American crow

The American crow (Corvus brachyrhynchos) is a large passerine bird species of the family Corvidae. It is a common bird found throughout much of North America. American crows are the New World counterpart to the carrion crow and the hooded crow. Although the American crow and the hooded crow are very similar in size, structure and behavior, their calls and visual appearance are different. The American crow, nevertheless, occupies the same ecological niche that the hooded crow and carrion crow do in Eurasia.

American crow
Corvus-brachyrhynchos-001.jpg
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Corvidae
Genus: Corvus
Species:
C. brachyrhynchos
Binomial name
Corvus brachyrhynchos
Brehm, 1822
Corvus brachyrhynchos distribution.png
Global range
Pair of crows chasing away a red-tailed hawk from their nest

From beak to tail, an American crow measures 40–50 cm (16–20 in), almost half of which is tail. Mass varies from about 300 to 600 g (11 to 21 oz). Males tend to be larger than females. The most usual call is CaaW!-CaaW!-CaaW!. Plumage is all black, with iridescent feathers. It looks much like other all-black corvids. They can be distinguished from the common raven (C. corax) because American crows are smaller; from the fish crow (C. ossifragus) because American crows do not hunch and fluff their throat feathers when they call; and from the carrion crow (C. corone) by size, as the carrion crow is larger and of a stockier build. They are very intelligent, and adaptable to human environments.

American crows are common, widespread, and susceptible to the West Nile virus, making them useful as a bioindicator to track the virus's spread. Direct transmission of the virus from crows to humans is impossible. They are considered an agricultural pest, and are subject to hunting and management.

Taxonomy and systematicsEdit

The American crow was described by German ornithologist Christian Ludwig Brehm in 1822.[2] Its scientific name means literally 'short-billed crow', from Ancient Greek βραχυ- brachy- ('short-') and ρυνχος rhynchos ('billed').[3]

A 2012 genetic analysis of the genus Corvus by Knud A Jønsson and colleagues using nuclear and mitochondrial DNA calculated that the American crow diverged from a lineage that gave rise to the collared, carrion and hooded crows around 5 million years ago.[4]

"American crow" has been designated the official name by the International Ornithologists' Union (IOC).[5]

SubspeciesEdit

 
Northwestern crow range map

The number of subspecies varies by authority, ranging between three and five. The unclear taxonomy of the northwestern crow, previously its own species, has complicated subspecies determinations. Subspecies differ in bill proportion and form a rough NE–SW clinal in size across North America. Birds are smallest in the far west and on the southern coast.[6][2]

  • C. b. brachyrhynchos (Brehm, 1822)eastern crow: northeastern United States, eastern Canada and surroundings. The nominate subspecies, and largest.
  • C. b. hesperis (Ridgway, 1887)western crow: western North America except the Arctic north, the Pacific Northwest and the extreme south. Smaller overall with a proportionally more slender bill[7] and low-pitched voice.
  • C. b. caurinus (Baird, 1858) northwestern crow: of the Pacific temperate rain forests was formerly considered a distinct species as C. caurinus, averaging smaller in size than other American crows with a distinctly hoarser call.[8] It forms a hybrid swarm with American crow (sensu stricto) in coastal Washington and British Columbia.[9] The American Ornithological Society lumped the northwestern crow with the American crow in 2020.[10] It is now considered a geographic variation within C. b. hesperis.[11]
  • C. b. pascuus (Coues, 1899)Florida crow: Florida. Mid-sized, short-winged, but decidedly long bill and legs.[7]
  • C. b. paulus (Howell, 1913)southern crow: southern United States. Smaller overall, bill also small.[12]

DescriptionEdit

An American crow making its distinctive call.
 
