Overview

Distribution

occurs (regularly, as a native taxon) in multiple nations

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National Distribution

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

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Global Range: (250-20,000 square km (about 100-8000 square miles)) RESIDENT: Pacific coast, mainly from south-coastal and southeastern Alaska south through western British Columbia to northwestern Washington (Puget Sound vicinity) (AOU 1983).

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Range

Kodiak I. and coastal s Alaska to sw Washington.

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Geographic Range

Corvus caurinus lives only along the coast of the northeastern Pacific Ocean between southern Alaska and the northern tip of Washington.

Biogeographic Regions: nearctic (Native )

  • Verbeek, N., R. Butler. 1999. Northwestern Crow (Corvus caurinus). The Birds of North America, 407: 1-23.
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Physical Description

Morphology

Physical Description

Northwestern crows are mid-sized birds, 41.9 to 44.5 cm long and weighing 340 to 440 g. They have a wingspan of about 99 cm and their feathers are iridescent black with bluish-violet on their head, neck, back, wings, and tail. Their eyes are a smokey brownish-grey color, and their bills are glossy and stout though smaller and less powerful than those of common ravens (Corvus corax). They also have bristlelike feathers covering the nares. Corvus caurinus has thick, black legs with large scales on the front side only. When at rest, the tips of their folded wings do not reach the tip of the tail, which has slightly rounded ends. The sexes look alike, though the male is slightly larger than the female.

Immature C. caurinus between 3 to 15 months are also black, but have less iridescence than adults. Their back, wing and tail feathers fade gradually from black to brown. Juveniles from 1 to 3 months have looser, fluffier feathers than adult or immature C. caurinus and their feathers are a dull black. They have blue eyes.

Corvus caurinus can be distinguished from American crows (Corvus brachyrhynchos) because it is about 10% smaller, with smaller feet. It is also smaller than common ravens (C. corax), and while C. corax has a wedge-shaped tail, the tail of C. caurinus is squarish. Corvus corax also has shaggy throat-feathers which C. caurinus lacks.

Range mass: 440 to 340 g.

Range length: 44.5 to 41.9 cm.

Average wingspan: 99 cm.

Sexual Dimorphism: male larger

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Size

Length: 41 cm

Weight: 415 grams

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Type Information

Cotype for Corvus caurinus Baird in Baird et al.
Catalog Number: USNM A9511
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Birds
Sex/Stage: unknown; Adult
Preparation: Skin: Whole
Collector(s): C. Kennerly
Year Collected: 1857
Locality: Orcas Island, San Juan, Washington, United States, North America
  • Cotype: Baird. 1858. Rep. Expl. And Surv. R.R. Pac. 9: xliii, 559 (in key), 569.
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Cotype for Corvus caurinus Baird in Baird et al.
Catalog Number: USNM A10310
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Birds
Sex/Stage: unknown; Adult
Preparation: Skin: Whole
Collector(s): G. Suckley
Year Collected: 1856
Locality: Fort Steilacoom, Pierce, Washington, United States, North America
  • Cotype: Baird. 1858. Rep. Expl. And Surv. R.R. Pac. 9: xliii, 559 (in key), 569.
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Cotype for Corvus caurinus Baird in Baird et al.
Catalog Number: USNM A10307
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Birds
Sex/Stage: unknown; Adult
Preparation: Skin: Whole
Collector(s): G. Suckley
Year Collected: 1856
Locality: Fort Steilacoom, Pierce, Washington, United States, North America
  • Cotype: Baird. 1858. Rep. Expl. And Surv. R.R. Pac. 9: xliii, 559 (in key), 569.
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Cotype for Corvus caurinus Baird in Baird et al.
Catalog Number: USNM A10306
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Birds
Sex/Stage: unknown; Adult
Preparation: Skin: Whole
Collector(s): J. Cooper
Year Collected: 1854
Locality: Shoalwater Bay, Pacific, Washington, United States, North America
  • Cotype: Baird. 1858. Rep. Expl. And Surv. R.R. Pac. 9: xliii, 559 (in key), 569.
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Ecology

Habitat

Comments: Coastal tidelands near coniferous woodland or forest edge, foraging also in adjacent croplands and around human habitation (AOU 1983). BREEDING: Nests in crotches of low trees and bushes, 2.5-6 m above ground (Terres 1980). May also nest under rocks, bushes, or fallen trees near the ocean.

