Crows and Ravens
Wildlife Note
Printable Crows and Ravens Wildlife Note (PDF)
Crows and ravens belong to the large family Corvidae, along with more than 200 other species including jays, nutcrackers and magpies. These less-than-melodious birds, you may be surprised to learn, are classified as songbirds.
American Crow
Crows are some of the most conspicuous and best known of all birds. They are intelligent, wary and adapt well to human activity. As with most other wildlife species, crows are considered to have “good” points and “bad” ones— value judgements made strictly by humans. They are found in all 50 states and parts of Canada and Mexico.
Biology
Also known as the common crow, an adult American crow weighs about 20 ounces. Its body length is 15 to 18 inches and its wings span up to three feet. Both males and females are black from their beaks to the tips of their tails. Their feathers are iridescent, flashing highlights of blue, green and purple. Albinism occurs, producing pure or partial white coloration. The scientific species name
brachyrhynchos means “short beak.” A crow’s beak is actually sturdy and quite large at about 2 ½ inches long. However, its beak is short compared to that of the closely-related raven.
Crows are found in Pennsylvania year-round. This does not mean the same individual birds remain in the state all the time. Crows are “partial migrants” which means that some stay the winter where they nest while some migrate south and others wander locally to forage and roost with other crows. Young crows are more likely to migrate while older crows tend to stay on their territory all year around. Some crows that breed in Pennsylvania migrate south starting in late September or early October and are replaced by birds from the north. Northern migrants remain in Pennsylvania over winter while some crows hatched in Pennsylvania fly as far south as the Gulf of Mexico.
Flocks of crows range widely for food. They can travel up to 30 miles a day in search of food in the winter. Foods include grasshoppers, caterpillars, grubs, worms, most insects, grain, fruit, the eggs and young of other birds, organic garbage and just about anything that they can find or overpower. Crows also feed on the carcasses of winter – and road-killed animals.
Crows have extremely keen senses of sight and hearing. They are wary and usually post sentries while they feed. Sentry birds watch for danger, ready to alert the feeding birds with a sharp alarm caw. Once aloft, crows fly at 25 to 30 mph. If a strong tail wind is present, they can hit 60 mph. These skillful fliers have a large repertoire of moves designed to throw off airborne predators.
Crows are relatively gregarious. Throughout most of the year, they flock in groups ranging from family units to several hundred birds. During winter, crows may gather by the tens of thousands in areas where food is plentiful. Later, these flocks break up as nesting season approaches.
Males vie for mates through fighting and spectacular flight routines. Once paired, the male and female search out a secluded woodlot to raise their brood. Both sexes share nest-building and egg-incubating duties. There is evidence that crows pair for multiple years and some mate for life.
A nest site is usually chosen away from those of other crows. Most often, nests are built in the crotch of a tree, 10 to 70 feet above ground, usually more than 25 feet. A typical crow’s nest is a large, substantial basket, 22 to 26 inches across, built of twigs, sticks, bark and vines. The deep central cup is lined with moss, shredded bark, grass, deer hair, fur, feathers or similar material.
After mating, the female lays 3 to 8 eggs (usually 4 to 6) in April and May. Eggs are oval, bluish-green, and blotched and spotted with brown and gray. The young hatch following an 18-day incubation period. Ten days after they hatch, the young crows are almost fully feathered, and their eyes are open. They leave the nest at five weeks of age and look like small adults. Young birds follow, imitate and learn from their parents all summer. Many times, the family group sticks together until the following spring. Young crows from the previous year’s nest often assist their parents with rearing the young and defending the territory.
Crows are both predators and prey. As predators, they rob nests of songbirds and waterfowl, killing and eating newly hatched young, or cracking eggs. As prey, young crows and unhatched crow eggs are eaten by raccoons, opossums, and tree-climbing snakes. Hawks and owls kill nestling, fledgling, and adult crows. Crows are especially vulnerable to night attacks by great horned owls.
If crows locate an owl during the day, they will mob it—swooping low, calling excitedly and attracting other crows, and generally harassing the bigger, less-maneuverable bird. They also mob hawks. In turn, crows are mobbed by smaller birds, especially kingbirds and red-winged blackbirds.
Crows are curious. Shiny objects fascinate them, and they have been known to fly off with bits of glass, rings, keys, etc. Crows exhibit their intelligence by imitating many sounds, including whistles, cats, machines and the human voice. Crows have a good vocabulary—a wide range of caws, crowing noises, coos, and other soft, melodious sounds they use to communicate with each other.
Population
Crows not only live alongside humans, they have survived in spite of them. Because of their habits of pulling up corn shoots and occasionally robbing game bird nests, crows have been persecuted. Today, however, humans also recognize that crows can be beneficial in helping to control harmful insects such as tent caterpillars, locusts and white grubs, in cleaning up dead road-killed birds and animals, and even in removing improperly disposed garbage.
Some estimates put the crow population at more than 30 million in North America. Their numbers may be affected by man-made substances such as aldrin, dieldrin, heptachlor and DDT that have been introduced into the environment (All are now banned). When these insecticides accumulate they cause local reproductive failure or thin eggshells in some bird species. However, it is speculative whether this is the case with crows. Crows and other members of Corvidae are particularly susceptible to West Nile Virus. Populations have declined since that disease has entered the country. This seems especially true in urban areas, but they are still common enough that the declines are not perceived by the casual observer.
