Kees Schreven

Kees Schreven

PhD Student


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)




Peer-reviewed publicaties

  • 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.
  • 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.
  • 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.

Projecten & samenwerkingen