Alcidae

This family includes murres, guillemots, auklets, puffins, and murrelets, totaling 25 extant or recently extinct species across 11 genera, primarily found in the Northern Hemisphere.

Except for the extinct great auk, all auks can fly and are excellent swimmers, but they walk clumsily. While they resemble penguins in their black-and-white coloration and upright posture, they are not closely related and display examples of convergent evolution. Auks are generally monomorphic, with males and females appearing similar.

Auks are pelagic, spending most of their lives at sea and returning to land only for breeding. They are monogamous and form lifelong pairs, typically laying a single egg and reusing nesting sites annually. Nesting habits differ among species, with some forming colonies on cliffs and others, like puffins and auklets, nesting in burrows. All species except the Brachyramphus murrelets are colonial.