Breeding Thin-Billed Prions Use Marine Habitats Ranging from Inshore to Distant Antarctic Waters

SIMPLE SUMMARY: Thin-billed Prions are small seabirds with large foraging ranges. Thin-billed prions from the Falkland Islands were tracked with Global Positioning System (GPS) dataloggers during the breeding season. During incubation trips, Thin-billed Prions travelled distances of approx. 2000 km, and foraged on the Patagonian Shelf or in Polar Front waters. During chick-rearing, Thin-billed Prions undertook trips of variable duration (one to 11 days), and foraged more locally, including in inshore waters. Birds from two colonies used spatially segregated foraging areas. ABSTRACT: Pelagic seabirds cover large distances efficiently and thus may reach a variety of marine habitats during breeding. Previous studies using stable isotope data and geolocators suggested that Thin-billed Prions breeding in the Falkland Islands in the Southwest Atlantic may forage in temperate waters over the Patagonian Shelf or cross the Drake Passage to forage in Antarctic waters south of the Polar Front. We deployed miniature GPS dataloggers to track Thin-billed prions in the Falkland Islands during incubation (3 seasons) and chick-rearing (2 seasons). Thin-billed Prions had a wide distribution during incubation, covering latitudes between 43 and 60° S, with trip lengths of ca. 2000 km over seven days, on average. Thin-billed Prions from two nearby sites (60 km apart) were spatially segregated in their incubation trips, with New Island Thin-billed Prions foraging over the Patagonian Shelf, compared to Thin-billed Prions from Bird Island, that foraged in the region of the Polar Front. During chick-rearing, Thin-billed Prions from New Island undertook both long trips to the Patagonian Shelf and south of the Polar Front (30% of trips were 5–11 days), and short trips (70% of trips were 1–4 days) when they foraged more locally, including in inshore waters around the Falkland Islands. Females carried out more trips to distant sites. Thus, Thin-billed showed a high flexibility in foraging areas, habitats and foraging trip durations, which enable them to benefit from both, temperate and Antarctic environments.