FEMALE-BIASED SEX RATIO ARISES AFTER PARENTAL CARE IN THE SEXUALLY DIMORPHIC WAVED ALBATROSS (PHOEBASTRIA IRRORATA)

Abstract

Abstract In response to evidence of sexual segregation at foraging grounds as well as male-biased band recoveries, we investigated the ontogeny of the female- biased adult sex ratio in the Waved Albatross (Phoebastria irrorata), an IUCN “critically endangered species” essentially endemic to Isla Espanola, Galapagos, Ecuador. Using a molecular technique to determine the sex of chicks and adults and known fate analysis of chicks during rearing, we found no evidence of a sex-ratio bias at hatching or fledging in three consecutive years with variable reproductive success. Although male chicks were significantly larger than females at fledging, survival to fledging of a large sample of male and female chicks did not differ. The sex ratio among a cohort of young adults at approximately the age of first breeding (eight years) also did not differ significantly from parity. Differential adult mortality, including male-biased mortality in fisheries, is the most probable cause of a female- biased population sex rati...