Understanding the at-sea movements of wide-ranging seabird species throughout their annual cycle is essential for their conservation and management. Habitat use and resource partitioning of Laysan (Phoebastria immutabilis) and black-footed (Phoebastria nigripes) albatross are well-described during the breeding period but are less understood during the post-breeding period, which represents ~40% of their annual cycle. Resource partitioning may be reduced during post-breeding, when birds are not constrained to return to the nest site regularly and can disperse to reduce competitive pressure. We assessed the degree of spatial segregation in the post-breeding distributions of Laysan (n = 82) and black-footed albatrosses (n = 61) using geolocator tags between 2008 and 2012 from two large breeding colonies in the Northwestern Hawaiian Islands, Midway Atoll, and Tern Island. We characterized the species-and colony-specific foraging and focal distributions (represented by the 95 and 50th density contours, respectively) and quantified segregation in at-sea habitat use between species and colonies. Laysan and black-footed albatross showed consistent and significant at-sea segregation in focal areas across colonies, indicating that resource partitioning persists during post-breeding. Within breeding colonies, segregation of foraging areas between the two species was more evident for birds breeding at Tern Island. Spatial segregation decreased as the post-breeding season progressed, when spatial distributions of both species became more dispersed. In contrast to studies conducted on breeding Laysan and black-footed albatross, we found that sea surface temperature distinguished post-breeding habitats of black-footed albatrosses between colonies, with black-footed albatrosses from Midway Atoll occurring in cooler waters (3.6°C cooler on average). Our results reveal marked at-sea segregation between Laysan and black-footed albatross breeding at two colonies during a critical but understudied phase in their annual cycle. The observed variation in species-environment relationships underscores the importance of sampling multiple colonies and temporal periods to more thoroughly understand the spatial distributions of pelagic seabirds.

· We report resightings of individually-marked Two-banded Plovers (Charadrius falklandicus) breeding in northern Patagonia across two consecutive seasons in two beaches separated by approximately 65 km in a straight line: Playas Blancas (Península Valdés) and Playa Paraná (Puerto Madryn), Chubut province, Argentina. We captured and banded 24 adults at the nest while incubating during 2016. Nineteen banded individuals (ca. 80%) were resighted in 2017, 17 on the same site where they were banded, while 2 moved between survey sites. Only 32% were found breeding again while the remaining 68% were resighted resting or foraging, solitarily or in mixed flocks with other shorebird species. Among the resighted breeders, two adults were found paired with a different banded partner as in the previous year. The remaining breeders were paired with unbanded partners, and hence mate fidelity could not be assessed. Our findings add information to the scarce data on the breeding biology of this species suggesting that Two-banded Plovers exhibit site fidelity.Resumen · Avistamientos de Chorlos Doble Collar (Charadrius falklandicus) durante el período reproductivo en la costa de Chubut, Patagonia, Argentina Presentamos avistamientos de Chorlos Doble Collar (Charadrius falklandicus) anillados en dos playas de la provincia de Chubut, Argentina: Playas Blancas (Península Valdés) y Playa Paraná (Puerto Madryn) separadas entre si aproximadamente 65 km en línea recta. En la temporada 2016, se capturaron y anillaron 24 individuos adultos durante la incubación. La mayoría de ellos (19, ca. 80%) fueron avistados en la temporada 2017, 17 en el mismo sitio donde fueron anillados y 2 en el otro sitio de estudio. El 32% se observó anidando mientras que, el 68% restante, se observó en el área descansando o alimentándose en forma solitaria o en bandadas mixtas con otras especies de aves playeras. Entre los individuos reproductores en 2017, dos anidaron con parejas también anilladas aunque diferentes al año anterior. Los reproductores restantes se observaron con parejas no marcadas, por lo que no se pudo evaluar si estaban apareados con el mismo individuo que en la temporada anterior. Estos resultados aportan nuevos datos sobre la biología reproductiva de esta especie que se suman a los estudios previos en la zona, sugiriendo que los Chorlos Doble Collar muestran fidelidad al sitio reproductivo.