American crow - Brooklyn, NY
 
The skull of an American crow

The American crow is a large, distinctive bird with iridescent black feathers all over. Its legs, feet and bill are also black. They measure 40–53 cm (16–21 in) in length, of which the tail makes up about 40%. The wing chord is 24.5 to 33 cm (9.6 to 13.0 in), with the wingspan ranging from 85 to 100 cm (33 to 39 in). The bill length can be from 3 to 5.5 cm (1.2 to 2.2 in), varying strongly according to location. The tarsus is 5.5 to 6.5 cm (2.2 to 2.6 in) and the tail is 13.5 to 19 cm (5.3 to 7.5 in).[6] The body mass can vary from 316 to 620 g (11.1 to 21.9 oz). Males tend to be larger than females.[13][14]

 
Brooklyn Museum - American crow - John J. Audubon

The most usual call is a loud, short, and rapid caaw-caaw-caaw. Usually, the birds thrust their heads up and down as they utter this call. American crows can also produce a wide variety of sounds and sometimes mimic noises made by other animals, including other birds such as barred owls.[15]

Visual differentiation from the fish crow (C. ossifragus) is extremely difficult and often inaccurate. Nonetheless, differences apart from size do exist. Fish crows tend to have more slender bills and feet. There may also be a small sharp hook at the end of the fish crow's upper bill. Fish crows also appear as if they have shorter legs when walking. More dramatically, when calling, fish crows tend to hunch and fluff their throat feathers.[citation needed]

If seen flying at a distance from where size estimates are unreliable, the distinctly larger common ravens (C. corax) can be distinguished by their almost lozenge-shaped tail and their larger-looking heads. They also fluff their throat feathers when calling — like fish crows, only more so. Ravens also soar for extended periods, unlike crows, which rarely fly more than a few seconds without flapping their wings.[citation needed]

Crows have been noted to be intelligent. They have the same brain-weight-to-body ratio as humans. This has led to some studies that have identified that crows are self-aware and that young crows take time to learn from tolerant parents. While a human has a neocortex, the crow has a different area in their brain that is equally complex.[16][17]

 
A fledgling, of the Northwestern subtype

The average lifespan of the American crow in the wild is 7–8 years. Captive birds are known to have lived up to 30 years.[18]

Distribution and habitatEdit

The range of the American crow now extends from the Pacific Ocean to the Atlantic Ocean in Canada, on the French islands of Saint-Pierre and Miquelon, south through the United States, and into northern Mexico.[1] The increase in trees throughout the Great Plains during the past century due to fire suppression and tree planting facilitated range expansions of the American crow[19] as well as range expansions of many other species of birds.[20][21][22] Virtually all types of country from wilderness, farmland, parks, open woodland to towns and major cities are inhabited; it is absent only from tundra habitat, where it is replaced by the common raven. This crow is a permanent resident in most of the US, but most Canadian birds migrate some distances southward in winter. Outside of the nesting season these birds often gather in large (thousands or even millions[23]) communal roosts at night.[citation needed]

The American crow was recorded in Bermuda from 1876 onwards.[24]

Behavior and ecologyEdit

Studying the behavior of American crows is laborious due to the difficulty in catching them to band them, let alone catching them again. Thus much of their behavior, including daily routine, migration, molting, survivorship, age of first breeding, nestling development, nature of nesting helpers, and more remains poorly studied.[2]

DietEdit

 
American crow skeleton (Museum of Osteology)

The American crow is omnivorous. It will feed on invertebrates of all types, carrion, scraps of human food, fruits,[25] nuts such as walnuts and almonds, seeds, eggs and nestlings, stranded fish on the shore and various grains. American crows are active hunters and will prey on mice, young rabbits,[26] frogs, and other small animals. In the winter and autumn, the diet of American crows is more dependent on nuts and acorns. Occasionally, they will visit bird feeders.[27] The American crow is one of only a few species of bird that has been observed modifying and using tools to obtain food.[28]

Like most crows, they will scavenge at landfills, scattering garbage in the process. Where available, corn, wheat and other crops are a favorite food. These habits have historically caused the American crow to be considered a nuisance. However, it is suspected that the harm to crops is offset by the service the American crow provides by eating insect pests.[27]

