Effects of Age and Culling on Movements and Dispersal Rates of Yellow-Legged Gulls (Larus michahellis) from a Western Mediterranean Colony

Abstract

This study reports the effects of age and culling of breeding adults on movements and dispersal rates of Yellow-legged Gulls (Larus michahellis) from a western Mediterranean colony (the Medes Islands) based on recaptures and resightings of birds banded as chicks. Juveniles (1-year-old birds) were most frequently located in the French coast of Biscay and in the Western North Mediterranean. Older gulls became concentrated near the colony and its surroundings (core area), with 3rd year sub-adults and adults accounting for more than 70% and 90% of resightings in this area, respectively. Culling of breeding adults increased the dispersal rate of juveniles (pre-cull: 62.6% ± 6.0 SD; post-cull: 71.2% ± 6.4 SD) and mean distance of resightings of juveniles (pre-cull: 250.5 km ± 267.6 SD; post-cull: 367.6 km ± 300.1 SD), and favored displacement of juveniles to the French Atlantic coast. Culling also increased the dispersal rate of adults (pre-cull: 31.7% ± 16.6 SD; post-cull: 38.8% ± 16.3 SD) and mean distance of adult resightings (pre-cull: 27.4 km ± 108.7 SD; post-cull: 35.7 km ± 113.0 SD). This could be attributed to an increase in the number of gulls recruited to other colonies near the Medes Islands after culls. Culling performed in the Medes Islands colony seems to have effects at metapopulation level, conditioning the dynamics and management of other colonies.