Post‐fledging migration and wintering strategies of individual juvenile Lesser Black‐backed Gulls (Larus fuscus)
Research into the patterns and drivers of juvenile migration is important for understanding the development of individual migration strategies. Although several recent studies have tracked adult large gulls throughout the annual cycle, the movements of juveniles remain poorly understood. We fitted Global Positioning System (GPS) devices that transmit locations through the Global System for Mobile Communications (GSM) to ten juvenile Lesser Black‐backed Gulls Larus fuscus prior to fledging on the island of Spiekeroog, Germany, to study their first autumn migration and wintering behaviour. The tracked birds initially departed on similar compass bearings south to southwest, after which migration routes diverged. Individuals took 38–107 days to reach their wintering sites in Algeria, Morocco or Spain. Birds visited 6.7 ± 3.7 (mean ± sd) stopover sites en route and spent substantial time in northern Europe, with some individuals converging at the same sites over small spatial scales (< 1km), but not over the same time periods. Birds increased travel speeds in the second half of their migration. They showed relatively high site-fidelity after arrival at wintering sites, and there was no evidence that the size of foraging areas increased over time, suggesting limited exploratory behaviour. Individuals used the same predominant habitats – cropland, open water and built-up areas – to varying degrees, but showed limited variation in habitat use over time. Overall, the migration routes and timings of juveniles broadly resembled those of previously tracked adults. Given their similar initial bearings and abundance of large gulls on the flyway, we suggest that social learning is likely to be an important process shaping the individual migration and wintering strategies of juvenile gulls.
Authors: Borrmann, Rahel M., Phillips, Richard A., Clay, Thomas A., Garthe, Stefan