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Habitat and Ecology

Systems
  • Terrestrial
  • Freshwater
  • Marine
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Corvus caurinus lives mainly in coastal regions near intertidal zones, but can be found along large rivers as far as 120 km inland. They are typically near, but not necessarily in, forested regions and will pull back into the forest edge during harsh weather conditions in winter. Northwestern crows are also likely to live near seabird colonies and refuse dumps. They have also been found living in river deltas, coastal bays, coastal villages, towns and cities, as well as on farmland. They can be found at elevations up to 1700 m.

Range elevation: 0 to 1700 m.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: forest

Aquatic Biomes: coastal

Other Habitat Features: urban ; suburban ; agricultural ; riparian

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Depth range based on 3116 specimens in 1 taxon.

Environmental ranges
  Depth range (m): 0 - 0
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Migration

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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Trophic Strategy

Comments: Eats saltwater invertebrates (e.g., snails, amphipods, bivalves), obtained on beaches and mudflats; carrion and refuse (dead fish, scraps); seabird eggs; insects and their larvae (e.g., grubs and grasshoppers) obtained in inland fields; fruits.

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Food Habits

Northwestern crows are omnivorous scavengers. They can and will eat almost anything they can find. Their diet ranges from small invertebrates, to human garbage, to fruit, depending on what’ is available. Along coasts they feed mainly on clams (Venerupis philippinarum and Protothaca staminea) crustaceans and sand dollars (Dendraster excentricus). The crows pick these animals up, fly high into the air and drop them on rocks in order to break them open. They have also been known to eat sea urchins (Strongylocentrotus purpuratus) off of rocks and to steal eggs and nestlings from peregrine falcons (Falco peregrinus) and cormorants (family Phalacrocoracidae), among others. Blackberries are an important part of their diet, as are many forms of carrion such as fish, dead seals, dead birds, roadkill and dead insects from the grills of cars.

They can be seen walking along the shore, digging through the sand for clams, stabbing the ground in search of insects and wading in shallow tide pools. They have also been known to root through garbage cans and landfills.

Corvus caurinus will also cache food in the morning and evenings. Saved items include clams, cormorant eggs, crabs and fish. Cached food is typically retrieved within 24 hours. They also transport cached food for young and incubating females. Food caching seems to take place mainly at the beginning of the breeding season during high tide. It is believed that one main function of caching food is that it guarantees food for the female and nestlings at a time when food could become scarce. Corvus caurinus caches food in vegetation and along rocks. They most often attempt to bury the food and seem to memorize its location in order to find it again.

Animal Foods: birds; mammals; amphibians; reptiles; fish; eggs; carrion ; insects; terrestrial non-insect arthropods; mollusks; aquatic crustaceans; echinoderms

Plant Foods: seeds, grains, and nuts; fruit

Foraging Behavior: stores or caches food

Primary Diet: omnivore

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Associations

Ecosystem Roles

Corvus caurinus feeds on many different organisms, both living and dead. It eats many of the species that inhabit northern tide pools and cleans up carrion and refuse in all of its habitats. It is prey to some large sea birds and some smaller vertebrates feed on C. caurinus nestlings. Nestlings and adults serve as hosts to louse flies, bird blow fly larvae (Protocaliphora braueri), fleas Ceratophyllus niger, and feather louse Myrsidea interrupta.

Blackberries are also an important food for C. caurinus and it acts as a disperser of blackberry seeds.

