The Crested Auklet is a small, odd-looking seabird that breeds in colonies on remote islands and coastlines around the Bering Sea and winters in flocks on nearby waters. Its conspicuous crest ornament is present in both sexes and varies in size both within and between age groups. Crested Auklets are socially monogamous; both sexes prefer mates with large crests, an example confirming Darwin's theory of mutual sexual selection. Males, and to a lesser extent females, compete aggressively for mates and nest sites, and crest size correlates with dominance. Pairs engage in elaborate courtship behavior with stereotyped postural displays that increase in intensity as courtship proceeds; displays may attract other Crested Auklets in jostling melees. Both sexes have a distinctive, pungent, citrus-like odor to their plumage, a trait this species shares with the closely-related Whiskered Auklet (Aethia pygmaea).
Breeding colonies are located on sea-facing talus slopes, cliffs, boulder fields, and lava flows, all of which provide abundant rock crevices suitable for nesting. As part of the daily activity of this auklet, or triggered by predators or disturbance, huge flocks sometimes circle between sea and breeding colony, often rising more than 500 m above sea or colony, a spectacular sight. Colonies with over 100,000 pairs have been described, although variable attendance and inaccessible nests located deep in crevices make auklets difficult to census.
This auklet dives for its food, primarily euphasiids, and lays but a single egg per clutch. Both male and female help to care for their semi-precocial young, which fledges at almost adult size after about 33 days in its nesting crevice.