American crow

(Corvus brachyrhynchos)

Compiled by Niyati Acharya

American Crows are large, all-black birds with hoarse, cawing voices. They are common sights in treetops, fields, roadsides, as well as in habitats ranging from open woods to beaches to town centers. The species feed on the ground, eat earthworms, insects, small animals, seeds, and fruit, as well as garbage, carrion, and chicks that they rob from nests. Their flight style is a unique, patient, methodical flapping that is rarely broken by glides.

American crows are highly adaptable birds. They are one of only a few species that have been observed modifying and using tools to obtain food.  They are highly social birds, more often seen in groups than alone, and will gather in groups to forage. When they are foraging, a few crows will be on the lookout.  If danger approaches, they sound an alarm.  

For most of the year, American crows leave their territory to roost and join large flocks, otherwise known as murders.  Winter roosts have numbered into tens of thousands.  According to the North American Breeding Bird Survey, the American crow population has slightly increased with the onset of deforestation. However, the species is sensitive to West Nile virus, which was introduced to North America in 1999. Virtually all crows that contract West Nile die within one week. Nevertheless, long-term populations are generally stable.

Crows and other members of the family Corvidae (corvids) are widely regarded as among the most intelligent bird species.  Many are capable of long-term human facial recognition, understanding and responding to reward inequity, assessing risk, tracking and remembering the actions of others, manufacturing rudimentary tools, and potentially possessing a theory of mind. Corvids are also capable of social learning.  American crows learn new dangers and keep track of predators by observing conspecific behavior.  Crows possess many of the characteristics required for high intelligence: they have high annual survivorship, live in fission-fusion social groups, and possess a large brain relative to their body size.  These qualities allow crows to amass and draw upon a great deal of experience (via individual and social learning) over the course of their long lives. Wing markings are also helpful for identification.

Most vertebrates, including American Crows, regularly encounter novel situations throughout their lives, and their ability to successfully navigate them directly benefits their survival and fitness. Researchers examined the factors affecting the ability of 27 wild-caught American crows to solve a common string-pulling task in a laboratory setting.  Their findings suggest that brain volume and possibly body condition may be factors in learning new tasks.  Crows can use social learning to refine their ability to obtain a novel food source, although they must initially learn to access it themselves

Sources include: Allaboutbirds.org, Holdenforests&gardens.org, National Library of Medicine

Photo credit:  Pearsall, Peter/USFWS, Warren Bielenberg/NPS, Courtney Celley/USFWS, Fuertes, Louis Agassiz/USFWS