Caspian Gulls Larus cachinnans have expanded their breeding range over ~2500 km westward, from the Black Sea to Western Europe, within decades. As a colonising species it invaded a region with two established guild members that faced poor breeding results from declining resources. A study of breeding performance and diet of the Caspian Gulls, in combination with a tracking study to document foraging behaviour and habitat choice, meant 27 to examine the possible occurrence of interspecific competition. The study revealed a multi-dimensional ecological separation between taxa, resulting from differences in prey choice, spatial segregation in micro- and macro-habitats plus an essential difference in seasonal timing. Caspian gulls focused on freshwater habitats, ditches and canals in agricultural areas, while avoiding offshore marine and intertidal areas, and took different prey in major areas where other taxa co-occurred. On top of that, Caspian Gulls commenced breeding a month earlier than its two sympatric guild members, such that their energetic demands peaked (during chick rearing) well before that in the established taxa. Caspian Gulls, in their early days of colonisation, have not invaded occupied territory, but found an open niche.

The data file includes the following fields: device_info_serial (device ID, 1ID per individual bird) date_time (timestamp without time zone yyyy-mm-dd hh:mm:ss) latitude (decimal degrees) longitude (decimal degrees) altitude (m, above mean sea level) speed_2d (m/s, ground speed from GPS tracker) The data is stored in the UvA-BiTS central database and extracted from the start day of tracking until 2023/07/01 for the study period. Data was extracted on 2024/12/20.