Abstract Despite widespread occurrence of seasonal sociality among animals, little is still known about the social drivers and population-level social implications of seasonal grouping behaviours, especially in birds. Here, we studied the combined effects of ecological and social factors on seasonal grouping patterns in a sedentary population of Egyptian vultures living on the Eastern Canary Islands. We focussed on the social significance of large-scale gatherings taking place outside the breeding season at a highly preferred feeding station and a nearby temporary roost. Group sizes at this feeding patch followed a strong seasonal pattern characterized by distinct monthly changes in group composition, according to sex, age and territorial status. In between reproductive periods, vulture numbers at the feeding station may reach up 50% of the total population on a single day. GPS-tracking showed that this increase in vulture numbers was in part due to a shift in foraging range towards the centre of Fuerteventura by low-ranked territorial birds breeding in remote areas. During this period, vultures may spend on average 30% of their monthly time in a social gatherings context, depending on social status. We show that seasonal grouping patterns are shaped by the complex interplay between ecological factors (reproductive constraints, resource seasonality, food predictability), age-specific traits and social competitive processes, while social attraction may be an important additional component. We propose that for facultative social foragers living in highly despotic territorial systems, collective foraging may be of particular relevance regarding the development of hierarchical social relations and maintenance of population-level social cohesion. Significance statement We show that seasonal grouping patterns in a sedentary island population of a territorial vulture are shaped by the complex interplay between ecological factors (reproductive constraints, resource seasonality, food predictability), age-specific traits and social competitive processes. We argue that vultures visit large gatherings also for social purposes. Group foraging events may be of special interest to vultures, given opportunities for rank maintenance/improvement, but also for conspecific evaluation and mate-seeking, and play an important role in the social structuring of populations. Vultures may serve as important model species to test the role of scavenging and fission–fusion social dynamics in driving the evolution of avian social cognition, or avian social complexity in general.

中文翻译：

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领土秃鹰的季节性分组动态：生态驱动因素和社会后果

摘要 尽管动物之间普遍存在季节性社会性，但人们对季节性分组行为的社会驱动因素和种群水平的社会影响知之甚少，尤其是在鸟类中。在这里，我们研究了生态和社会因素对居住在加那利群岛东部的埃及秃鹰的久坐种群的季节性分组模式的综合影响。我们专注于在繁殖季节之外在一个非常受欢迎的饲养站和附近的临时栖息地举行的大规模聚会的社会意义。在这个饲养区的群体规模遵循强烈的季节性模式，其特征是群体组成根据性别、年龄和领土状况每月发生明显的变化。在生育期之间，饲喂站的秃鹫数量可能在一天内达到总种群的 50%。GPS 跟踪显示，秃鹫数量的增加部分是由于在偏远地区繁殖的低等级领地鸟类将觅食范围向富埃特文图拉岛中心转移。在此期间，根据社会地位，秃鹫可能平均每月有 30% 的时间用于社交聚会。我们表明，季节性分组模式是由生态因素（生殖约束、资源季节性、食物可预测性）、特定年龄特征和社会竞争过程之间复杂的相互作用形成的，而社会吸引力可能是一个重要的附加组成部分。我们建议，对于生活在高度专制领土系统中的兼性社会觅食者，集体觅食可能与等级社会关系的发展和人口一级社会凝聚力的维持特别相关。意义声明我们表明，领土秃鹰的久坐岛屿种群的季节性分组模式是由生态因素（生殖限制、资源季节性、食物可预测性）、特定年龄特征和社会竞争过程之间复杂的相互作用形成的。我们认为秃鹫也出于社交目的而参加大型聚会。群体觅食活动可能对秃鹰特别感兴趣，因为有机会维持/提高等级，但也有机会进行同种评估和寻找配偶，并在种群的社会结构中发挥重要作用。