Ecosystem Impact: disperses seeds; biodegradation

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Predation

As a social animal, C. caurinus relies greatly on roosting partners for protection. They alert one another to predators with calls and then mob the potential predator and create a deafening noise by calling together. They tend to perch above predators and call down at them. They have been seen mobbing northern harriers (Circus cyaneus), hawks (Accipiter striatus and Buteo jamaicensis) , owls (Tyto alba, Asio flammeus and Asio otus), gray squirrels (Sciurus carolinensis), domestic cats (Felis silvestris), dogs (Canis lupus familiaris) and people. They also chase young birds, juvenile squirrels and raccoons (Procyon lotor). Many predators, such as garter snakes (genus Thamnophis), other birds, and possibly gray squirrels, are primarily a threat to nestlings and fledglings, these animals are attacked, chased or mobbed by the parents.

Predators of C. caurinus include: northern harriers (Circus cyaneus), sharp-shinned hawks (Accipiter striatus), red-tailed hawks (Buteo jamaicensis), owls (Tyto alba, Asio flammeus and Asio otus), gray squirrels (Sciurus carolinensis), domestic cats (Felis silvestris), dogs (Canis lupus familiaris), raccoons (Procyon lotor), northern goshawks (Accipiter gentilis), garter snakes (genus Thamnophis), Cooper's hawks (Accipiter cooperii) and bald eagles (Haliaeetus leucocephalus).

Known Predators:

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Known predators

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Known prey organisms

Corvus caurinus preys on:
Actinopterygii
Mollusca
Arthropoda
Echinodermata
Crustacea
Insecta
Amphibia
Reptilia
Aves
Mammalia

This list may not be complete but is based on published studies.
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Life History and Behavior

Behavior

Communication and Perception

Northwestern crows C. caurinus communicate mainly with calls. They have a variety of calls with meanings that range from threatening territorial defense calls to begging or feeding calls. Males have a specific call that they use to signal to brooding females that they are bringing food and she should come get some. They are very vocal in roosting groups and use warning calls and mob calls that will quickly bring the whole community together in order to scare off a would-be predator. They also engage in some visual displays, mostly to declare dominance, territory rights and to signal willingness to mate.

Communication Channels: visual ; acoustic

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Life Expectancy

Lifespan/Longevity

Corvus caurinus typically lives about 12 years in the wild, if it fledges. The longest known lifespan is 17 years. About 10% of eggs fail to hatch and many hatchlings either starve or are killed before they leave the nest. Some fledglings in coastal territories fall into the ocean and drown or are killed by neighboring colonies of gulls. Disease accounts for few deaths in C. caurinus populations. The main known cause of death is recreational shooting in British Columbia, but food availability is probably a large factor in determining population sizes. Corvus caurinus are not kept in captivity.

Range lifespan

Status: wild:
17 (high) years.

Average lifespan

Status: wild:
12 years.

Average lifespan

Status: wild:
200 months.

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Lifespan, longevity, and ageing

Maximum longevity: 16.7 years (wild)
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Reproduction

Nests May-June. Clutch size 4-5. Frequently nests in small loose colonies.

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It is not known when northwestern crows (Corvus caurinus) form breeding pairs, but it is most likely sometime in their second year, prior to the breeding season. If a courtship display exists, it is very subtle and has not been observed. However, prior to copulation, the male droops, spreads his wings and tail, points his bill down and quivers his wings and tail while exposing nictitating membranes (a transparent inner eyelid in birds). The female has a similar display, but she crouches and quivers her tail rapidly.

Corvus caurinus has been known to participate in cooperative breeding. A mated pair will sometimes keep one of their offspring from the previous season (who has not yet reached sexual maturity) with them on their breeding territory. The juvenile bird helps the male protect the territory, hide food, and, very infrequently, gather food for the nestlings. A breeding pair does not always have a helper; when they do they only have one and it is always one of their offspring.

Mating System: monogamous ; cooperative breeder

Young Corvus caurinus probably reach sexual maturity between 15 and 20 months. They copulate and begin building nests from early February through late March. Northwestern crows breed once yearly, but they will renest if disturbed early in the season. The female selects a place to build the nest, normally in or under trees, shrubs, blackberry tangles, or tall grass. Nest-building occurs only during daylight hours and in good weather. Nests are built with branches broken off of trees, grass and moss as well as other objects and soil. Corvus caurinus line their nests with moss, gull and crow feathers and sheep's wool, among other things.

