites closely (within 0.8-3.6 m, n=6). When considering only geographic mobility (allowing for GPS data only) nesting locations were similarly accurate, but some short nesting attempts were undetected and non-breeding tracks misclassified. We show that nesting attempts, as short as 3 days, and nesting success can be detected remotely with good precision using GPS-tracking and accelerometry. Our method may be generalized to other (precocial) bird species with similar incubation behaviour.
  • Wildfowl

    Effects of capture and marking on the behaviour of moulting Pink-footed Geese Anser brachyrhynchus on Svalbard

    Kevin Kuhlmann Clausen, Kees Schreven, Jesper Madsen
    Tracking of individuals is increasingly being used in waterfowl research. However, the effects of capture and tags on waterfowl welfare and ecology are poorly understood and too rarely reported. In this paper, time budget data are used to investigate the behavioural effects of capture and marking on moulting and brood-rearing Pink-footed Geese Anser brachyrhynchus on their arctic breeding grounds. The study compares the prevalence of self-maintenance and foraging time for unringed/uncaptured birds, male birds marked with standard neck collars and female birds marked with heavier GPS collars, and reports on the reduction through time in the pecking behaviour directed towards these markers. Results indicate that capture and marking substantially altered behaviour of marked birds in the days immediately after capture, but also that this effect faded quickly and was not discernible six days after marking. Proportions of time spent preening during foraging bouts indicated that, in the first six days, GPS-collared birds were significantly more affected (time preening c. 12%) than birds ringed with standard neck collars (c. 3%). Both groups showed higher proportions of self-maintenance type behaviours than unringed birds of the same sex (time preening < 1%). The probability of an individual goose pecking its marker during an observation period was initially high for GPS-collared birds (c. 65%), but decreased substantially to reach c. 2% by 11 days after capture. Our study indicates that, after an initial period of discomfort, neck collars and GPS collars are suitable for studying the behaviour of individual geese.
  • Bird Study

    Tail feather elongation in Great Skuas Stercorarius skua: a sexual ornament signalling individual quality?

    Kees Schreven, Sjúrður Hammer
    Capsule – In breeding Great Skuas on Skúvoy, Faroe Islands, central tail feather elongation was longer in males than females and was related to head size, laying date, egg volume, diet composition, and only in males also the tendency to incubate the clutch.
    Aims – Sexual ornaments, such as elongated tail feathers, allow birds to attract conspecifics of the opposite sex. In skuas, the smaller species have clearly elongated central tail feathers, while in the larger species, the elongation is marginal. We evaluate here if the modest elongation of the central tail feathers in Great Skuas is associated with ecological factors and thus could still function as a social signal.
    Methods and results – We caught 47 breeding Great Skuas on their nests on Skúvoy, Faroe Islands in 2013 and found that the central tail feathers were more elongated in males (mean 15.2 mm, n=20) than females (11.3 mm, n=27). This sexual dimorphism persisted when corrected for body size, as males are smaller than females. In both sexes, longer tail feather elongation was associated with a shorter head, an earlier laying date, and a higher bird-based proportion in the pair’s diet, while no spatial patterns were found. Moreover, during our catching attempts, males with a longer tail feather elongation were quicker back at the nest to incubate the clutch. Egg volume, but not chick body condition, increased with parent tail feather elongation. In a model including laying date, head size, and diet, only laying date persisted as significant predictor of the tail feather elongation, as earlier laying birds had shorter heads and ate more birds.
    Conclusion – We argue that the modest tail feather elongation in Great Skuas may signal individual quality for both sexes, and in males specifically also the nest attentiveness, even though this trait may seem ecologically irrelevant at first glance.
  • Auk

    Contrasting effects of the onset of spring on reproductive success of Arctic-nesting geese

    Bart A. Nolet, Kees Schreven, Chiel Boom, Thomas Lameris
    Breeding output of geese, measured as the proportion of juveniles in autumn or winter flocks, is lower in years with a late onset of spring in some species, but higher in at least one other species. Here we argue this is because the timing of spring affects different stages of the reproductive cycle differently in different species. Because the effects on two different stages are opposite, the combined effects can result in either a positive or a negative overall effect. These stages are the pre-laying, laying and nesting phase on the one hand, and the hatchling, fledgling and juvenile phase on the other hand. The first phase is predominantly positively affected by an early snowmelt, with higher breeding propensity, clutch size and nest success. The second phase on the other hand is negatively affected by early snowmelt, because of a mismatch with a nutrient food peak, leading to slow gosling growth and reduced survival. We argue that recognition of this chain of events is crucial when one wants to predict goose productivity and eventually goose population dynamics. In a rapidly warming Arctic, the negative effects of a mismatch might become increasingly important.
  • Dansk Ornitologisk Forenings Tidsskrift

    Why do afternoon copulations mainly occur after the egg-laying peak date in a colony of Great Skuas on Skúvoy, Faroe Islands?

    Kees Schreven, S. Hammer
    Abstract In Great Skuas Stercorarius skua, copulations are often preceded by courtship feeding and occur in the morning and afternoon.
    We surveyed copulations in a colony of Great Skuas on Skúvoy, Faroe Islands during afternoons throughout the breeding
    season of 2013. The afternoon copulation frequency peaked 2.5 weeks after the peak in laying dates. This is unexpected because
    literature suggests that a pair copulates most frequently around a week before egg laying. As we were not able to link each copulation
    to a specific pair, several explanations are possible. First, if these afternoon copulations were pre-laying copulations, they were
    presumably mostly performed by pairs laying late in the season. A possible mechanism could be that young pairs and fish-eating
    pairs, which breed later in the season, make longer foraging trips and therefore feed their mate, and thus copulate, later in the day.
    These copulations may also reflect an increased copulation rate of young pairs, to strengthen the pair bond or compensate for low
    copulation success. Alternatively, if these copulations were post-laying copulations, they may be a response to mate feeding that
    continues during the incubation phase, and may strengthen the pair bond. We argue that potential individual and population differences
    should be taken into account when describing copulation behaviour at the species level.

Projects & collaborations