Last evening, waves of starlings passed over our yard in Columbia, Missouri, moving toward a roost site somewhere northwest of our neighborhood. Though not native to North America, these maligned immigrants are among the most numerous and widespread of our avian species and are infamous for their massive communal roosts.
Most blackbird species, including grackles, red-winged blackbirds and starlings, utilize communal roosts, as do pigeons, robins, swallows, many wading birds, vultures and some waterfowl. The reasons for this behavior remain uncertain though most ornithologists believe it diminishes the risk of predation and improves foraging success; indeed, birds that forage in large flocks are more likely to roost in colonies than are those that feed alone or in small groups. While heat conservation has been suggested as a possible benefit of communal roosting, the above birding groups retain this behavior in warm southern latitudes.
Some birds that use communal roosts also nest in colonies (e.g. waders, swallows) but most abandon the practice during the breeding season, when territorial instincts take control. By late summer, as winter flocks reform, communal roost sites are established once again, not to be abandoned until the lengthening days of spring (or until angry humans, tired of the noise, smell and droppings, intervene).
