Scientific name: Corvus brachyrhynchos
Common name: American Crow
(This information was compiled by Aaron Serene for Biology 220W in Spring 2000 at Penn State New Kensington)
The American crow is an obvious (and often loud!) avian species that inhabits a variety of habitat areas in and around the Penn State New Kensington Nature Trail. The American crow is a large (17 to 21 inches long with a wing span up to three feet), chunky, black bird that is found in the form of a variety of interbreeding sub-species all across North America.
Crows are seldom seen alone. In the non-breeding part of the year (fall through the winter) they form large, communal flocks of hundreds to thousands of individuals. Smaller sub-groups of these communal flocks daily forage out across the countryside sometimes traveling as far as thirty miles from a central roosting area. During the breeding season (spring to late summer) the crows form smaller, familial flocks but still forage in small groups daily searching for food. The flocks, especially the very large non-breeding flocks, establish distinct "pre-roosting areas" within which they engage in a variety of energetic vocal and flight communication behaviors (often to the dismay of humans in the immediate area!) before retiring to their true "roosting areas". Communication between individuals in the foraging groups and within the larger roosting flocks is a very important aspect of crow biology. The remarkable and extensively documented intelligence of crows (their ability to solve food-gathering problems, to learn to mimic human vocalizations, to employ a variety of complex strategies to gather food etc) is thought to be a direct extension of their evolutionary success as a social, highly efficiently communicating species. Crows, by the way, have longer rearing and nurturing periods than other bird species. These "learning periods" are even longer than those observed in many mammal species. These nurturing periods can last up to a year and a half and enable the parental generation to pass along via a cultural information system extensive amounts of very functional survival information to their offspring.
American crows can be found residing in or moving through a great variety of ecological habitats. They seem to prefer a broad functional range that includes both fields (for grasses and seeds and for small vertebrate and invertebrate prey species) and woodlands (for night roosts and for protection). Human agricultural systems are especially favored by the American crow. Their negative impacts on grain crops etc can be extensive. It is estimated that in the United States the summed American crow population numbers over three billion individuals! Many states (including Pennsylvania) allow hunting of the crow to try to control its numbers.
Crows are thought to mate for life and engage in a richly complex set of courtship displays. Breeding flocks, as previously mentioned, are small and typically consist of a breeding pair and the offspring from the previous years. Nests are constructed in the crotches of trees ten to seventy feet above the ground. Both the male and the female participate in nest construction. The nest is 22 to 26 inches in diameter and is constructed of a variety of plant debris (sticks, vines, coarse grasses etc) and lined with softer materials (like hair, finer grasses and feathers). Broods consist of 4 to 5 eggs which hatch after 18 days of incubation. At five weeks the nestlings are ready to fledge. A breeding pair can have two broods per season.
Crows eat a great variety of foods. Invertebrates (like grasshoppers, grubs, earthworms, caterpillars, etc) are consumed as they become seasonally abundant. Vertebrates (bird eggs, small birds, rodents) are eaten opportunistically or may even be actively hunted. Crows also consume carrion and are active scavengers of human garbage. Crows utilize their excellent vision to find and obtain their food. While hunting and feeding individuals of the flock take specialized jobs (some functioning lookouts, for example, while others of the flock feed). Vocal communications between individuals of the flocks are critical to the overall success of the foraging group. Complex hunting behaviors have also been observed in crows. Some these include mobs of crows driving rabbits from a field across a roadway. A percentage of the driven rabbits were hit by cars and were then consumed by the crows. Crows have also been observed actively interfering with other predators (like river otters) to distract them from their captured prey which the crows then appropriate for their own consumption. These behaviors are further examples of the group dynamics and extreme intelligence of this avian species.