ReproductionEdit

 
An American crow egg, in the collection of the Children's Museum of Indianapolis

American crows are socially monogamous cooperative breeding birds. Mated pairs form large families of up to 15 individuals from several breeding seasons that remain together for many years.[29] Offspring from a previous nesting season will usually remain with the family to assist in rearing new nestlings. American crows do not reach breeding age for at least two years.[30] Most do not leave the nest to breed for four to five years.[29]

The nesting season starts early, with some birds incubating eggs by early April.[31] American crows build bulky stick nests, nearly always in trees but sometimes also in large bushes and, very rarely, on the ground. They will nest in a wide variety of trees, including large conifers, although oaks are most often used. Three to six eggs are laid and incubated for 18 days. The young are usually fledged by about 36 days after hatching. Predation primarily occurs at the nest site and eggs and nestlings are frequently eaten by snakes, raccoons, ravens and domestic cats. Adults are less frequently predated, but face potential attack from great horned owls, red-tailed hawks, peregrine falcons and eagles. They may be attacked by predators such as coyotes or bobcats at carrion when incautious, although this is even rarer.[27][32]

West Nile virusEdit

American crows succumb easily to West Nile virus infection. This was originally a mosquito-borne African virus causing encephalitis in humans and livestock since about 1000 AD, and was accidentally introduced to North America in 1999, apparently by an infected air traveller who got bitten by a mosquito after arrival. It is estimated that the American crow population has dropped by up to 45% since 1999.[33] Despite this decline, the crow is considered a species of least concern.[34] The disease runs most rampant in the subtropical conditions which encourage reproduction of its mosquito vectors among which Culex tarsalis is most significant. Mortality rates appear to be higher than those in other birds, causing local population losses of up to 72% in a single season.[30][35] Because of this, American crows are a sentinel species indicating the presence of West Nile virus in an area. Crows cannot transmit the virus to humans directly.[18]

IntelligenceEdit

American crows, like other corvids, are highly cunning and inquisitive. They are able to steal food from other species, often in creative ways. One example shows a group of crows stealing a fish from a Northern river otter: one bird pecked the otter's tail to distract it while other birds swooped in and stole the fish.[2] They are able to use and modify tools.[36]

Relationship with humansEdit

Crows are a motif in human culture, often associated with death, thieves, graveyards, bad luck, and other negative connotations.[37]

Status and managementEdit

The intelligence and adaptability of the American crow has insulated it from threats, and it is instead considered an agricultural pest.[2] In 2012, BirdLife International estimated the American crow population to be around 31 million. The large population and vast range result in the least concern status for the American crow, meaning that the species is not threatened with extinction.[1]

Crows have been killed in large numbers by humans, both for recreation and as part of organized campaigns of extermination.[38] In Canada, American crows have no protections, aside from Quebec which bans their hunting during the nesting season.[2] Laws on their hunting vary throughout the United States. New Jersey allows for a limited hunting season, unless if they are agricultural pests in which case they may be killed. Oklahoma allows hunting even during the nesting season. In the first half of the 20th century, state sponsored campaigns dynamited roosting areas, taking large numbers of crows. A campaign in Oklahoma from 1934 to 1945 dynamited 3.8 million birds. The effect on populations was negligible and damage to agricultural crops did not decrease, and thus the campaign was halted as ineffective. In a study taking data from 1917 to 1999, intentional killings were the overwhelming cause of death for crows, accounting for 68% of all recovered bird bands.[2]

Non-deadly methods of managing crows are varied but usually limited in their effectiveness. High value crops may be netted, but this is cost prohibitive for most other crops. Frightening may be used to disperse crows, including loud noises from guns, fake hawks flown from balloons, fake owls that move with the wind, strips of reflective tape on fences, or recordings of crow distress calls. Poisoned baits are of limited effectiveness, as only the most toxic baits work, and those are generally unacceptable for use. Crows quickly learn to avoid the less-toxic baits, as the baits make crows sick. The actual effect of crows on agriculture has been poorly studied.[2] There is some suggestion that they may be a benefit to farmers, by eating insect pests and chasing off livestock predators like hawks.[37]

