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Transhumance is the traditional livestock practice consisting in the seasonal movement of herds between winter and summer pastures. Transhumance have important effects on the ecosystem functions from local to regional scales. Here, we 1) explored the relationship of vultures to transhumant herds, and 2) tested whether there is a shift on the use of space by vultures due to the decline of transhumance. For that, we first assessed whether vultures follow transhumant herds in two mountain areas with transhumant tradition, Pyrenees (Spain) and Andes (Argentina). Second, we compared both systems to determine whether the impact of transhumance on the use of space of vultures is greater in the area where transhumance is still relevant (Andes) than where this activity is in decline (Pyrenees). For this purpose, we analyzed the use of the summer pastures made by 50 griffon vultures (Gyps fulvus) and 18 Andean condors (Vultur gryphus), as assessed by GPS tracking. Our findings showed that both species respond to transhumance by making greater use of summer pastures when herds are present. A higher proportion of condors made use of summer pastures than griffons, and condors individually made a more intense use of it than griffons. Differences could be explained by the fact that transhumance in the Andes is still important while in the Pyrenees is declining and the amount of carrion provided is lower. Given that the abandonment of traditional activities is a phenomenon underway, it is urgent to evaluate the effects it will have on biodiversity conservation. This research was funded by Comunidad de Bardenas Reales de Navarra and Project TRASCAR (RTI2018-099609-B-C21-C22; Junta de Andalucía (P18-RT-1321); Spanish Ministry of Economy and Competitiveness and EU/FEDER). This study also forms part of the project DIGITALPAST (TED2021-130005B-C21-C22), MCIN/AEI/ 10.13039/501100011033 with funding from Plan NextGenerationEU. We also thank Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), the Agencia Nacional de Promoción Científica y Tecnológica, PICT 2014-0725, PICT 2021-I-A-00484, the Universidad Nacional del Comahue, project 04/B227 and IAATE Conservation Award). E.A. was supported by La Caixa-Severo Ochoa International PhD Program 2015; Generalitat Valenciana and European Social Fund (APOSTD/2021), and Spanish Ministry of Science, Innovation and Universities Contracts (FJC2021-047885-I). ACA was supported by Emergia contract of Junta de Andalucia, Spain. JG was supported by the Peregrin Fund.

Individual dietary variation has important ecological and evolutionary consequences. However, it has been overlooked in many taxa that are thought to have homogeneous diets. This is the case of vultures, considered merely as ‘carrion eaters’. Given their high degree of sociality, vultures are an excellent model to investigate how inter-individual transmissible behaviours drive individual dietary variation. Here, we combine GPS-tracking and accelerometers with an exhaustive fieldwork campaign to identify the individual diet of 55 griffon vultures (Gyps fulvus) from two Spanish populations that partially overlap in their foraging areas. We found that individuals from the more humanized population consumed more anthropic resources (e.g. stabled livestock or rubbish), resulting in more homogeneous diets. By contrast, individuals from the wilder population consumed more wild ungulates, increasing their dietary variability. Between sexes, we found that males consumed anthropic resources more than females did. Interestingly, in the shared foraging area, vultures retained the dietary preference of their original population, highlighting a strong cultural component. Overall, these results expand the role of cultural traits in shaping key behaviours and call for the need of including cultural traits in Optimal Foraging models, especially in those species that strongly rely on social information while foraging.

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 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 disponibilité de la charogne peut entraîner des effets dépendants de l'âge sur la répartition spatiale des vautours à l'échelle méso, ce qui peut affecter la structure de la population en fin de compte. Nos résultats mettent en lumière les défis à relever pour gérer les apports alimentaires afin de préserver les populations de charognards aviaires dans un monde de plus en plus anthropisé. Ministerio de Economía y Competitividad RTI2018-099609-BC21 Govern de las Illes Balears AAEE123/2017