Why do crows congregate in large numbers to sleep?
One of the great animal phenomena of the world is the congregation of large numbers of birds into a single group to sleep together. Such communal sleeping groups are known as “roosts.” Many species roost in groups; such things as crows, robins, starlings, blackbirds, swallows, and herons. Most do this only outside of the breeding season. Some species, like starlings, also forage together in great numbers. Others, such as herons, disperse out from these gathering areas to forage singly. For crows, roosts are primarily a fall and winter thing. Numbers peak in winter and then decrease near the beginning of the breeding season (usually in March). It appears that all crows will join winter roosts, even territorial breeding crows. Most breeding crows sleep on their territories during the breeding season, but join the roosts afterward. For an interesting account of a large urban roost in central New York (pictured above), check out the website dedicated to the roost in Auburn, NY