Each year, many crows winter in southern Pennsylvania, where weather conditions are relatively mild, and food is abundant. Here, they may group into flocks of thousands that congregate nightly at roosts—spots where crows have sometimes gathered together for decades. Each day, crows fly in different directions from the roosts, then feed and return at night. Most birds leave and return along the same route each day.
The crow is classified by the federal government as a migratory nongame bird. It’s the only bird in this classification that may be hunted. In Hawaii, however, crows are protected because there is an endangered crow species there. Crows may be hunted during established seasons which may not exceed 124 days per year. States are prohibited from establishing seasons during the peak nesting period. Individual states set season dates and regulate hunting methods, bag limits, etc., under regulations set by the U.S. Fish and Wildlife Service.
Habitat
Corvus ossifragus, which means “bone breaker,” never strays too far from the Atlantic and Gulf coasts and tributary rivers. In Pennsylvania, the fish crow inhabits riverine habitats and agricultural landscapes. Its Pennsylvania distribution centers in the southeast and along the Susquehanna River, including the West Branch to Clearfield County and up the Susquehanna’s North Branch to the New York state line. Some fish crows now occur commonly in the Juniata River drainage and spottily in the Ohio River drainage as far west as Butler County. Where the fish crow occurs, it is fairly common, but it is sometimes confused with the American crow. If the two are seen together, the fish crow can be distinguished by its slightly smaller overall size, shorter legs, and smaller bill. The best identifier is its call, a short, nasal car or
cah-cuh, as opposed to the distinct caw of the American crow. (A young American crow, however, may sound like a fish crow, so it is difficult to distinguish the two species in late spring and summer.)
As its name implies, this bird feeds on fish. However, it also eats a variety of other foods. Along the shore, it captures fish and small crabs, sometimes steals food from the smaller gulls and terns, and scavenges for whatever it can find. Inland, the fish and common crows often feed together, frequently in agricultural fields. Other songbirds’ eggs and nestlings occasionally fall prey to the fish crow.
Nest and eggs are very similar to, though a bit smaller than, those of the common crow. Like their cousins, fish crows build their nest in trees.
Common Raven
The common raven,
Corvus corax, is a less common Pennsylvania resident than the American crow, but is found in a wide variety of habitats especially the deep woods. Formerly they were found mainly in the mountainous northcentral region especially the Seven Mountains and Endless Mountains regions. They have returned to the common status that they had in the 18th and 19th centuries. Their numbers declined so much that by the late 19th century, some considered it to be possibly extirpated from Pennsylvania. Today, the raven population is recovering and expanding into many counties including agricultural areas. Ravens are abundant in Canada and the Rocky Mountains. Favored habitat is remote, heavily-forested wilderness, seacoasts and wooded islands.
Ravens are 20 to 25 inches in length, with a wingspread of about four feet. Their plumage is entirely black, with green and purple iridescence. Both sexes are colored alike; males are generally larger than females.
The raven is often confused with its close relative, the crow, but there are major differences between the two species that are especially apparent when crows and ravens are seen together. Common ravens are much larger than American crows, over double their one-pound size. They are about the size of a red-tailed hawk. Ravens are built for soaring and gliding with long, narrow wings and a broad wedge-shaped tail. Ravens also have a shaggy throat and a massive bill that allows them to tear into carcasses and kill small animals. Ravens eat rodents, insects, grain, fruit, bird eggs and refuse. They consume much carrion, especially in winter. In northern Pennsylvania, they are often seen along roads, where they feed on road-killed deer, raccoons, opossums, etc. Ravens also prey upon sick and injured animals.
A raven is every bit as alert as a crow and possesses sharp eyesight and hearing. Ravens are considered among the most intelligent of all birds. Like crows, they can learn to imitate a variety of sounds, including the human voice. In nature, their calls include guttural croaks, gurgling noises, and a sharp, metallic “tock.”
Ravens are skillful fliers. Their acrobatic courtship display flight is especially spectacular. After mating, a pair will seek out an isolated nesting spot, usually at least a mile away from any other ravens. Formerly they only nested on remote cliffs and large trees, but they are becoming more tolerant of people. Each year, more seem to be nesting in closer proximity to civilization and entering towns in winter to feed on litter and garbage. Some ravens now nest on large structures like transmission towers and football stadiums and forage in agricultural landscapes. Other ravens nest in deep woods where they rarely see humans. These, more typical nests are built on cliffs or near the tops of large trees. Of 17 raven nests found in a Pennsylvania study, 13 were on cliffs, three were in hemlocks (45 to 80 feet up), and one was 85 feet up in a white pine.
Ravens often build a new nest on top of the previous year’s nest. Nests are constructed of large sticks, twigs and grapevines. The outside diameter is 2 to 4 feet; inside diameter, one foot. The 6-inch deep central hollow is lined with deer hair, moss, shredded bark and grass.
The female lays 3 to 6 (usually 4 to 5) oval eggs, which are greenish and covered with brown or olive markings. Eggshells are rough and dull-looking. Incubation, which is mainly by the female, lasts about three weeks. Young are altricial. They leave the nest about one month after hatching. Ravens may live as long as 35 years in the wild, but much less is normal.