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Home > Programs > Bureau of Natural Resources > Division of Fish & Wildlife > Crows, Ravens and West Nile Virus
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Crow and Raven Fact Sheet

Introduction

Due to the 1999 outbreak of West Nile Virus (WNV) in New York, Connecticut, New Jersey, and Maryland the Rhode Island Departments of Health and Environmental Management have begun a statewide action plan to address concerns with the virus becoming present in Rhode Island. One aspect of this plan is surveillance by the Department of Environmental Management (DEM) of bird species that have been or could potentially be affected by the virus. In particular, American crows will be monitored due to the high mortality rates exhibited by crows infected with WNV. At this early stage of the surveillance program it is uncertain how important American crows are in the perpetuation and transmission of WNV, however, due to their apparently high susceptibility to the disease crow deaths will serve as an excellent sentinel for the presence of the WNV in Rhode Island. DEM is also monitoring fish crows and common ravens due to their similar life histories.

As part of the awareness program DEM has prepared this informational pamphlet about crow and raven life histories. The pamphlet also contains information on how to identify infected birds, and informational links to where residents can find more information about crows, ravens, mosquitoes, WNV and other mosquito-borne diseases.

American Crow (Corvus brachyrhynchos)

The American crow is one of the most recognizable birds of Rhode Island, weighing approximately 20 ounces with a body length of 15-18 inches. Both sexes are similar in size, however, females are slightly smaller. Their primary coloration is black with iridescent highlights of blue, green and purple.

Crows are considered migratory, however, in more temperate states such as Rhode Island they remain year round. Migratory behavior in Rhode Island is likely to be limited to only daily movements between habitats in search of food. These movements can range up to 50 miles.

Crow habitat usually consists of interior and edges of open deciduous, coniferous and mixed forest. However, they often prefer woodland sites that are adjacent to agricultural lands. In winter months crows will often congregate in coastal area habitat where food can be easily accessed. Crows are considered omnivorous feeders eating food items such as insects, worms, grain, fruit, bird eggs, young of other birds, garbage and carrion.

Crows are a gregarious species flocking in numbers ranging from relatively small family groups to several thousand birds. Large groups of crows will congregate or roost primarily in fall and winter months with numbers decreasing as mate pairing and the breeding season approaches. When mate pairing is complete the paired birds will share nest-building duties, usually building nests in the crotch of a large tree 10-70 feet above the ground within secluded woodlands. Nests are 22-26 inches across and are built primarily of woody materials. Eggs are laid from late March through mid June, with clutch sizes ranging from 3-8 eggs with an incubation period of 18 days. Both the male and female crows share in the incubation duties. After the eggs hatch there is a nestling period of 25 days. It will then take 2 years for the new hatchlings to reach sexual maturity.

Fish Crow (Corvus ossifragus)

The fish crow is a relatively uncommon species in Rhode Island and when observed is likely to be mistaken for an American crow. This is due to their similar life histories and morphological features. The major differences between the two species are their range and calls. Fish crows tend to be a coastal species that spends much of its time along the Atlantic and Gulf coast from southern New England to Florida. However, it is not unlikely for them to be observed inland feeding and roosting along side large flocks of American crows. The best way to identify fish crows is by their short nasal calls car or cuh-cuh as opposed to the caw of the American crow. However, juvenile American crows do have a similar sounding call in late spring and summer.

Fish crows are similar to the American crow in coloration, body weight and length. The diet of fish crows is also similar but with a higher intake of aquatic organisms. This is due to their preferred feeding habitat of tidal flats, beaches, rookeries, and brackish waterways.

The breeding and wintering habitat of fish crows consists of wooded marine shorelines, coastal marshes and inland wetlands along tidal rivers.

Nesting behavior of fish crows are also similar to American crows, however, they do nest higher at approximately 20-80 feet above the ground and build slightly smaller nests.

Common Raven (Corvus corax)

The raven is another species uncommon to Rhode Island and is also often mistaken for an American crow, even though the raven is much larger with a body length of 21.5-26.5 inches and a wingspan of up to 4 feet. Despite being uncommon and difficult to differentiate they are occasionally seen in Rhode Island. Their normal range in the northeast consists of the mountainous regions of Maine, New Hampshire and Vermont and they are also abundant in Canada and the Rocky Mountains.

The raven's preferred habitat is heavily forested wilderness, seacoasts, and wooded islands. Feeding habitat is similar to crows and like crows, ravens are also omnivorous, however, road-killed carrion such as deer, raccoons and opossums are a major food source.

Nesting habitat consists of cliffs and tall trees. Nests are usually built 45-85 feet from the ground and are constructed of the same materials as crow nests and range in size from 2-4 feet in diameter. Other nesting behaviors are similar to those of American and fish crows, however, the nestling period and age of sexually maturity is longer. The nestling period for ravens is approximately 40 days with sexual maturity being reached after 3 or more years.

Crows and West Nile Virus

Crows can not transmit the West Nile Virus to humans. Transmission comes from the bite of infected mosquitoes. Crows must first become infected from the bite of an infected mosquito, primarily (Culex) species. After being infected crows can then infect other mosquitoes that bite them which could subsequently bite and infect humans. However, WNV is a newly emerging disease in the northeast and it is not recommended that any untrained persons handle potentially infected birds. In the event that a crow must be handled it is recommended that gloves be worn.

If a dead or infected crow is found in a particular area it does not necessarily indicate there are infected mosquitoes in that area. Crows have the ability to travel long distances from areas that may actually contain the infected mosquitoes. Furthermore, a majority of crows found and tested for WNV do not have the virus. Infected live crows will often appear sick exhibiting neurological symptoms such as head tilt, paralysis and staggering, usually showing no signs of injury (i.e., bleeding, wounds or fractures). Dead or dying crows may also have fecal feather staining and/or appear emaciated.

If you encounter a crow die-off that you suspect is a result of WNV please contact DEM Mosquito Abatement at 788-3698.

Literature:

Crows of the World, by D. Goodwin 1976
Rhode Island Department of Environmental Management Fact Sheets:
West Nile Virus
West Nile Virus Bird Submission Information and Precautions for Horses and Horse Owners

Internet Links:

Rhode Island Department of Health

Rhode Island DEM West Nile Virus and EEE Index Page

Centers for Disease Control and Prevention (CDC)

(CDC) answers your questions about West Nile Encephalitis

United States Geological Survey (USGS) Fact Sheet on West Nile Virus<

USGS National Wildlife Health Center

Informational Acknowledgments and References

Bureau of Information and Education, Pennsylvania Game Commission
Connecticut Department of Environmental Protection
Centers for Disease Control and Prevention
New England Wildlife: Habitat, Natural History and Distribution, Richard M. DegGraaf and Deborah D. Rudis, 1986.
A Field Guide to the Birds, Eastern Land and Water Birds, Roger Tory Peterson

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