quality:correction, structural:summarization, stylistic:tone, structural:expansion
Breeding and colonies

Auks are pelagic birds, spending the majority of their adult lives on the open sea and going ashore only for breeding, although some species, such as the common guillemot, spend a great part of the year defending their nesting spot from others.

Auks are monogamous, and tend to form lifelong pairs. They typically lay a single egg, and they use the nesting site year after year.

Some species, such as the Uria guillemots (murres), nest in large colonies on cliff edges; others, such as the Cepphus guillemots, breed in small groups on rocky coasts; and the puffins, auklets, and some murrelets nest in burrows. All species except the Brachyramphus murrelets are colonial.