Short report on probable case of Caspian Gull predation on migrating swallows observed at first time

At Mietków Reservoir (SW Poland), during the breeding season of 2019, we found 52 dead swallows in Caspian Gull (Larus cachinnans) colony. Most of them were Barn Swallows (Hirundo rustica). The bodies of swallows were fresh and torn with traces of bill. We assume that swallows might have been in weak condition and hunted by gulls. They also could die because of bad weather conditions and hypothermia, fell into the water and then were taken. However, to our knowledge, it was the first mass event of feeding on migrating birds by Caspian Gull.