Kees Schreven

Kees Schreven PhD



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)

Publications not mentioned in publications tab:

International journals:
Schreven K.H.T. & Lehikoinen A.E. 2020. Arctic Terns attacking a leucistic Barnacle Goose near Longyearbyen, Svalbard: an explanation for the high local leucism frequency? Goose Bulletin 26: 2-6.…
Schreven K.H.T. 2020. Can Starlings imitate a Blackbird's song upon seeing a silent Blackbird? Fróðskapparit 65-66: 163-166 (with Faroese summary).
Schreven K.H.T., Dooley J.L., Leafloor J.O. & Tijsen W. 2020. Records of a 'crested' Lesser Snow Goose and Brent Goose in the wild, and a discussion of previous records in relation to environmental pollution. Goose Bulletin 25: 6-10.…
Schreven K.H.T. 2020. Lanceolated Warbler on Hornøya, Svalbard. Dutch Birding 42(3): 175-179.
Schreven K.H.T. 2020. Arctic Skuas caring for Common Eider duckling. British Birds 113(4): 235-238.…
Schreven K.H.T. 2020. Blue Tit feeding a Great Tit brood. British Birds 113(3): 182.
Schreven K.H.T. & Hammer S. 2019. Primary moult of Great Skuas on the breeding grounds, with special attention to the Faroe Islands. Sula 27: 1-16.
Schreven K.H.T. & Lehikoinen A.E. 2019. A 'crested' Pink-footed Goose observed in Norway, and possible explanations why crested waterfowl are rare in the wild. Goose Bulletin 24: 4-7.…
Schreven K.H.T. & Kangassalo K. 2019. Male Blue Tit feeding an injured female. British Birds 112(1): 49-50.

National journals
Thissen J.B.M., Schreven K.H.T., van der Horst Y., Müskens G.J.D.M. & Zollinger R. 2023. Studies of home range of a female Goshawk (Accipiter gentilis) in the breeding season in Reichswald, Kleve with GPS telemetry. Charadrius 58: (in German with English summary)
Schreven K.H.T. & van der Horst Y.H.T.H. 2022. The road takes its toll: traffic victims in relation to characteristics of species, environment and a fauna passage. Limosa 95(1): 3-27 (in Dutch with English summary)
Schreven K.H.T. 2016. Predation by raptors and mammals on a large flock of Common Starlings Sturnus vulgaris at a night roost in a reedbed. De Takkeling 24(2): 102-110 (in Dutch with English summary)
Van Turnhout C., Nienhuis J., Majoor F., Ottens G., Schreven K. & Schoppers J. 2016. Breeding performance of Common Starlings Sturnus vulgaris in the Netherlands. Limosa 89(2): 37-45 (in Dutch with English summary)
Schreven K. & van der Horst, Y. 2016. A Sparrowhawk Accipiter nisus nestling without yellow carotenoid pigmentation. Limosa 89(2): 23-26 (in Dutch with English summary)
Müskens G.J.D.M., Thissen J.B.M., van der Horst Y., Schreven K.H.T., Visser D., Zollinger R. 2015. Extremely high raptor breeding densities in the Reichswald Forest near Kleve. Charadrius 51(2): 63-79 (in German with English summary)…
Schreven K.H.T., Mooijman P.J.W. & Helder J. 2015. The parasitic nematode Synhimantus laticeps, identified using 18S rDNA sequencing, in the stomach of an emaciated Sparrowhawk Accipiter nisus. De Takkeling 23(2): 134-140 (in Dutch with English summary)
Klaassen R., Klaassen H., Berghuis A., Berghuis M., Schreven K., van der Horst, Y., Verkade, H. & Kearsley, L. 2014. Migration routes and wintering areas of Dutch Common Swifts Apus apus revealed using geolocators. Limosa 87(4): 173-181 (in Dutch with English summary)
Schreven K.H.T. 2014. An airgun pellet in the food of a Northern Goshawk Accipiter gentilis, in the context of hunting and lead poisoning. De Takkeling 22(3): 225-229 (in Dutch with English summary)
Schreven K.H.T. 2012. Egg-capping: a case in Common Buzzard Buteo buteo and evolutionary aspects. De Takkeling 20(2): 126-132 (in Dutch with English summary)

Local journals
Schreven K. 2022. De Veldleeuwerik als broedvogel in Groesbeek in 2009-2022. Groesbeeks Milieujournaal 45(2): 18-24 (in Dutch)
Thissen J., van der Horst Y. & Schreven K. 2017. Weidevogelbescherming in Groesbeek 2002-2017. Groesbeeks Milieujournaal 40(3): 8-14 (in Dutch)
Schreven K. 2017. Verspreiding en trends van de Veldleeuwerik als broedvogel in Groesbeek in 2009-2016. Mourik 43(1): 26-36 (in Dutch)
Schreven K. 2012. Staatssecretaris Bleker, de jagers, en de boeren. Groesbeeks Milieujournaal 35(1-2): 22-24 (in Dutch)
Schreven K. 2011. Viltkruiden en droogbloemen in Groesbeek. Groesbeeks Milieujournaal 34(4): 15-19 (in Dutch)
Schreven K. 2011. Helpgedrag bij het Waterhoen. Mourik 37(3): 103-106 (in Dutch)
Schreven K. 2010. Bekentellingen in Groesbeek: watervogels in een glaciaal bekken in de winter. Mourik 36(3): 82-92 (in Dutch)



