Food finding : on the trail to successful reproduction in migratory geese

Eten lijkt een vanzelfsprekende bezigheid, maar in de natuur is eerder het omgekeerde het geval. Dit omdat voedsel schaars is of omdat tijd ontbreekt om voedsel te zoeken. Maar hoe is de dagelijkse strijd om voedsel zichtbaar te maken? Dit proefschrift laat zien dat individuen verschillen in hoe succesvol ze zijn om voldoende voedsel te vinden. Het laat ook zien dat geringe verschillen in succes bij het voedsel zoeken grote gevolgen kunnen hebben voor de kansen om nakomelingen te krijgen en om te overleven. Het onderzoek werd verricht aan ganzen, planteneters die vaak letterlijk in hun voedsel lijken te waden, en die we op het eerste gezicht niet met voedselgebrek associëren. ... Zie: Samenvatting

Identifying individual polar bears at safe distances:A test with captive animals

The need to recognise individuals in population and behavioural studies has stimulated the development of various identification methods. A commonly used method is to employ natural markers to distinguish individuals. In particular, the automated processing of photographs of study animals has gained interest due to the speed of processing and the ability to handle a high volume of records. However, automated processing requires high-quality photographs, which means that they need to be taken from a specific angle or at close distances. Polar bears Ursus maritimus, for example, may be identified by automated analysis of whisker spot patterns. However, to obtain photographs of adequate quality, the animals need to be closer than is usually possible without risk to animal or observer. In this study we tested the accuracy of an alternative method to identify polar bears at further distances. This method is based on distinguishing a set of physiognomic characteristics, which can be recognised from photographs taken in the field at distances of up to 400 m. During five trials, sets of photographs of 15 polar bears from six zoos, with each individual bear portrayed on different dates, were presented for identification to ten test observers. Among observers the repeatability of the assessments was 0.68 (SE 0.011). Observers with previous training in photogrammetric techniques performed better than observers without training. Experience with observing polar bears in the wild did not improve skills to identify individuals on photographs. Among the observers with photogrammetric experience, the rate of erroneous assessment was on average 0.13 (SE 0.020). For the inexperienced group this was 0.72 (SE 0.018). Error rates obtained with automated whisker spot analysis were intermediate (0.26-0.58). We suggest that wildlife studies will benefit from applying several identification techniques to collect data under different conditions

Young birds switch but old birds lead : how barnacle geese adjust migratory habits to environmental change

This research was funded by a grant from the Netherlands Organization for Scientific Research awarded to TO (ref 019.172EN.011).Long-distance migratory animals must contend with global climate change, but they differ greatly in whether and how they adjust. Species that socially learn their migration routes may have an advantage in this process compared to other species, as learned changes that are passed on to the next generation can speed up adjustment. However, evidence from the wild that social learning helps migrants adjust to environmental change is absent. Here, we study the behavioral processes by which barnacle geese (Branta leucopsis) adjust spring-staging site choice along the Norwegian coast, which appears to be a response to climate change and population growth. We compared individual-based models to an empirical description of geese colonizing a new staging site in the 1990s. The data included 43 years of estimated annual food conditions and goose numbers at both staging sites (1975–2017), as well as annual age-dependent switching events between the two staging sites from one year to the next (2000–2017). Using Approximate Bayesian Computation, we assessed the relative likelihood of models with different “decision rules”, which define how individuals choose a staging site. In the best performing model, individuals traveled in groups and staging site choice was made by the oldest group member. Groups normally returned to the same staging site each year, but exhibited a higher probability of switching staging site in years with larger numbers of geese at the staging site. The decision did not depend on food availability in the current year. Switching rates between staging sites decreased with age, which was best explained by a higher probability of switching between groups by younger geese, and not by young geese being more responsive to current conditions. We found no evidence that the experienced foraging conditions in previous years affected staging site choice. Our findings demonstrate that copying behavior and density-dependent group decisions explain how geese adjust their migratory habits rapidly in response to changes in food availability and competition. We conclude that considering social processes can be essential to understand how migratory animals respond to changing environments.Publisher PDFPeer reviewe

Characteristics of Young Adults Sentenced with Juvenile Sanctions in the Netherlands

Since 1 April 2014, young adults aged 18 up to and including 22 years can be sentenced with juvenile sanctions in the Netherlands. This legislation is referred to as ‘adolescent criminal law’ (ACL). An important reason for the special treatment of young adults is their over-representation in crime. The underlying idea of ACL is that some young adult offenders are less mature than others. These young adults may benefit more from pedagogically oriented juvenile sanctions than from the deterrent focus of adult sanctions. Little is known, however, about the characteristics of the young adults sentenced with juvenile sanctions since the implementation of ACL. The aim of this study is to gain insight into the demographic, criminogenic and criminal case characteristics of young adult offenders sentenced with juvenile sanctions in the first year after the implementation of ACL. A cross-sectional study was conducted using a juvenile sanction group and an adult sanction group. Data on 583 criminal cases of young adults, sanctioned from 1 April 2014 up to March 2015, were included. Data were obtained from the Public Prosecution Service, the Dutch Probation Service and Statistics Netherlands. The results showed that characteristics indicating problems across different domains were more prevalent among young adults sentenced with juvenile sanctions. Furthermore, these young adults committed a greater number of serious offences compared with young adults who were sentenced with adult sanctions. The findings of this study provide support for the special treatment of young adult offenders in criminal law as intended by ACL