Isotopic (δ15N and δ13C) evidence for intersexual foraging differences and temporal variation in habitat use in waved albatrosses

Waved albatrosses ( Phoebastria irrorata Salvin, 1883) forage close to their breeding grounds on Isla Española, Galápagos, during the short chick-brooding stage and make long trips to the Peruvian upwelling during incubation and chick rearing. Previous studies have suggested foraging segregation by sex: females spend more time searching than males do while foraging in the Galápagos Marine Reserve (GMR), and band recoveries suggest higher bycatch vulnerability of males in the Peruvian upwelling. We used stable isotope analysis (δ15N and δ13C) of whole blood of adult male and female albatrosses to test for intraspecific foraging segregation in this sexually dimorphic species. Analysis of serial blood samples revealed higher δ15N values in males, suggesting consumption of prey items of higher trophic level. We also detected seasonal variation in foraging ecology, with higher δ15N values at the beginning of the breeding season. Sex and regional differences in δ13C values were not significant, reflecting primarily pelagic foraging sites of both sexes, both in the GMR and the Peruvian upwelling. Our results provide evidence of trophic segregation, suggestive of competitive exclusion, and novel information on marine isoscape values in the Eastern Equatorial Pacific.

Absence of Population Genetic Structure Among Breeding Colonies of the Waved Albatross

We used four variable microsatellite loci to examine the distribution of genetic variation and degree of genetic structuring among three subcolonies of Waved Albatrosses (Phoebastria irrorata). The breeding population of this species is almost entirely limited to the island of Española in the Galápagos Archipelago. Such strong philopatry could lead to population genetic structure among subcolonies on the island. Pairwise values of the FST analog, θ, calculated from microsatellite genotypes, were all less than 0.012, indicating little genetic differentiation and the presence of gene flow throughout the population.

Mate Opportunity Hypothesis and Extrapair Paternity in Waved Albatrosses (Phoebastria Irrorata)

Early arrival at breeding sites can influence reproductive success through enhanced access to critical resources such as nest sites or mates. One hypothesis explaining protandry, or male-first arrival at breeding sites, proposes that males arrive earlier to increase their extrapair copulation (EPC) opportunities, which may, in turn, enhance males' reproductive success through extrapair fertilizations (EPFs) (“mate opportunity hypothesis”). Extrapair behavior is unexpected in long-lived birds, in which the male is expected to abandon a brood of uncertain paternity, because his probability of future reproduction is high. A previous study of the Waved Albatross (Phoebastria irrorata), a long-lived, socially monogamous seabird, showed evidence of EPFs in 4 of 16 (25%) families. Here, we combined behavioral observations of copulations with additional molecular genetic evidence of EPFs in Waved Albatross families to investigate the fitness consequences of protandry under the mate opportunity hypothesis. During three breeding seasons, we documented 3,661 attempted copulations between birds of known identity; >60% of copulations that involved at least one breeding bird were classified as EPCs. Protandry was pronounced in all three study years: 76.3–96.6% of males arrived before (typically, 6–10 days before) their social mates. Early arrival was associated with increased opportunities for copulations: individual EPC frequencies were higher for breeding males than for breeding females, and males that arrived earlier than their social mates engaged in the most EPCs. Extrapair fertilizations were also regular in our study population; social fathers were excluded as the genetic sire in 14–21% of families. Egg laying dates of EPFs tended to be earlier in the season than those of within-pair fertilizations (WPFs). However, earlier arrival by a male did not translate into a higher probability of siring either within-pair or extrapair offspring, nor did cuckolding males have enhanced reproductive success. Although the fitness consequences of early arrival remain unclear, these findings suggest alternative advantages of early arrival for male Waved Albatrosses. La Hipótesis de Oportunidad de Apareamiento y Paternidad Extra-pareja en Phoebastria irrorata