Abstract
BackgroundMigrant populations must cope not only with environmental changes in different biomes, but also with the continuous constraints imposed by human-induced changes through landscape transformation and resource patchiness. Theoretical studies suggest that changes in food distribution can promote changes in the social arrangement of individuals without apparent adaptive value. Empirical research on this subject has only been performed at reduced geographical scales and/or for single species. However, the relative contribution of food patchiness and predictability, both in space and time, to abundance and sociality can vary among species, depending on their degree of flexibility.Methodology/Principal FindingsBy means of constrained zero-inflated Generalized Additive Models we analysed the spatial distribution of two trans-Saharan avian scavengers that breed (Europe) and winter (Africa) sympatrically, in relation to food availability. In the summering grounds, the probability of finding large numbers of both species increases close to predictable feeding sources, whereas in the wintering grounds, where food resources are widespread, we did not find such aggregation patterns, except for the black kite, which aggregated at desert locust outbreaks. The comparison of diets in both species through stable isotopes revealed that their diets overlapped during summering, but not during wintering.Conclusions/SignificanceOur results suggest that bird sociality at feeding grounds is closely linked to the pattern of spatial distribution and predictability of trophic resources, which are ultimately induced by human activities. Migrant species can show adaptive foraging strategies to face changing distribution of food availability in both wintering and summering quarters. Understanding these effects is a key aspect for predicting the fitness costs and population consequences of habitat transformations on the viability of endangered migratory species.
Highlights
The distribution of key resources affects the spatial structure and the social organization of animal populations [1,2,3]
Conclusions/Significance: Our results suggest that bird sociality at feeding grounds is closely linked to the pattern of spatial distribution and predictability of trophic resources, which are induced by human activities
Bird abundance and food resource availability Egyptian vultures were detected in 20.6% of the African (n = 85)
Summary
The distribution of key resources affects the spatial structure and the social organization of animal populations [1,2,3]. Obligate migratory species are logically enforced to respond to variable conditions when moving from summering to wintering grounds Within this scenario, the lack of studies tracking the response of migrant organisms to large-scale changes in the degree of heterogeneity in the spatial distribution of food resources is striking. It seems important to discern whether migrant birds have flexible responses to variations in environmental conditions between summering and wintering grounds, such as changes in the availability of food resources This information may be useful in understanding large-scale variability in the role of limiting factors on the viability of populations of migrant species of conservation concern [18,19]. Theoretical studies suggest that changes in food distribution can promote changes in the social arrangement of individuals without apparent adaptive value Empirical research on this subject has only been performed at reduced geographical scales and/or for single species. The relative contribution of food patchiness and predictability, both in space and time, to abundance and sociality can vary among species, depending on their degree of flexibility
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