Summary1. Geolocation by light allows for tracking animal movements, based on measurements of light intensity over time by a data-logging device ('geolocator'). Recent developments of ultra-light devices (<2 g) broadened the range of target species and boosted the number of studies using geolocators. However, an inherent problem of geolocators is that any factor or process that changes the natural light intensity pattern also affects the positions calculated from these light patterns. Although the most important factors have been identified, estimation of their effect on the accuracy and precision of positions estimated has been lacking but is very important for the analyses and interpretation of geolocator data. 2. The 'threshold method' is mainly used to derive positions by defining sunrise and sunset times from the light intensity pattern for each recorded day. This method requires calibration: a predefined sun elevation angle for estimating latitude by fitting the recorded day ⁄ night lengths to theoretical values across latitudes. Therewith, almost constant shading can be corrected for by finding the appropriate sun elevation angle. 3. Weather, topography and vegetation are the most important factors that influence light intensities. We demonstrated their effect on the measurement of day ⁄ night length, time of solar midnight ⁄ noon and the resulting position estimates using light measurements from stationary geolocators at known places and from geolocators mounted on birds. Furthermore, we investigated the influence of different calibration methods on the accuracy of the latitudinal positions. 4. All three environmental factors can influence the light intensity pattern significantly. Weather and an animal's behaviour result in increased noise in positioning, whereas topography and vegetation result in systematic shading and biased positions. Calibration can significantly shift the estimated latitudes and potentially increase the accuracy, but detailed knowledge about the particular confounding factors and the behaviour of the studied animal is crucial for the choice of the most appropriate calibration method.

Summary1. It is increasingly acknowledged that skewed adult sex ratios (ASRs) may play an important role in ecology, evolution and conservation of animals. 2. In birds, published estimates on ASRs mostly rely on mist netting data. However, previous studies suggested that mist nets or other trap types provide biased estimates on sex ratios, with males being more susceptible to capture than females. 3. We used data from a Constant Effort Site ringing scheme to show how sex ratios that are corrected for sex-and year-specific capture probabilities can be directly estimated by applying capture-recapture analysis, for example, in a Bayesian framework. 4. When capture data were pooled from the 19 years of study, we found that in the blackbird (Turdus merula) and the blackcap (Sylvia atricapilla), the observed proportions of males were 57% and 55%, respectively. However, when the observed annual proportions of males were corrected for the sex-specific capture probabilities, the proportions of males did not clearly differ from 50% in most study years, and thus, the apparent male-bias in the ASRs almost completely disappeared. 5. We propose that published estimates on ASRs in birds should be re-evaluated if based solely on observed sex ratios from mist netting studies. 6. We further propose that data from national bird ringing schemes and in particular from Constant Effort Site ringing programs can provide valuable information on ASRs, if analysed using capture-recapture models. We discuss important assumptions of those models; for example, movements that may differ between sexes should be taken into account, as well as the occurrence of transient individuals that do not hold breeding territories within a study site.

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During translocations, stress, as measured by the increase of glucocorticoids, cannot be avoided, but has been suspected to exacerbate the vulnerability to many causes of mortality after release. Therefore, measures to reduce stress have been proposed, such as keeping animals in pens before release (soft release). In this study, we investigated two open questions in translocations: (1) whether stress caused by the translocation procedure has an effect on survival; (2) whether soft release allows recovering from stress induced by capture and transportation. Hand-raised grey partridges showed a moderate adrenocortical response to transportation and kept the capacity to mount a stress response to a new acute stressor, partly by a decrease of corticosteroid-binding globulin capacity. In contrast to studies demonstrating a pervasive effect of capture and transport by virtual elimination of a proper stress response, we demonstrated a robust stress response and a return of baseline levels to pre-transport levels after 33 h of acclimatization.Possibly captive-bred birds may be less sensitive to capture and transportation than wild-caught birds. During the first month after release, birds held 33 h in release pens survived better when their corticosterone levels were lower. However, survival beyond the first month did not differ between birds held 9 or 33 h in acclimatization pens. Elevated glucocorticoids, as induced by the translocation procedure, likely affect short-term survival after release. We recommend glucocorticoid stress levels be surveyed in an appropriate subsample and minimized during translocations.

Populations of migratory birds often mix to a considerable extent in their wintering areas. Knowledge about the composition of wintering populations is highly relevant to management, not least for species such as the great cormorant Phalacrocorax carbo sinensis, prone to conflicts with human interests. However, few studies have been able to estimate long‐term changes in winter population composition. We use 30 years of ringing and recovery data (1983–2013) from all major breeding populations of cormorants in continental Europe (except the Black Sea region) to estimate partitioning probabilities (i.e. the probabilities of moving to specific wintering areas) using a Bayesian capture–mark–recovery model. Combining these results with information on breeding numbers and reproductive output in a population model, we estimate the size and composition of wintering populations in Europe and North Africa. Partitioning probabilities showed some variation over time, but were similar for first‐winter and older birds. Cormorants from the western part of the breeding range tended to winter progressively further west over time. This may be a density‐dependent response to the recent growth of more easterly breeding populations. All wintering populations grew rapidly over the study period, and their composition showed pronounced changes. All wintering populations were composed of birds from many different breeding populations, but the proportion of cormorants of more easterly origin increased markedly over time in most wintering areas. Policy implications. Cormorant wintering populations in Europe consist of mixtures of birds of different breeding origins. These mixtures are also highly variable over time. These factors reduce the chances of successfully limiting conflicts in specific wintering areas through, for example, regulation of breeding numbers in one breeding area. The dynamic nature of cormorant winter populations means that conflicts are best addressed when and where the conflict occurs, or on the scale of the entire continental population. It is unlikely that the latter will be cost‐effective and politically realistic.