Data from: Terrestrial and marine foraging strategies of an opportunistic seabird species breeding in the Wadden Sea

Lesser black-backed gulls Larus fuscus are considered to be mainly pelagic. We assessed the importance of different landscape elements (open sea, tidal flats and inland) by comparing marine and terrestrial foraging behaviours in lesser black-backed gulls breeding along the coast of the southern North Sea. We attached GPS data loggers to eight incubating birds and collected information on diet and habitat use. The loggers recorded data for 10–19 days to allow flight-path reconstruction. Lesser black-backed gulls foraged in both offshore and inland areas, but rarely on tidal flats. Targets and directions were similar among all eight individuals. Foraging trips (n = 108) lasted 0.5–26.4 h (mean 8.7 h), and ranges varied from 3.0–79.9 km (mean 30.9 km). The total distance travelled per foraging trip ranged from 7.5–333.6 km (mean 97.9 km). Trips out to sea were significantly more variable in all parameters than inland trips. Presence in inland areas was closely associated with daylight, whereas trips to sea occurred at day and night, but mostly at night. The most common items in pellets were grass (48%), insects (38%), fish (28%), litter (26%) and earthworms (20%). There was a significant relationship between the carbon and nitrogen isotope signals in blood and the proportional time each individual spent foraging at sea/land. On land, gulls preferentially foraged on bare ground, with significantly higher use of potato fields and significantly less use of grassland. The flight patterns of lesser black-backed gulls at sea overlapped with fishing-vessel distribution, including small beam trawlers fishing for shrimps in coastal waters close to the colony and large beam-trawlers fishing for flatfish at greater distances. Our data show that individuals made intensive use of the anthropogenic landscape and seascape, indicating that lesser black-backed gulls are not a predominantly marine species during the incubation period.

小黑背鸥（Lesser black-backed gulls，学名Larus fuscus）被认为主要为远洋性（pelagic）物种。本研究通过比较北海南岸沿岸繁殖的小黑背鸥的海洋与陆地觅食行为，评估了外海、潮间带滩涂与内陆生境等不同景观要素的重要性。研究人员为8只处于孵卵期的个体佩戴了GPS数据记录仪（GPS data loggers），并收集了其食性与生境利用相关信息；记录仪连续记录10至19天，以支持飞行路径的重建。小黑背鸥的觅食区域涵盖远海与内陆，但极少利用潮间带滩涂。8只受试个体的觅食目标与方向均较为一致。本次研究共记录到108次觅食行程，单次觅食时长为0.5至26.4小时（平均8.7小时），活动范围为3.0至79.9千米（平均30.9千米），单次觅食总行程为7.5至333.6千米（平均97.9千米）。远洋觅食行程的各项参数均较内陆觅食行程具有更显著的变异性。个体在内陆生境的活动与日照时长紧密相关，而远洋觅食行程可发生于昼夜，但多集中于夜间。受试个体的反刍食团（pellets）中最常见的成分为禾草（48%）、昆虫（38%）、鱼类（28%）、垃圾（26%）与蚯蚓（20%）。血液中的碳、氮同位素信号与个体在海洋/陆地觅食的时长占比存在显著相关性。在陆地觅食时，小黑背鸥优先选择裸地，显著更多地利用马铃薯田，而较少利用草地。其远洋飞行路径与渔船分布高度重叠，包括在繁殖地近岸水域捕捞虾类的小型桁拖网渔船（beam trawler），以及在更远海域捕捞比目鱼的大型桁拖网渔船（beam trawler）。本研究数据表明，小黑背鸥会高强度利用人为改造的陆地与海洋景观，这说明在孵卵期，小黑背鸥并非严格意义上的远洋性物种。