Introduction

This tiny alcid is one of the most abundant seabirds in North America, with a total population of about nine million. Least Auklets dive for plankton, nest in huge colonies in rock crevices, lay just one egg each year, and eat almost 90% of their weight per day—reflecting the high energetic demands of their flight and foraging. This species breeds on the Aleutian Islands and on remote islands in the Bering Sea, and winters at sea near breeding sites as far north as open water permits.

Like the Dovekie (Alle alle), the Least Auklet’s ecological counterpart in the North Atlantic, calanoid copepods are the preferred prey. During the breeding season, both sexes possess three kinds of facial ornaments: a colorful bill, a horny bill-knob ornament, and white facial plumes. Adult summer plumage varies from white through spotted intermediates to nearly black on the breast, and plumage color functions as a status signal. This is a socially monogamous species and mate choice is mutual, but there is relatively low mate fidelity between breeding seasons. Sperm competition may be an important aspect of the breeding system—males have by far the largest testis size relative to body size of any alcid. This species has a low survival rate relative to other alcids, with a predicted average life expectancy of about 4.5 years. Rats and foxes threaten some colonies.