Human activities and recent changes in sanitary regulations are currently shaping the availability of carrion resources across ecosystems. How changes in regulations influence demographic parameters in avian scavengers is still poorly known. We combine photographic observations gathered by citizens and observational data from research projects in northern Spain to examine if the age structure of Eurasian Griffon Vulture (Gyps fulvus) populations at different trophic resources (natural randomly-distributed carcasses, predictable resources [supplementary feeding sites and farms], and landfills) varied in relation to modifications of sanitary regulations from 2004 onwards. We found that the proportion of immature birds increased significantly after the introduction of new European sanitary regulations allowing farmers to dispose of livestock carcasses in the field, rather than incinerating them. Also, we found that the age structure varied significantly between food resources, such that we detected a higher fraction of immatures at landfills, as well as in sites where carrion was highly clumped. These findings reveal that loss of natural randomness in carrion availability may elicit age-dependent effects on the spatial distribution of the vultures at the mesoscale which may ultimately affect population structure. Our findings shed light on challenges on how to manage food subsidies to preserve avian scavenger populations in an increasingly anthropized world.Les apports alimentaires déterminent la structure d'âge chez un charognard aviaire au sommet de la chaîne alimentaire RÉSUMÉ. Les activités humaines et les récents changements dans la réglementation sanitaire façonnent actuellement la disponibilité des ressources en charognes dans les écosystèmes. La manière dont ces changements de réglementation influent sur les paramètres démographiques des charognards aviaires est encore mal connue. Nous avons combiné des observations photographiques recueillies par des citoyens et des données d'observation provenant de projets de recherche dans le nord de l'Espagne pour examiner si la structure d'âge des populations de Vautours fauves (Gyps fulvus) se nourrissant de ressources différentes (carcasses naturelles réparties de façon aléatoire, ressources prévisibles [sites d'alimentation supplémentaires et fermes] et décharges) a varié en fonction des modifications de la réglementation sanitaire à partir de 2004. Nous avons constaté que la proportion d'oiseaux immatures a augmenté de manière significative après l'introduction de nouveaux règlements sanitaires européens permettant aux agriculteurs d'éliminer les carcasses de bétail en les laissant dans les champs plutôt que de les incinérer. Nous avons également constaté que la structure d'âge variait de manière importante selon les ressources alimentaires : une fraction plus élevée d'immatures a été détectée dans les décharges, ainsi que dans les sites où les charognes étaient fortement concentrées. Ces résultats révèlent que la perte du caractère aléatoire naturel de la disponib...
Urbanization has reshaped ecosystems and changed natural processes, driving an intense transformation of biomes, biotic community composition and diversity. Despite the growing interest in studying urban ecology over the last decades, the consequences of these changes on species occupying these ecosystems are not yet fully understood. Trophic generalism and tolerance to human disturbance have been proposed as two key traits in the colonization of urban environments. However, most studies focused on species’ average traits, paying less attention to the potential role of inter-individual variability. Here, we examined diet specialization in urban and rural breeding pairs, as well as its relationship with individual behaviour and intraspecific competition, using the burrowing owl as a study model. Our results show that both urban and rural breeding pairs behaved as trophic specialists. The diet of burrowing owl breeding pairs followed a gradient from coleopteran- to micromammal-dominated, which is related to individual behaviour (bolder individuals consuming more coleopterans than shyer ones). Besides, pairs distant from others showed a more diverse diet than those experiencing higher levels of intraspecific competition. Models fitted separately for each habitat showed that the proportion of micromammals in the diet of urban breeding pairs was related to their behavior, while the diet of rural pairs was not affected by individual behavior but by intraspecific competition. However, despite the strong selection of tame and more explorative individuals in urban environments and the higher density they reach in this habitat type, they did not differ in their degree of diet specialization from rural conspecifics. Although it would be necessary to evaluate prey availability on a small scale, our results suggest that burrowing owl breeding pairs behave as specialists, despite the generalist character of the species, and that this specialization is not affected by the occupation of urban environments but to individual behaviour and intraspecific competition.
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