The American crow is the “default” crow across most of North America. It overlaps broadly with the common raven, and to a lesser extent with the Chihuahuan raven, fish crow, and northwestern crow. Study of vocalizations, bill structure and size, tail shape, and overall structure of this species will greatly aid in the identification of other crows and ravens. Regional variation in size of the American crow poses challenges, particularly in the northwest. Polytypic. Length 17.5" (45 cm).
Geographic Variation Four poorly defined subspecies generally recognized. While variation is largely clinal, differences between extremes are apparent. Northern brachyrhynchos and eastern and southern palus are essentially inseparable. Florida Peninsula pascuus has relatively long bill, long tarsus, and large feet. Also differs in behavior, never forming flocks; not found in urban areas and has more extensive vocal repertoire. The smaller western subspecies hesperis has been suggested to be more closely related to the Northwestern crow than to subspecies of American crow—the entire relationship between the American and Northwestern crow remains unclear.
Similar Species Compare with very similar fish crow and nearly identical Northwestern crow (both most easily separated by voice), common and Chihuahuan ravens.
Voice Call: adult’s familiar caw generally well known. Voice of hesperis generally lower pitched than other subspecies. Juvenile’s begging call is higher pitched, nasal, and resembles the call of the fish crow.
Status and Distribution Common to abundant. Breeding: a variety of habitats, particularly open areas with scattered trees. Migration and Dispersal: diurnal migrant. In spring, arrive mid-February–late April. Fall migration generally more protracted than in spring. Most depart north-central British Columbia and Alberta by late September; peak in Great Lakes early October–mid-November. Uncommon to rare migrant and winter visitor in deserts of the West. Winter: throughout much of the lower 48. Vagrant: casual to southwestern Arizona, southwestern Texas, northwestern Sonora, Mexico.
Population Expanded with clearing of forests and planting of woodlots in prairies. Many populations experienced dramatic declines with the spread of West Nile virus early this century. Nevertheless long-term populations generally stable.
http://samersam6.maktoobblog.com/page/2/
Identification Largest crow in North America, with uniformly black plumage and fan-shaped tail. Bill is larger than other American crows, but distinctly smaller than either raven. On rare occasions individuals show white patches in wings. Juvenile: brownish cast to feathers; grayish eye, and fleshy gape (quickly darkening after fledging). Immature: tends to show worn brownish wings that contrast with fresher black wing coverts. Flight: steady, with low rowing wingbeats. Does not soar.Geographic Variation Four poorly defined subspecies generally recognized. While variation is largely clinal, differences between extremes are apparent. Northern brachyrhynchos and eastern and southern palus are essentially inseparable. Florida Peninsula pascuus has relatively long bill, long tarsus, and large feet. Also differs in behavior, never forming flocks; not found in urban areas and has more extensive vocal repertoire. The smaller western subspecies hesperis has been suggested to be more closely related to the Northwestern crow than to subspecies of American crow—the entire relationship between the American and Northwestern crow remains unclear.
Similar Species Compare with very similar fish crow and nearly identical Northwestern crow (both most easily separated by voice), common and Chihuahuan ravens.
Voice Call: adult’s familiar caw generally well known. Voice of hesperis generally lower pitched than other subspecies. Juvenile’s begging call is higher pitched, nasal, and resembles the call of the fish crow.
Status and Distribution Common to abundant. Breeding: a variety of habitats, particularly open areas with scattered trees. Migration and Dispersal: diurnal migrant. In spring, arrive mid-February–late April. Fall migration generally more protracted than in spring. Most depart north-central British Columbia and Alberta by late September; peak in Great Lakes early October–mid-November. Uncommon to rare migrant and winter visitor in deserts of the West. Winter: throughout much of the lower 48. Vagrant: casual to southwestern Arizona, southwestern Texas, northwestern Sonora, Mexico.
Population Expanded with clearing of forests and planting of woodlots in prairies. Many populations experienced dramatic declines with the spread of West Nile virus early this century. Nevertheless long-term populations generally stable.
Source:http://aullori.wordpress.com/2008/04/07/the-american-crow/
—From the National Geographic book Complete Birds of North America, 2006