Monday December 10, 2012

In the Connecticut River watershed, if you drive on a roadway you have seen a crow eating carrion. What you are seeing is the modern American crow, scientific name Corvus brachyrhynchos, the "short-billed crow" descended from 20-million-year-old ancestors. The American crow is one of four species of crow in North America and occurs almost everywhere in the United States. Its range extends north to Hudson Bay. Crows do not migrate per se but there is some north-south variation between winter and summer ranges with breeding happening in the summer range.

The American crow is large, up to 21 inches long and weighing over a pound. Crow plumage appears black as do its bill, legs and feet. The crow has a fan-shaped tail, distinguishing it from the common raven's inverted wedge-shaped tail. Crows are omnivorous and eat just about anything including fruits, vegetables, insects, road kill, birdseed, small rodents, fish and other birds and their eggs. They communicate messages with their rude loud cawing including courtship, alarm, feeding, rally, comeback and fight. There are claims that in the wild crows can live up to 30 years.

Crows are social and unless in large roost groups called murders, live in family groups of up to 15 birds. Their natural enemies are the great horned owl and some hawks. Crows exhibit a cooperative defense behavior where they will mob a hawk until it leaves the area.


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When feeding, even having sent scouts in advance to the feeding area, crows place guards to sound warnings of danger. Why a group of crows is called a murder has been a mystery since the 15th century. One dictionary suggests "murder may allude to the crow's traditional association with violent death or to its harsh and raucous cry."

The crow's number one enemy is man because our negative feelings about crows extend from they are simply annoying to highly destructive, especially in agricultural areas. A recent new deadly threat to crows is West Nile virus. The virus, native to east Africa, arrived in New York City in 1999 spreading west and south across America. In the Northeast, a study found American crow populations decreased 31 percent since then. Despite the drop in numbers, the crow is still considered a Species of Least Concern.

During mating, crows are territorial. They build large nests of dead branches April to May, located in well hidden crotches high up in taller trees. Crows build new nests each year located close to the old nest sites. The outer structure measures up to two feet in diameter with a seven-inch diameter, five-inches deep interior of softer materials in which the eggs, once laid, are incubated and the young reared. Both male and female crows construct the nest, sometimes aided by one or more of their offspring from the previous two years.

Crows incubate a clutch of three to six eggs, 1.5 inch long, for 18 days. Even in the same nest, the eggs are of various colors from sky blue to camouflage brown with spots. The mother will brood the young birds for up to two weeks with the male and one or more prior offspring carrying food back to the nest. Somewhere between 30 and 40 days after hatching, the young want to leave the nest before they are able to fly. If they do not stay safely in the tree but fall to the ground, the crow family will continue to care for the young. If the fall does not kill them, predators do not eat them or helpful humans do not rescue them, they will rejoin their family.

Outside breeding season crows gather in large numbers at communal roost just before dark. This arrangement does not mean that individual crows are friendly with all other crows and they may fight for reasons such as defending territory, their nest, protecting their mate or breeding access to them, or defending some other resource like food. Crow family fights usually only involve a few pecks but fights between different families can be deadly. Violence toward a single crow could mean that it was injured, sick, or acting oddly because it might attract predators.

Crows are intelligent. They use tools such as shaping a stick and then sticking it into a hole in a fence post in search of food or breaking off pieces of pine cone to drop on tree climbers near their nest. Their intellect is captured in the Aesop fable depicting a thirsty crow faced with a pitcher half full with water, beyond the reach of its beak. After failing to push over the pitcher, it drops in pebbles, one by one, until the water rises to the top of the pitcher, allowing the crow to drink.

Crows remember the faces of threatening humans, scolding and bringing in others so they learn about the threatening person and spread the information about this individual throughout the crow community. Given that crows have long memories, people who hunt these birds, for example, could experience years of raucous harassment.

In spite of their discordant song, the crow is a truly exceptional member of the bird family here in the Connecticut River watershed.

David L. Deen, River Steward for the Connecticut River Watershed Council. CRWC is celebrating 60 years as a protector of the Connecticut River.