Lensink R (2016) Gull roosts on roof-tops. LIMOSA 89 (4): 163-169.

Night roosts of gulls around the city of Eindhoven (SE Netherlands) were studied to describe the number of nonbreeding gulls in this region, the location of roosting sites and the behaviour of gulls on roosts. Black-headed Gull Chroicocephalus ridibundus was the most numerous gull species. In the afternoon most gulls arrived around sunset and they left before sunrise in the morning. In winter Blackheaded Gulls arrived later relative to sunset than in spring. Gulls roosted on an artificial lake and on roof-tops of buildings in an industrial area 4 km away. In the first hours after sunset gulls often switched from the lake to roof-tops; these two roost sites seemed to function in tandem. Therefore, we called it a ‘tandem-roost’. In the dark, movements from the lake to the roof were preceded by synchronised swimming in the direction in which the birds later left. We also located gull roosts in surrounding regions and found three other tandem-roosts, all consisting of a water site and a roof-top site. Elsewhere in the Netherlands, more roosts on roof-tops were found as well. This suggests that the use of roof-tops seems to be more common than previously thought. Even in the Dutch river deltas, with many large waterbodies, gulls roost on roofs in industrial areas and harbours, which suggests that roofs have advantages to open water. They may be just as safe against ground predators like Red Fox, but are free of waves and currents, which may cost energy for a roosting gull to remain in place. As far as we know roof-tops used as roosts are always situated near open water used for drinking, bathing and preening.

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