ReferencesEdit

  1. ^ a b c BirdLife International (2018). "Corvus brachyrhynchos". IUCN Red List of Threatened Species. 2018: e.T22705990A131945410. doi:10.2305/IUCN.UK.2018-2.RLTS.T22705990A131945410.en. Retrieved 19 November 2021.
  2. ^ a b c d e f g h Verbeek, N. A.; Caffrey, Carolee (August 2021). Poole, A. F.; Gill, F. B. (eds.). "American Crow (Corvus brachyrhynchos) version 1.1". Birds of the World. Cornell Lab of Ornithology. doi:10.2173/bow.amecro.01.1. S2CID 241865621.
  3. ^ Liddell, Henry George; Scott, Robert; Stuart-Jones, Henry and McKenzie, Roderick: (1980): A Greek-English Lexicon (abridged ed.). Oxford University Press, Oxford, UK. ISBN 0-19-910207-4.
  4. ^ Jønsson, Knud A.; Fabre, Pierre-Henri; Irestedt, Martin (2012). "Brains, tools, innovation and biogeography in crows and ravens". BMC Evolutionary Biology. 12: 72. doi:10.1186/1471-2148-12-72. PMC 3480872. PMID 22642364.
  5. ^ Gill, Frank; Donsker, David, eds. (2021). "Crows, mudnesters, melampittas, Ifrit, birds-of-paradise". World Bird List Version 11.2. International Ornithologists' Union. Retrieved 26 October 2021.
  6. ^ a b Madge, Steve & Burn, Hilary (1994): Crows and jays: a guide to the crows, jays and magpies of the world. A&C Black, London. ISBN 0-7136-3999-7.
  7. ^ a b Goodwin & Gillmor (1976): p. 87
  8. ^ Dick, Gary Owen (2007): American Crow. Whatbird.com – Field Guide to Birds of North America. identify.whatbird.com/obj/103/_/American_Crow.aspx Retrieved 2007-October-18.
  9. ^ Slager, David L.; Epperly, Kevin L.; Ha, Renee R.; Rohwer, Sievert; Wood, Chris; Hemert, Caroline; Klicka, John (2020). "Cryptic and extensive hybridization between ancient lineages of American crows". Molecular Ecology. 29 (5): 956–969. doi:10.1111/mec.15377. ISSN 0962-1083. PMID 32034818. S2CID 211064373.
  10. ^ Chesser, R Terry; Billerman, Shawn M; Burns, Kevin J; Cicero, Carla; Dunn, Jon L; Kratter, Andrew W; Lovette, Irby J; Mason, Nicholas A; Rasmussen, Pamela C; Remsen, J V; Stotz, Douglas F (2020-07-24). "Sixty-first Supplement to the American Ornithological Society's Check-list of North American Birds". The Auk. 137 (3): ukaa030. doi:10.1093/auk/ukaa030. ISSN 0004-8038.
  11. ^ "Corvus brachyrhynchos hesperis (caurinus or occidentalis) (American Crow (caurinus or occidentalis)) - Avibase". avibase.bsc-eoc.org. Retrieved 2021-10-19.
  12. ^ Goodwin & Gillmor (1976) p. 88.
  13. ^ Kilham, Lawrence. The American Crow and the Common Raven. p. 52
  14. ^ American Crow, Life History, All About Birds – Cornell Lab of Ornithology. Allaboutbirds.org. Retrieved on 2013-03-06.
  15. ^ Lawrence Kilham (October 1990). The American Crow and the Common Raven. Texas A&M University Press. pp. 62–. ISBN 978-0-89096-466-8.
  16. ^ Amanda Heidt. "Like humans, these big-brained birds may owe their smarts to long childhoods".
  17. ^ Chris Baraniuk. "Crows have long been considered cunning. But their intelligence may be far more advanced than we ever thought possible".
  18. ^ a b Connecticut Department of Environmental Protection (2001): American Crow Fact Sheet Archived November 5, 2006, at the Wayback Machine. Version of 2001. Retrieved 2006-October-25.
