Abstract
Partial migration, whereby some individuals migrate and some do not, is relatively common and widespread among animals. Switching between migration tactics (from migratory to resident or vice versa) occurs at individual and population levels. Here, we describe for the first time the movement ecology of the largest wintering population of Egyptian Vultures (Neophron percnopterus) in south-west Europe. We combined field surveys and GPS tracking data from December to February during four wintering seasons (2014–2018). The wintering population consisted on average of 85 individuals (range 58–121; 76% adults and 24% subadults). Individuals were counted at five different roosting sites located near farms, unauthorized carcass deposition sites and authorized carcass deposition sites. Our results show that vultures tend to remain close to the roosting site. Moreover, we observed that females exhibited smaller home range sizes than males, which suggests a possible differential use of food sources. Overall, birds relied more on farms than other available food resources, particularly subadult individuals which exploited more intensively these sites. Our results showed that Egyptian Vultures congregate in significant numbers at specific sites throughout the winter period in south-west Spain and that these roosting and feeding sites should be given some level of legal protection and regular monitoring. Furthermore, predictable food sources might be driving the apparent increase in the non-migratory population of Egyptian Vultures, as observed in other avian species which are also changing their migratory behavior.
Highlights
Partial migration, whereby some individuals migrate and some do not, is relatively common and widespread among animals
Little is known about how species behave in those environments during winter through the study of movement patterns across time and space and on the impacts of the utilization and availability of predictable food resources on daily movement patterns and migratory behaviour
We describe for the first time the spatial ecology and resource use of a unique Egyptian Vulture population which, contrary to the commonest migratory pattern, winters in south-west Europe, by means of the combination of field surveys and telemetry information
Summary
Whereby some individuals migrate and some do not, is relatively common and widespread among animals. The coexistence of these migration behaviours appears to be driven by individual asymmetries in variables such as sex, age, body size, as well as by environmental conditions[5] Switching between these two strategies could occur at population and individual level, depending on season[6], migration direction[7], route, timing[8], and distance to wintering g rounds[9]. Thanks to the emerging use and rapid improvements in telemetry techniques[19], we are able to determinate variations in migratory s trategies[20], and disentangle interactions between animals and their abiotic and biotic e nvironment[21] The integration of these techniques with traditional approaches (e.g., population monitoring) could help to better understand which factors underlie ecological and evolutionary processes in migration ecology and integrate them in conservation and management decisions. RUFs, which basically consist on a multiple regression analysis that accounts for spatial and temporal autocorrelation of tracking d ata[24], are a reliable method to (1) define the fidelity to a site according to space use and sites of ecological significance in the life history of a nimals[26]; (2) check availability and distribution of r esources[27]; and (3) to improve inference on the spatial factors influencing behaviour[28]
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