The American Crow (Corvus brachyrhynchos): Morphology, Habitat and Evolutionary History
| Non-Breeding social system | Breeding System | Summary | References | Davidson College |
| The American Crow, familiar across North America, is an extremely adaptable and intelligent bird. The American Crow fits the corvid pattern of gregarious and vocal behavior. They are quite intelligent, when asked about their intelligence, McGowan responded that crows are "smarter than many undergraduates, but probably not as smart as ravens". They have even matched primates in some intelligence tests; they may owe this ability to their habit of caching food, which requires excellent spatial memory (McGowan, 2001). In one case, one crow pecked at a river otter, causing it to drop its fish and attack the offending crow; the other crows then darted in and stole the fish (Verbeek and Caffrey 2002). I myself have observed a crows harass a Northern Mockingbird, drawing it from its nest while the other darted in and stole in egg. This intelligence also manifests itself in play behavior, including such games as tug-of-war and “log-rolling on small round objects (Verbeek and Caffrey 2002). |
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| McGowan (2001) writes that crows and their allies have been “specialized to be generalists.” Their morphology supports both terrestrial and aerial modes. Their long legs allow crows to be efficient hoppers and walkers on the ground. They make use of their strong bills to poke around in the ground and leaf litter, forage for fruits, tear into garbage bags and hunt small prey items. At the same time, broad, slotted wings and long tails make crows efficient aerialists (McGowan 2001). This morphology has allowed them to exploit many kinds of habitats. A partial list of crow foraging behavior includes comically pursuing flying insects, using the bill as a shovel to dig, wading belly-deep to fish, creating shade with their wings to create shade to attract insects, and caching eggs. In one experiment, white lab mice were released in a field with three crows. After curiously examining them, the crows proceeded to hunt and cache 79 mice in 127 minutes (Verbeek and Caffrey 2002). |
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Crows and other members of the family Corvidae are part of an lineage of birds including the shrikes and vireos that originated in Australia after the continent’s separation from the Asian landmass (Rowley 1998). There are several species of Corvus in North America. All four (American, Northwestern, Fish, Tamaluipas) are very similar and are best identified by voice. The American Crow can be loosely divided into four subspecies: C. b. hesperis, C. b. brachyrynchos, C. b. paulus, and C. b. pascuus. Crows can be found just about anywhere in North America, though they avoid desert and deep forests. Their only requirements are having relatively open areas to forage in and scattered areas of trees to roost in and provide protection from the elements and predators. Despite severe persecutions (Aldous 1944; see picture), the clearing of eastern forests and an huge increase in agriculture has actually allowed crow populations to increase (Verbeek and Caffrey 2002). This large population, with a wide geospatial distribution, likely has significant variation in behavior; for this reason, Verbeek and Caffrey (2002) caution against drawing conclusions about the whole species from individual, regional populations.
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| Note: This webpage was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2007; please direct any questions, comments or threats to Howell Burke or Verna Case. |