Black-headed Gulls (Chroicocephalus ridibundus) don't just return to the same roost site every night, but also to specific daytime sites like a park or a river stretch, often over multiple years. They appear to specialise in familiar foraging habitats in winter
#Switzerland #Biodiversity #Basel

In our 2021 national roost count, we recorded 39,000 individuals, more than the 32,000 counted in the regular waterbird census. This means Switzerland hosts around 1.5% of the Western European winter population of this species

#Ornithology #CitizenScience #Gulls

10+ Years of Black-headed Gull Research: Ring-reading in a youth birding group evolved into Switzerland’s first nationwide, coordinated roost count, involving many volunteers

Both studies are now published in the Ornithologischer Beobachter, available here: www.researchgate.net/profile/Vale...
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Further, while observing Black-headed Gull at roosts before and after the count, we counted even higher numbers of birds during spring migration. My hypothesis: These #gulls rest in lake-rich Switzerland (here: #Zurich) a final time before migrating back to the breeding colonies in NE-Europe 🌍

New #research! Trying to find the true winter abundance of #Black-headedGulls in Switzerland, we organised a national count - at the overnight roosts! With this method, we recorded with 39'000 gulls about 20 % more than during the traditional (diurnal) water bird counts