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Age at First Return and Breeding of Razorbills (Alca torda) on the Gannet Islands, Labrador and Machias Seal Island, New Brunswick

Abstract Resightings of Razorbills (Alca torda) banded as chicks on the Gannet Islands, Labrador (N = 1,873 resightings of 638 individuals) and Machias Seal Island, New Brunswick (N = 870 resightings of 291 individuals) were used to estimate the timing and age at first return to the natal colony and age at first breeding. In total, 14 one-year-old and 110 two-year-old birds were observed on land. All one- and two-year-old birds were seen for the first time on the islands late in the breeding season after laying had occurred, with two-year-olds returning to the colony on average three weeks earlier than one-year-old birds. Age at first breeding was significantly lower on Machias Seal Island than the Gannet Islands, 3.88 ± 0.13 SE and 4.40 ± 0.13 SE years, respectively (range two to six years, N = 123). Four two-year-old birds were observed engaging in courtship and breeding behaviors, including copulation. Overall, age at first return and breeding was lower than for known European Razorbill colonies and is likely due to low breeding densities and fidelity at the two North American colonies studied.