TY - JOUR A1 - Rotics, Shay A1 - Kaatz, Michael A1 - Resheff, Yehezkel S. A1 - Turjeman, Sondra Feldman A1 - Zurell, Damaris A1 - Sapir, Nir A1 - Eggers, Ute A1 - Flack, Andrea A1 - Fiedler, Wolfgang A1 - Jeltsch, Florian A1 - Wikelski, Martin A1 - Nathan, Ran T1 - The challenges of the first migration: movement and behaviour of juvenile vs. adult white storks with insights regarding juvenile mortality JF - Journal of animal ecology : a journal of the British Ecological Society N2 - 1. Migration conveys an immense challenge, especially for juvenile birds coping with enduring and risky journeys shortly after fledging. Accordingly, juveniles exhibit considerably lower survival rates compared to adults, particularly during migration. Juvenile white storks (Ciconia ciconia), which are known to rely on adults during their first fall migration presumably for navigational purposes, also display much lower annual survival than adults. 2. Using detailed GPS and body acceleration data, we examined the patterns and potential causes of age-related differences in fall migration properties of white storks by comparing first-year juveniles and adults. We compared juvenile and adult parameters of movement, behaviour and energy expenditure (estimated from overall dynamic body acceleration) and placed this in the context of the juveniles’ lower survival rate. 3. Juveniles used flapping flight vs. soaring flight 23% more than adults and were estimated to expend 14% more energy during flight. Juveniles did not compensate for their higher flight costs by increased refuelling or resting during migration. When juveniles and adults migrated together in the same flock, the juvenile flew mostly behind the adult and was left behind when they separated. Juveniles showed greater improvement in flight efficiency throughout migration compared to adults which appears crucial because juveniles exhibiting higher flight costs suffered increased mortality. 4. Our findings demonstrate the conflict between the juveniles’ inferior flight skills and their urge to keep up with mixed adult–juvenile flocks. We suggest that increased flight costs are an important proximate cause of juvenile mortality in white storks and likely in other soaring migrants and that natural selection is operating on juvenile variation in flight efficiency. KW - flight KW - flight efficiency KW - juvenile mortality KW - migration KW - white stork Y1 - 2016 U6 - https://doi.org/10.1111/1365-2656.12525 SN - 0021-8790 SN - 1365-2656 VL - 85 SP - 938 EP - 947 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Zurell, Damaris A1 - Eggers, Ute A1 - Kaatz, Michael A1 - Rotics, Shay A1 - Sapir, Nir A1 - Wikelski, Martin A1 - Nathan, Ran A1 - Jeltsch, Florian T1 - Individual-based modelling of resource competition to predict density-dependent population dynamics: a case study with white storks JF - Oikos N2 - Density regulation influences population dynamics through its effects on demographic rates and consequently constitutes a key mechanism explaining the response of organisms to environmental changes. Yet, it is difficult to establish the exact form of density dependence from empirical data. Here, we developed an individual-based model to explore how resource limitation and behavioural processes determine the spatial structure of white stork Ciconia ciconia populations and regulate reproductive rates. We found that the form of density dependence differed considerably between landscapes with the same overall resource availability and between home range selection strategies, highlighting the importance of fine-scale resource distribution in interaction with behaviour. In accordance with theories of density dependence, breeding output generally decreased with density but this effect was highly variable and strongly affected by optimal foraging strategy, resource detection probability and colonial behaviour. Moreover, our results uncovered an overlooked consequence of density dependence by showing that high early nestling mortality in storks, assumed to be the outcome of harsh weather, may actually result from density dependent effects on food provision. Our findings emphasize that accounting for interactive effects of individual behaviour and local environmental factors is crucial for understanding density-dependent processes within spatially structured populations. Enhanced understanding of the ways animal populations are regulated in general, and how habitat conditions and behaviour may dictate spatial population structure and demographic rates is critically needed for predicting the dynamics of populations, communities and ecosystems under changing environmental conditions. Y1 - 2015 U6 - https://doi.org/10.1111/oik.01294 SN - 0030-1299 SN - 1600-0706 VL - 124 IS - 3 SP - 319 EP - 330 PB - Wiley-Blackwell CY - Hoboken ER -