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

Relationships between individuals age and the movement ecology and habitat preference of long-lived migratory birds still remain understudied. According to the exploration-refinement hypothesis it is thought that adults would select better and more productive areas for foraging than inexperienced juvenile birds would do. Additionally, age-related differences in migratory patterns and exploited habitats could be explained by the attempt to avoid competition between juveniles and adults. Here, we explored the differences in the migratory patterns, habitat selection and foraging behaviour between juvenile and adult Audouins gulls (Ichthyaetus audouinii), a species listed as vulnerable by the IUCN. We captured 9 juveniles and 8 adults in the colony of San Pedro (SE Spain) and equipped them with high-resolution 5-min programmed GPS to track their postnuptial/first migration and non-breeding destinations. First, juveniles tended to migrate longer distances than adults did. Second, the time spent foraging between age groups did not differ. Third, freshwater masses constituted an essential habitat during the non-breeding season for both juveniles and adults. Fourth, we found that adults used a greater variety of habitats than juveniles did, but adults positively select foraging habitats despite the low availability while juveniles do not. Finally, repeatability in habitat use of individuals of the same age was rather low. We provided evidence of age-related differences in migratory patterns and habitat exploitation during the non-breeding period in a migratory seabird which can be explained by the avoidance of competition between adults and juveniles and the greater experience in foraging performance that adults have in comparison with juveniles.