Age-dependent survival of island vs. mainland populations of two avian scavengers: delving into migration costs

摘要: Large terrestrial long-lived birds (including raptors) are typically sedentary on islands, even when they migratory the mainland. Density-dependent variation in age at first breeding has been described as responsible for long-term persistence of bird populations islands. However, island may also benefit from higher survival rates derived absence migration costs, especially young individuals. Thus, can mimic a natural experiment to study costs. We estimated age-dependent two raptors Menorca (Egyptian vultures Neophron percnopterus and red kites Milvus milvus) compared these estimates with those reported other populations. In Menorca, Egyptian vultures, but not kites, showed low levels human-related mortality resulting extremely high probabilities, probably due different diet choices behavioral patterns. Juvenile studied population had lower probabilities than adults. This difference, however, was smaller mainland migrant populations, which juvenile rate. fact, between-population comparisons suggested that be triggered by factors wintering areas. contrast, adult respond Our results suggest raptor species become islands pre-breeder prospects comparison their counterparts. combination an earlier reproduction, facilitate persistence.