Breeding biology of the Fork-tailed Storm-Petrel Oceanodroma furcata on Kasatochi Island, Aleutian Islands, Alaska

SUMMARY DRUMMOND, B.A. & LEONARD, M.L. 2009. Breeding biology of the Fork-tailed Storm-Petrel Oceanodroma furcata on Kasatochi Island, Aleutian Islands, Alaska. Marine Ornithology 37: 265–273. We present the first detailed account of breeding biology in Fork-tailed Storm-Petrels Oceanodroma furcata from the Aleutian Islands, Alaska, where nearly two thirds of the global breeding population occurs. We examined timing of breeding, breeding success, chick growth, parental provisioning and chick diet during two consecutive breeding seasons at a colony in the central Aleutians. Most adults laid eggs before late May, eggs hatched between mid-June and early August and chicks began fledging in mid-August. Timing of breeding varied between years, with an earlier mean hatch in 2005 than in 2006. Hatching success was consistently high in both years (89% in 2005, 91% in 2006), but fledging success varied substantially between years (58% in 2005, 89% in 2006), indicating that factors that influence chick survival may drive annual breeding success. Visitation rate, meal size and composition of chick diets also varied between years, suggesting that foraging conditions varied during our study. Food availability and weather conditions may both have contributed to the variation we observed in timing of breeding and fledging success.