A female C. caurinus typically lays 3 to 6 eggs per breeding season, laying one egg a day, almost always before 8:00 AM. Eggs are pale bluish with darker brown spots and are subelliptical to oval. They have a smooth, slightly glossy surface and are about 40 mm long and 28 mm wide.

Incubation most likely begins on the second day, and is performed by the female only. The incubation period is about 18 days; during this time the male feeds the female, most often at a small distance from the nest. After the eggs have hatched, female C. caurinus begin feeding the hatchlings.

Corvus caurinus typically leave the nest permanently at about 31 days. All of the chicks leave the nest on the same day and stay in nearby trees and shrubs, making short flights when their parents are away. They begin exploring nearby territories between 10 and 14 days and begin feeding themselves as early as 55 days after hatching. Parent C. caurinus will feed fledglings until they are 77 days old.

Breeding interval: Northwestern crows breed once yearly, but they will renest if disturbed early in the season.

Breeding season: Corvus caurinus copulate and begin building nests from early February through late March.

Range eggs per season: 6 to 3.

Range time to hatching: 20 to 17 days.

Range fledging age: 35 to 29 days.

Average time to independence: 77 days.

Range age at sexual or reproductive maturity (female): 15 to 20 months.

Range age at sexual or reproductive maturity (male): 15 to 20 months.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization

Average eggs per season: 4.

Adult C. caurinus build nests for their young, then lay eggs. The female broods the altricial young for about 18 days before devoting all of her time to gathering food and feeding them. The male, and sometimes a helper, will bring food from the time they hatch, until about 77 days after hatching. Young leave the nest at about 31 days but still rely on their parents for food as they can only make short flights. They begin to feed on their own starting around 55 days and parents generally stop feeding them at 77 days. Parent birds protect their offspring throughout this time. Immature C. caurinus associate with roosting groups of adults and feed near them for the first year or two, probably to pick up their leftovers and learn the intricacies of feeding.

Parental Investment: no parental involvement; altricial ; pre-hatching/birth (Protecting: Female); pre-weaning/fledging (Provisioning: Male, Female, Protecting: Male, Female); pre-independence (Provisioning: Male, Female, Protecting: Male, Female); post-independence association with parents

  • Verbeek, N., R. Butler. 1999. Northwestern Crow (Corvus caurinus). The Birds of North America, 407: 1-23.
  • James, P., N. Verbeek. 1983. The food storage behavior of the northwestern crow Corvus caurinus. Behaviour, 85 (3-4): 276-291.
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Molecular Biology and Genetics

Molecular Biology

Barcode data: Corvus caurinus

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 4 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNAATGCCAATCATAATCGGAGGATTTGGAAACTGACTAGTCCCTCTAATGATTGGTGCCCCAGACATAGCATTCCCACGAATAAACAACATAAGCTTCTGACTCCTCCCACCCTCCTTCCNTCTCCTTCTAGCCTCTTCCACAGTAGAAGCAGGAGCAGGAACAGGATGAACTGTGTACCCGCCACTAGCTGGCAACCTAGCCCACGCTGGAGCCTCAGTCGACCTAGCCATCTTCTCGCTACATCTAGCAGGTATCTCCTCCATCCTAGGGGCAATTAACTTCATCACCACTGCAATTAACATAAAACCCCCAGCCCTCTCACAATACCAAACCCCTCTGTTCGTATGATCCGTACTAATTACCGCAGTACTACTCCTTCTCTCCCTACCTGTACTTGCTGCCGGAATTACTATGCTTCTAACAGACCGTAACCTCAACACCACATTCTTCGATCCAGCAGGAGGAGGAGACCCAGTACTATACCAACACCTGTTCTGATTCTTCGGACATCCTGAATTGNAAATCCTAATTCTA
-- end --

Download FASTA File

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Statistics of barcoding coverage: Corvus caurinus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 4
Specimens with Barcodes: 4
Species With Barcodes: 1
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Conservation

Conservation Status

National NatureServe Conservation Status

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

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NatureServe Conservation Status

Rounded Global Status Rank: G5 - Secure

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IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2012

Assessor/s
BirdLife International

Reviewer/s
Butchart, S. & Symes, A.

