Creature Feature: American Crow

The American crow (Corvus brachyrhynchos) might not look like much compared to its more menacing cousin of “Nevermore!” fame, the Common raven (Corvus corax), but behind those beady eyes lies a keen intelligence, a playful nature, and a particular knack for problem-solving. It is the largest crow species in North America and is highly adaptable, capable of thriving in virtually any environment with open space, perches, and a ready food supply.1

American crows have been observed on multiple occasions using and fashioning tools to acquire particularly tricky food items, and can even solve complicated series of puzzles for rewards. They can shape sticks of wood and wires into hooks to ‘fish’ for food in tubes, use cups to carry water, and drop items such as pieces of pine cones on unsuspecting prey.3 Interestingly, the New Caledonian crow (Corvus moneduloides), a fellow corvid, has been spotted on numerous occasions in Akita, Japan, dropping walnuts into street crosswalks to get the nuts to crack open by passing car tires, and then flying down while pedestrians are crossing to retrieve the tasty flesh.5

Despite their intelligence, crows have a mixed reputation in a number of ancient and contemporary cultures. Celtic tribes thought their war goddess Morrigan could appear in the shape of a crow. Some Native American tribes hold respect for the intelligence of the crow and have clans devoted to the animal, and the ancient Greeks thought the crow was a sign of their prophetic god Apollo and interpreted messages based on their flight patterns. Even within regions, the crow’s reputation can vary: in some parts of North America, low-flying crows are harbingers of illness and death, but in other parts, groups of crows bring good luck although a solitary crow is said to be unlucky. Even the whimsical name for a group of crows in common parlance is a “murder”, a term rooted in Middle Age venery, or hunting.8

Crow2
A murder of crows can often reach sizes of up to two million strong! [Source]
The crow’s reputation as a harbinger of doom and gloom may stem from their foreboding all-black plumage, distinctively gravelly “caw” call, and unsavory habit of scavenging meat from dead animals, but in reality, crows are mischievous opportunists and devoted family members. American crows have been seen distracting river otters to steal their food, nicking scraps from the nests of songbirds, and even eating from outdoor dog dishes!  American crows are omnivores, eating seeds, nuts, and berries, as well as the eggs and nestlings of many smaller passerines such as sparrows and robins. They also eat many insects, aquatic animals such as fish and turtles, as well as carrion and garbage, with which they are often associated. They are perpetual teenagers, holding territories with their families year-round and going out during the day as individuals to join flocks to forage for food in lieu of hanging out on street corners, sleeping in massive communal roosts of up to two million individuals.2

crow3
Crows have a wide diet breadth including seed, fruit, eggs, insects, small vertebrates, carrion, and even scraps thrown in the thrash. [Source]
American crows have also been known to make ‘friends’ with humans, bringing them gifts in exchange for food and becoming the unwitting stars of any number of funny Youtube videos taken by hapless homeowners visited by the playful birds. One notable recipient of crow friendship is a young girl in Seattle who received odd tokens from the birds in her backyard from the age of four, including one half of a ‘best friends’ pendant and a camera lens cap her family had lost nearby.7

The species is at a low conservation risk due to its high adaptability and large, stable population numbers of around 27 million individuals. However, the American crow is singularly susceptible to West Nile virus after its introduction to North America in 1999, and most crows die less than a week after exposure at a higher known rate than any other bird species.2 Crows residing in species-rich areas are far more likely to survive than those exposed populations in less biodiverse regions, demonstrating potential conservation implications for even a species of such low concern.4

crow4
Human west nile virus cases by county in 2016. The American crow is a reservoir for this mosquito-vectored virus and they succumb easily to the disease. [Source]
In Davis, California, crow roosts have been found to be a large reservoir for West Nile virus, which is transmitted by biting mosquitos. In 2004 and 2014, there were significant spikes of human cases of West Nile infection in the Davis community. According to Dr. William Reisen with the Center for Vectorborne Diseases at the UC Davis School of Veterinary Medicine, these spikes can be correlated with similar increases in the number of birds found that tested positive for the virus in those years. In 2004 alone, over 189 human cases were reported in Sacramento and Yolo counties, along with 87 confirmed infected birds.6 Research elucidating transmission dynamics between the mosquito vector and bird host will go a long way in helping to model disease outbreaks in human populations.

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Crows are extremely intelligent and perhaps with public awareness and conversation, age-old stigmas associated with this fascinating bird will slowly disappear. [Source]
Despite their intelligence and resourcefulness, the American crow might still seem quite common and unassuming. But who knows? The next time you meet one, you could end up with a new best friend. If you’re lucky, you might even get matching bracelets—just don’t get too close.

[By: Katherine Hopwood]


References

1“American Crow.” National Geographic, 4 May 2010. www.nationalgeographic.com/animals/birds/a/american-crow/.

2“American Crow Life History.” The Cornell Lab of Ornithology, 2017. https://www.allaboutbirds.org/guide/American_Crow/lifehistory

3Caffrey, Carolee. “Tool Modification and Use by an American Crow.” The Wilson Bulletin, 2000, v.112 no.2, pp. 283-284.

4“Counting Crows: The Impact of the West Nile Virus.” The Cornell Lab of Ornithology, 15 October 2010. https://www.allaboutbirds.org/counting-crows-the-impact-of-the-west-nile-virus/

5Gareth Huw Davies. “Bird Brains.” PBS, accessed 25 February 2018. http://www.pbs.org/lifeofbirds/brain/

6Garvey, Kathy Keatley. “UC Davis scientists targeting crows in war against West Nile virus.” UC Davis Veterinary Medicine, 8 September 2006. http://www.vetmed.ucdavis.edu/whatsnew/article2.cfm?id=1646

7Katy Sewall. “The girl who gets gifts from birds.” BBC News Magazine, 25 February 2015. http://www.bbc.com/news/magazine-31604026

8Wigington, Patti. “The Magic of Crows and Ravens.” Thought Co., 5 June 2017. https://www.thoughtco.com/the-magic-of-crows-and-ravens-2562511

Main featured image [Source]

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