Peer-reviewed publicaties

  • Animal Biotelemetry

    Effects of capture and GPS-tagging in spring on migration timing and reproduction in Pink-footed geese Anser brachyrhynchus

    Kees Schreven, Jesper Madsen, Bart A. Nolet

    Background: GPS-transmitters enable detailed study of animal behaviour but may impact the animals. Impacts vary from short-term stress and habituation to longer-term effects on e.g., migration and reproduction. To study impacts, ideally, true controls (i.e., uncaptured or untagged animals) are used, but unbiased assessments of their migration timing and breeding performance are challenging, especially in remote areas. Alternatively, quasi-controls can be used: individuals tagged longer ago, or the same tagged individuals but in later years. Quasi-controls reveal tagging effects that differ between the first and following years. Results: We captured Pink-footed geese (Anser brachyrhynchus) in spring and summer and deployed GPS-transmitter neckbands. In spring, geese were caught with cannon or clap nets on stopovers in Norway and Finland, 2 weeks before departure to breeding areas in Svalbard and Novaya Zemlya. In summer, geese were rounded up during wing moult in Svalbard. First, we compared geese tagged recently in spring with geese tagged in spring or summer 1–4 years prior. Newly tagged geese migrated significantly later, by 2 days, than previously tagged geese, both at departure from the spring stopover and arrival to the breeding grounds, while migration duration did not differ. Breeding propensity and laying date did not differ, but nesting success tended to be lowered, resulting in a significantly lower annual probability to produce hatchlings in recently tagged geese than in previously tagged geese. Second, within individuals tagged in spring, spring migration advanced in their next year, suggesting delay in their first spring. This was likely not an ageing effect, as geese tagged in summer showed no advancing spring migration timing over the years. Third, in Svalbard, observed brood sizes of geese tagged in summer and untagged geese did not differ 1 year after tagging. Conclusions: The capture and GPS-tagging of geese 2 weeks before spring departure delayed their spring migration and lowered their probability to produce hatchlings in that year. These effects lasted longer than previously reported week-long effects of GPS-tagging on time budgets in summer and of neck-banding on spring body condition. Additional study is needed to evaluate longer-term or permanent effects which remain undetected with quasi-controls.
  • Hydrobiologia

    Are increasing roosting waterbird numbers responsible for eutrophication of shallow lakes? Examples from a Danish Ramsar site

    Preben Clausen, Torben L. Lauridsen, Claus Lunde Pedersen, Henrik Haaning Nielsen, Erik Jeppesen, Martin Søndergaard, Kees Schreven, Bart A. Nolet, Jesper Madsen, Anthony D. Fox
    The Water Framework Directive (WFD) requires actions from European Union Member States to reduce external nutrient loading in lakes of moderate/poor/bad ecological status and restore their good ecological status. Several poor-quality Danish lakes have been exempted from WFD criteria (and more proposed), due to suspected major imported nutrient contributions from waterbirds, without supporting evidence. Here, we estimated relative nutrient contributions from increasing numbers of roosting waterbirds compared to total nutrient loadings in four brackish lakes (43–491 ha) at an internationally important Ramsar site/EU Birds Directive Special Protection Area. Combining night- and daytime counts of roosting numbers of the most numerous species with intake and faecal output models, we estimated roosting birds (mostly geese) contributed 0.2–0.4% of all N inputs (0.3–1.2 kg N/ha/year) and 0.6–2.0% of all P inputs (0.04–0.12 kg P/ha/year) in three lakes (one of which has been proposed exempted from WFD criteria), but potentially as high as 14% and 76%, respectively, at a fourth clearwater lake without direct inflow or outlets. These results confirm the need for case-by-case assessments of avian nutrient import relative to total nutrient balance before exempting lakes from WFD conditions due to supposed natural loading from waterbirds.
  • Ecosphere

    Snowmelt progression drives habitat selection and vegetation disturbance by an Arctic avian herbivore

