Uria aalge

Nonbreeding: pelagic and along rocky seacoasts (AOU 1983). Nests in the open or in crevices on broad and narrow cliff ledges, on stack (cliff) tops, and on flat, rocky, low-lying islands; less commonly nests under boulders or in caves; usually nests in same exact site in successive years (Harris and Birkhead 1985). Cliff-top nests in Washington had lower reproductive success than did crevice nests in vertical cliffs (Parrish 1995, Auk 112:390-401).

In Newfoundland, median potential foraging range (from breeding colony) was 37.8 km for incubating birds, 5.4 km for chick-rearing birds (Cairns et al. 1987). However, in northwestern Alaska, telemetry data from incubating or chick-rearing birds indicated that they regularly foraged up to 100 km from their colonies (Hatch et al. 2000). Annual adult survivorship greater than 85%. Up to 3900/sq km reported in winter on Grand Banks off Newfoundland. In California, Western Gull sometimes is an important predator on eggs and chicks (Spear 1993). High density breeding may reduce vulnerability to predators (J. Anim. Ecol. 60:721).

Laying peaks in second half of June in southeastern Canada and in mid-June in western Gulf of Alaska. Mean laying date on the Farallon Islands, California, varies among years from early to late May (Sydeman and Eddy 1995, Condor 97:1048-1052). Both sexes, in turn, incubate 1 egg for 32-34 days (also reported as 28-35 days). May produce one or more replacement eggs if egg is lost during incubation. Young are fed at nest 18-25 days (also reported as 16-32 days) (average varies from about 19 to 23, affected by laying date, among other factors), then go to sea, tended by adult male for a few weeks. First breeds at about 3-5+ years. Breeding colonies may be large, with exceptionally high density; colony on Castle Rocks, California, had about 126,000 breeding birds in early 1980s (Spendelow and Patton 1988).