  19. ^ Houston S. 1977. Changing patterns of Corvidae on the prairies. Blue Jay 35:149–155.
  20. ^ Livezey KB. 2009a. Range expansion of Barred Owls, part I: chronology and distribution. American Midland Naturalist 161:49–56.
  21. ^ Livezey KB. 2009b. Range expansion of Barred Owls, part 2: facilitating ecological changes. American Midland Naturalist 161:323–349.
  22. ^ Livezey KB. 2010. Killing barred owls to help spotted owls II: implications for many other range-expanding species. Northwestern Naturalist 91:251–270.
  23. ^ Di Dilvestro, Roger. "Something To Crow About". National Wildlife Federation.
  24. ^ Long, John L. (1981). Introduced Birds of the World: The worldwide history, distribution and influence of birds introduced to new environments. Terrey Hills, Sydney: Reed. p. 354. ISBN 0-589-50260-3.
  25. ^ "Corvus brachyrhynchos (American crow)".
  26. ^ "Corvus brachyrhynchos (American crow)".
  27. ^ a b c C. Parr (2005). "Corvus brachyrhynchos". Animal Diversity Web. Retrieved 13 September 2015.
  28. ^ Caffrey, Carolee (2000). "Tool Modification and Use by an American Crow". Wilson Bull. 112 (2): 283–284. doi:10.1676/0043-5643(2000)112[0283:TMAUBA]2.0.CO;2. S2CID 86124230.
  29. ^ a b Roger Segelken: Tree-climbing researcher knows exactly how far the crow flies Archived September 16, 2006, at the Wayback Machine Cornell Chronicle. Retrieved 2006-October-25,
  30. ^ a b Cornell Lab of Ornithology (2002): Bird Guide – American Crow. Retrieved 2006-October-24.
  31. ^ Henninger, W.F. (1906). "A preliminary list of the birds of Seneca County, Ohio" (PDF). Wilson Bulletin. 18 (2): 47–60.
  32. ^ Johnson, Ron American Crows Archived 2017-07-16 at the Wayback Machine. Internet Center for Wildlife Damage Management
  33. ^ LaDeau, Shannon L.; Kilpatrick, A. Marm; Marra, Peter P. (2007). "West Nile virus emergence and large-scale declines of North American bird populations". Nature. 447 (7145): 710–713. Bibcode:2007Natur.447..710L. doi:10.1038/nature05829. PMID 17507930. S2CID 4337661.
  34. ^ Deen, David (December 12, 2012). "The crow – a sociable bird with a long memory". The Chronicle. Barton, Vermont. p. 34.
  35. ^ Caffrey, Carolee; Smith, Shauna C.R.; Weston, Tiffany J. (2005). "West Nile Virus Devastates an American Crow Population". Condor. 107 (1): 128–132. doi:10.1650/7646. S2CID 85419982.
  36. ^ Caffrey, Carolee (June 2000). "Tool Modification and Use by an American Crow". The Wilson Bulletin. 112 (2): 283–284. doi:10.1676/0043-5643(2000)112[0283:TMAUBA]2.0.CO;2. ISSN 0043-5643. S2CID 86124230.
  37. ^ a b Sullivan, Emily. "The Glorious American Crow - Romanticism at SU". Archived from the original on 2020-09-28. Retrieved 2021-10-23.
  38. ^ Campbell, Robert Wayne & Canadian Wildlife Service (1997). "American Crow". The Birds of British Columbia: Passerines : flycatchers through vireos. UBC Press. p. 227. ISBN 978-0-7748-0572-8.

BibliographyEdit

  • Goodwin, Derek & Gillmor, Robert (1976): Crows of the World (1st ed.). University of Washington Press, Seattle.

External linksEdit