    Isabell Eischeid, Jesper Madsen, Rolf A. Ims, Bart A. Nolet, Åshild Ø. Pedersen, Kees Schreven, Eeva M. Soininen, Nigel G. Yoccoz, Virve T. Ravolainen
    Arctic tundra vegetation is affected by rapid climatic change and fluctuating herbivore population sizes. Broad-billed geese, after their arrival in spring, feed intensively on belowground rhizomes, thereby disturbing soil, mosses, and vascular plant vegetation. Understanding of how springtime snowmelt patterns drive goose behavior is thus key to better predict the state of Arctic tundra ecosystems. Here, we analyzed how snowmelt progression affected springtime habitat selection and vegetation disturbance by pink-footed geese (Anser brachyrhynchus) in Svalbard during 2019. Our analysis, based on GPS telemetry data and field observations of geese, plot-based assessments of signs of vegetation disturbance, and drone and satellite images, covered two spatial scales (fine scale: extent 0.3 km2, resolution 5 cm; valley scale: extent 30 km2, resolution 10 m). We show that pink-footed goose habitat selection and signs of vegetation disturbance were correlated during the spring pre-breeding period; disturbances were most prevalent in the moss tundra vegetation class and areas free from snow early in the season. The results were consistent across the spatial scales and methods (GPS telemetry and field observations). We estimated that 23.4% of moss tundra and 11.2% of dwarf-shrub heath vegetation in the valley showed signs of disturbance by pink-footed geese during the study period. This study demonstrates that aerial imagery and telemetry can provide data to detect disturbance hotspots caused by pink-footed geese. Our study provides empirical evidence to general notions about implications of climate change and snow season changes that include increased variability in precipitation.
  • Journal of Animal Ecology

    Earlier springs increase goose breeding propensity and nesting success at Arctic but not at temperate latitudes

    Chiel Boom, Kees Schreven, Nelleke Buitendijk, Sander Moonen, Bart A. Nolet, Götz Eichhorn, Henk P. van der Jeugd, Thomas Lameris

    Intermittent breeding is an important tactic in long-lived species that trade off survival and reproduction to maximize lifetime reproductive success. When breeding conditions are unfavourable, individuals are expected to skip reproduction to ensure their own survival. Breeding propensity (i.e. the probability for a mature female to breed in a given year) is an essential parameter in determining reproductive output and population dynamics, but is not often studied in birds because it is difficult to obtain unbiased estimates. Breeding conditions are especially variable at high latitudes, potentially resulting in a large effect on breeding propensity of Arctic-breeding migratory birds, such as geese. With a novel approach, we used GPS-tracking data to determine nest locations, breeding propensity and nesting success of barnacle geese, and studied how these varied with breeding latitude and timing of arrival on the breeding grounds relative to local onset of spring. Onset of spring at the breeding grounds was a better predictor of breeding propensity and nesting success than relative timing of arrival. At Arctic latitudes (>66° N), breeding propensity decreased from 0.89 (95% CI: 0.65–0.97) in early springs to 0.22 (95% CI: 0.06–0.55) in late springs, while at temperate latitudes, it varied between 0.75 (95% CI: 0.38–0.93) and 0.89 (95% CI: 0.41–0.99) regardless of spring phenology. Nesting success followed a similar pattern and was lower in later springs at Arctic latitudes, but not at temperate latitudes. In early springs, a larger proportion of geese started breeding despite arriving late relative to the onset of spring, possibly because the early spring enabled them to use local resources to fuel egg laying and incubation. While earlier springs due to climate warming are considered to have mostly negative repercussions on reproductive success through phenological mismatches, our results suggest that these effects may partly be offset by higher breeding propensity and nesting success.
  • Oecologia

    Year-round activity levels reveal diurnal foraging constraints in the annual cycle of migratory and non-migratory barnacle geese

    Chiel Boom, Thomas Lameris, Kees Schreven, Nelleke Buitendijk, Sander Moonen, Peter De Vries, Elmira M. Zaynagutdinova, Bart A. Nolet, Henk P. van der Jeugd, Götz Eichhorn
    Performing migratory journeys comes with energetic costs, which have to be compensated within the annual cycle. An
    assessment of how and when such compensation occurs is ideally done by comparing full annual cycles of migratory and
    non-migratory individuals of the same species, which is rarely achieved. We studied free-living migratory and resident bar-
    nacle geese belonging to the same flyway (metapopulation), and investigated when differences in foraging activity occur, and
    when foraging extends beyond available daylight, indicating a diurnal foraging constraint in these usually diurnal animals.
    We compared foraging activity of migratory (N = 94) and resident (N = 30) geese throughout the annual cycle using GPS-
    transmitters and 3D-accelerometers, and corroborated this with data on seasonal variation in body condition. Migratory
    geese were more active than residents during most of the year, amounting to a difference of over 370 h over an entire annual
    cycle. Activity differences were largest during the periods that comprised preparation for spring and autumn migration.
    Lengthening days during spring facilitated increased activity, which coincided with an increase in body condition. Both
    migratory and resident geese were active at night during winter, but migratory geese were also active at night before autumn
    migration, resulting in a period of night-time activity that was 6 weeks longer than in resident geese. Our results indicate
    that, at least in geese, seasonal migration requires longer daily activity not only during migration but throughout most of the
    annual cycle, with migrants being more frequently forced to extend foraging activity into the night.
  • 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 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.
  • 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 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.
  • 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.
  • 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.
  • 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.
  • 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.

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