Contributor/s

Justification
This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
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This species is protected by the US Migratory Bird Treaty Act. Overall, (C. caurinus) has benefited from human contact because humans clear out deep forests creating more of the open, forest fringe which these crows thrive in.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

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Population

Population Trend
Increasing
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Relevance to Humans and Ecosystems

Benefits

Economic Importance for Humans: Negative

Northwestern crows have been known to feed on crops.

Negative Impacts: crop pest

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Economic Importance for Humans: Positive

Corvus caurinus provides an important cleaning service to humans. It keeps shorelines and riversides free of refuse and carrion. It also plays an important role in keeping tide pool ecosystems in check. Studies show that predatory sea birds, including C. caurinus are a significant factor in controlling sea urchin populations. Northwestern crows hold down populations of clams and crabs, preventing overpopulation and maintaining biodiversity in the ocean and intertidal zones.

Positive Impacts: controls pest population

  • Robinette, R., C. James. 1997. The significance of fishing by Northwestern Crows. The Wilson Bulletin, 109(4): 748-749.
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Wikipedia

Northwestern crow

The northwestern crow (Corvus caurinus) is an all-black passerine bird of the crow genus native to the northwest of North America. It is very similar to the more western forms of the widespread American crow (Corvus brachyrhynchos), but it averages slightly smaller (33–41 cm in length) with proportionately smaller feet and a slightly more slender bill. This taxon is reliably identified by range only.

Taxonomy[edit]

This species was described by Spencer Fullerton Baird in 1858.[2] The American Ornithologists' Union considers it closely related to the American crow, and it may be conspecific.[2] Hybrids with American crow have been reported but not confirmed.[3]

Description[edit]

This species plumage is virtually identical to American crow.[4] A percentage may be distinguished by in-hand criteria such as smaller wing chord and tail length, shorter tarsus, and smaller bill.[3] Percentages increase when sex of animal is known.[3] Like the American crow, the sexes look the same.[3] Older birds in breeding condition may be reliably sexed by in-hand criteria such as cloacal protuberance (male) or by brood patch (female).[3] Younger birds may not attain breeding condition as they assist at the nest.[3]

Distribution and habitat[edit]

This species occurs in coastal regions and offshore islands of southern Alaska, south through British Columbia to Washington state. Beaches and shorelines are the principal forage areas. It can often be seen in and around urban areas.

Behaviour[edit]

Diet[edit]

Very similar to that of the fish crow; the northwestern crow eats stranded fish, shellfish, crabs and mussels, and also searches through refuse containers for suitable food items. It has been seen to fly into the air with mussels and drop them onto hard surfaces to break them open. It also regularly eats insects, other invertebrates, and various fruits (especially berries). It raids other birds' nests to eat eggs and hatchlings.

Predators[edit]

An incomplete list includes cats, raccoons, raptors and ravens. The crows often gather in large groups to mob these predators.

Nesting[edit]

Generally solitary, but sometimes built in association with a few other individuals in small, loose colonies in trees or sometimes large bushes. Very rarely, it will nest on cliffs in a recess or even on the ground in a remote area if overhung by a rock for shelter. It is a typical crow nest with 4-5 eggs usually laid.

Voice[edit]

The voice is very varied, and many types of call are made, but the most common are usually described as a high pitched "caw" and the sound of a cork coming out of a bottle. A "wok-wok-wok" is given by a bird in flight if straggling behind the group, and various clicks and mechanical sounding rattles are also heard.

References[edit]

  1. ^ BirdLife International (2012). "Corvus caurinus". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013. 
  2. ^ a b American Ornithologists' Union. (1983) Check-list of North American Birds. 7th Edition.
  3. ^ a b c d e f Pyle, Peter. (1997). Identification Guide to North American Birds
  4. ^ National Geographic Society. 1983. Field Guide to the birds of North America.
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Names and Taxonomy

Taxonomy

Comments: Considered conspecific with and constitutes a superspecies with C. BRACHYRHYNCHOS (AOU 1998).

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