Year-round spatial movements and trophic ecology of Trindade Petrels (Pterodroma arminjoniana)

Abstract

Trindade Petrels (Pterodroma arminjoniana) are vulnerable gadfly petrels that breed on the remote Trindade Island, located ~1100 km off the Brazilian coast. Little is known about their spatial ecology, and their trophic ecology has only been described for the breeding season. We tagged four Trindade Petrels with global location sensing loggers (GLS) from October 2013 to November 2014 and sampled the blood and feathers (innermost primary and the eighth secondary) of 14 individuals to evaluate their year-round spatial and isotopic ecology. We examined individual distributions, habitat use and suitability, activity, and isotopic values during the breeding, migration, and non-breeding periods. Trindade Petrels used areas in the southwest Atlantic Ocean (between 10°N and 50°S in latitude) during the breeding season. They migrated through pelagic waters of the tropical Atlantic to the northwest Atlantic, where they spent the non-breeding season. Trindade Petrels used mostly tropical to subtropical waters in areas of intermediate to high wind speeds and low marine productivity. Individuals spent more time foraging at night than during the day. During the breeding season, birds in northerly areas had higher carbon-13 values, and birds that used more pelagic areas foraged on prey at a higher trophic level (higher nitrogen-15 values) than those in more southern and coastal areas. Isotopic values during the breeding, migration, and non-breeding periods differed, possibly due to differences among individuals in their at-sea distribution throughout the year. We confirmed the non-breeding distribution of Trindade Petrels, which was previously known only from vessel sightings and stranded birds. Our results also suggest a strong temporal segregation in the at-sea distribution and trophic ecology between two groups of individuals, which might indicate the existence of two separate breeding populations.