Migratory flyways and connectivity of Brown Headed Gulls (Chroicocephalus brunnicephalus) revealed by GPS tracking

Brown-Headed Gull ( Chroicocephalus brunnicephalus ) is the most common summer visitor gull on the Qinghai-Tibet Plateau (QTP) and is a species that is susceptible to highly pathogenic avian influenza (HPAI), however, their detailed migratory movements remain unclear. In this study, we applied GPS/GSM transmitters to track the journeys of individuals (n = 32) that bred at the Qinghai Lake in Qinghai province, China. The results showed that the Brown-Headed Gulls (n = 15 bird-years) from the same breeding population employed different flyways during southbound migration: western (n = 4 bird-years), central (n = 4 bird-years), and eastern (n = 7 bird-years), which indicates rather weak migratory connectivity for the breeding population (the mean distance between two individuals during winter was 1,040 ± 548 km (range = 81-2,002 km), spanning 35% of the maximum width of the QTP). Before the southbound migration, western migrants arrived at lakes (454 ± 319 km) farther from their breeding ground compared to central and eastern migrants to engage in nearly three months of post-breeding movement. Western migrants employed more detours and migrated longer distances crossing mountains with higher elevations (4,535 ± 105 m) during southbound migration. In contrast, central and eastern migrants employed more direct routes and migrated shorter distances crossing relatively lower-altitude mountains during their southbound migration. The western and central migrants undertook a distinct counterclockwise loop migration pattern shifting from the central QTP route in southbound migration to the eastern QTP route in northbound migration. They performed similar behaviors of duration and distance during the southbound and northbound migration. Our study can be considered as a baseline for the migratory patterns of potentially infected waterfowl on the Qinghai-Tibet Plateau, and it offers valuable insights into the migration movements of gulls in the region.