Sometimes parents must entice young from the nest with fish, but once fledged, chicks are on their own. The average breeding success ranges from 0.48 to 1.6 young per pair with losses due to predation, bad weather, and flooding from high tides. Behavior Black guillemots form monogamous pairs and show remarkable site fidelity, returning to the same colonies and often the same nest site year after year. Their social behavior ranges anywhere from solitary pairs to highly colonial. In the southern portion of their range guillemots are less social and less colonial, living in colonies of 10's and 100's while birds of the high arctic occur in colonies as large as several thousand.
Black guillemots show a variety of social behaviors towards each other.
They are territorial over nest sites, perching sites on stones and strongly defend perching sites above nests. Habitat Generally Black guillemots are restricted to rocky shores due to their nesting requirements. They nest most often in crevices among stones and boulders at the base of cliffs or cracks in cliffs, and less often under rocks among vegetation and under driftwood. In the high arctic some cliff sites may be as high as 230m. Foraging habitat varies dramatically with the seasons.