History, dispersal and habitat selection in Central European Caspian gulls Larus cachinnans: a study of birds originating from a single breeding colony

The Caspian gull (Larus cachinnans) has recently spread from Ukraine (northern coast of the Black Sea, River Dnipro) to Poland, Germany and other European countries. The first breeding birds in the Czech Republic were recorded in 1990 at the Nove Mlýny Reservoir (NMR), since when the number of breeding pairs has increased to 248 (2020). As there is little available information on the dispersal and spread of Caspian gulls from Central European breeding populations, pulli Caspian gulls hatched at the NMR were tagged to reveal dispersal patterns and habitat selection. By combining the recovery of ringed birds and data from telemetry loggers, we found that gulls from the NMR dispersed in all directions, with the main destinations being within the Czech Republic, Poland, Germany, the Netherlands, Belgium and Hungary; however, dispersal intensity and distance travelled differed depending on the direction taken, with the farthest dispersal distance being 1714 km to Spain. Telemetry recordings indicated waterbodies (including water courses, seas and oceans) as the most selected environment, followed by landfill sites, mineral extraction sites, industrial or commercial units (including roofs of buildings) and arable or other agricultural land. Extensive aquacultural fish ponds, open landfill sites or large areas of managed arable land all represent important food sources and are likely to be key factors enabling the spread of Caspian gulls within the Czech Republic and elsewhere around Central Europe.