Abstract

Partial migration is one of the most widespread migratory strategies among taxa. Investigating the trade-off between environmental/social factors — fitness and energetic consequences — is essential to understand the coexistence of migratory and resident behaviours. Here, we compiled field monitoring data of wintering population size and telemetry data of 25 migrant and 14 resident Egyptian Vultures Neophron percnopterus to analyse how environmental and social factors modulate overwintering immature population size, compare energetic consequences between migratory and resident individuals across wintering and non-wintering seasons and evaluate fitness components (i.e. survival and reproduction) between the two migratory forms. We observed that social attraction may influence the number of overwintering immature individuals, which increased linearly with adult birds surveyed. Residents spent more energy but exhibited higher survival probabilities and lower breeding activity. On the contrary, migratory birds showed lower energy expenditure during winter but also lower survival and more breeding attempts. These results suggest that social attraction may modulate population dynamics and promote residency in immature birds. Resident individuals benefit from enhancing their survival at the expense of higher energy expenditure during winter. Migrant birds, on the contrary, may compensate for the higher costs in terms of survival by a reduction in the energy cost, which may benefit more frequent breeding. Our results offer new insights to understand how species benefit from one strategy or another and that the coexistence of both migratory forms is context-dependent.

Significance statement

Animal populations exhibiting partial migration are composed of migrant and resident individuals who share the same breeding areas but different overwintering quarters. Deciphering the causes and consequences that affect each migratory behaviour is essential to understand the balance and persistence of the two strategies. Here, we investigate the environmental and social factors affecting number of immatures during winter and evaluate both migratory strategies in terms of energy expenditure, reproduction and survival. We found that social attraction modulates wintering population size of immature individuals and that the residency is energetically more costly but beneficial in terms of survival but not for breeding. By contrast, migration lessens the energy costs, increases the breeding activity, but also reduces survival probability.

中文翻译：

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环境和社会相关性，以及健康最大化对长寿清道夫不同迁徙行为的能量影响

摘要

部分迁移是分类群中最普遍的迁移策略之一。调查环境/社会因素之间的权衡——健康和精力充沛的后果——对于理解迁徙和居民行为的共存至关重要。在这里，我们编制了 25 只迁徙和 14 只常驻埃及秃鹫Neophron percnopterus越冬种群规模的现场监测数据和遥测数据分析环境和社会因素如何调节越冬的未成熟种群规模，比较越冬和非越冬季节迁徙和常驻个体之间的能量影响，并评估两种迁徙形式之间的健康成分（即生存和繁殖）。我们观察到社会吸引力可能会影响越冬未成熟个体的数量，该数量随着所调查的成年鸟类线性增加。居民花费更多的能量，但表现出更高的生存概率和较低的繁殖活动。相反，候鸟在冬季表现出较低的能量消耗，但也较低的存活率和更多的繁殖尝试。这些结果表明，社会吸引力可能会调节种群动态并促进未成熟鸟类的居住。居民个人受益于以冬季更高的能量消耗为代价来提高他们的生存率。相反，候鸟可以通过降低能源成本来补偿较高的生存成本，这可能有利于更频繁的繁殖。我们的结果提供了新的见解，以了解物种如何从一种策略或另一种策略中受益，并且两种迁徙形式的共存取决于环境。

意义陈述

表现出部分迁移的动物种群由迁移和常住个体组成，它们共享相同的繁殖区但不同的越冬区。解读影响每种迁徙行为的原因和后果对于理解这两种策略的平衡和持久性至关重要。在这里，我们调查了影响冬季未成熟动物数量的环境和社会因素，并从能量消耗、繁殖和生存方面评估了这两种迁徙策略。我们发现，社会吸引力会调节未成熟个体的越冬种群规模，并且居住在能量上更昂贵，但在生存方面有益，但对繁殖没有好处。相比之下，迁移降低了能源成本，增加了繁殖活动，但也降低了生存概率。