Age-related spatial ecology of Audouin's gull during the non-breeding season

For vulnerable and endangered migratory species, an important and often overlooked aspect of conservation is their non-breeding distributions. For long-lived species, an additional constraint is the lack of data on juvenile movements. Individual relationships between age, movement ecology, and habitat preference for long-lived migratory birds remain understudied. According to the exploration-refinement hypothesis, adults should select better and more productive areas for foraging than inexperienced juveniles. Here, we explored the differences in migratory patterns, habitat selection, and foraging behaviour between juvenile and adult Audouin's gulls Ichthyaetus audouinii, a species listed as Vulnerable by the IUCN. We captured 4 juveniles and 6 adults in the San Pedro colony (SE Spain) and equipped them with high-resolution 5 min programmed GPS loggers to track their postnuptial or first migration and subsequent non-breeding destinations. Our findings show that juveniles tended to migrate longer distances than adults, that the time spent foraging between age groups did not differ, and that adults used a greater variety of habitats than juveniles and positively selected some foraging habitats, such as waterbodies. Age-related differences in migratory patterns and habitat exploitation during the non-breeding period can be explained by the avoidance of competition between juveniles and adults and the adults' greater experience in foraging performance. Our results bring important insights into the age-related differences in habitat exploitation of a Vulnerable seabird, which could help improve conservation strategies across its non-breeding range.