The Breeding Ecology of Homed Puffins Fratercula comiculata in Alaska.

Abstract

The Horned Puffin {Fratercula corniculata) is one of three North Pacific puffin species. Horned Puffins almost always nest amongst boulders and in rock crevices. This makes access to nest-sites and chicks difficult and, as a result, sample sizes are small for many their breeding parameters. I studied the breeding ecology of Homed Puffins at Duck Island, Alaska, over a period of five years (1995-1999) in order to improve our baseline knowledge of this species and the variability in its breeding ecology. Adults fed their chicks primarily on sandlance {Ammodytes hexapterus), which comprised over 90% of the diet. Chick survival to fledging was generally high (83-97%), and there was no apparent difference among years in breeding success, despite evidence of poor food availability in 1998. There was, however, a large range of chick growth rates and fledging ages. Chick mass growth rate was lowest in 1998, and chicks also fledged at youngest ages in that year. The impacts of reduced food supply on growth differed between different body components, suggesting differential allocation of energy and nutrients into the growth of different body structures. There was no difference among years in either chick diet or the mass of food loads bought to the colony by adults. Daily counts of Homed Puffins attending the colony were made throughout the breeding season in three consecutive years in order to examine the diurnal, seasonal and annual variation in colony attendance, and the implications of this variation for population monitoring. Peak diurnal attendance occurred between 2030-2130. Despite high seasonal and annual variation in colony attendance, overall mean numbers of birds present at the colony during both incubation and chick-rearing did not differ among years. There was greater variability in attendance during chick- rearing than during incubation, indicating that counts conducted during incubation may provide the better index of breeding population size. [brace not closed]