Results of the first taggings of Great Black-backed Gulls Larus marinus born in Gipuzkoa

Colonisation processes play a key role in demography by catalysing essential aspects of the geographical distribution, structuring and conservation of populations and species. In 2021, the first two Great Black-backed Gull Larus marinus chicks were ringed in Gipuzkoa, the province in which this gull had successfully reproduced for the first time in 2020. This note describes the recorded movements of these individuals up to 2024. One of the specimens was only resighted once when still at the nest. The other has been sighted 22 times, most recently on 15/12/2024 (+1264 days after ringing). These observations are concentrated in a small number of sites in certain Basque estuaries, all in the province of Gipuzkoa, at a maximum distance of 24 km from the ringing site. Despite being data from just a single bird, these results suggest a sedentary strategy with little apparent dispersion. This contrasts with the dispersion observed in juveniles from more northern populations whose mainly first-winter birds (sub-adult individuals that have not yet reached one year of age) disperse several hundred kilometres and reach the Cantabrian coast from their breeding sites in France, Ireland and the United Kingdom.