An estimate of the population sizes of Black-browed (Thalassarche melanophrys) and Grey-headed (T. chrysostoma) Albatrosses breeding in the Diego Ramírez Archipelago, Chile

The Diego Ramirez Archipelago, Chile, is the southernmost albatross breeding ground in the world and holds globally important numbers of Black-browed (Thalassarche melanophrys) and Grey-headed (T. chrysostoma) Albatrosses. A census in the Diego Ramirez Archipelago has been attempted only once, in 1980–81, with methods that were unlikely to determine population sizes accurately. The number of breeding pairs of both species was estimated in the incubation period of 2002 using a combination of aerial photography, ground-based photography, yacht-based photography and ground counts. All islands in the archipelago were surveyed. There were an estimated 55 000 pairs of Black-browed and 17 000 pairs of Grey-headed Albatrosses breeding at the archipelago. Based on the results of this census, and those for the other four known breeding locations, the populations of both species of albatrosses in Chile are considerably larger than previously reported, comprising ~20% of the Black-browed Albatrosses and 23% of Grey-headed Albatrosses in the world, with the largest populations of both species occurring in the Diego Ramirez Archipelago.