American Crow Diet & Hunting Techniques
One would be hard pressed to name all of the different types of food that American Crows consume. The diet of these omnivorous birds runs the gamut — small birds, bird eggs and nestlings, tadpoles, frogs and toads, snakes, turtles, small mammals, fish, insects, clams, nuts, fruits and carrion.
Crows use a number of techniques in obtaining their food. They find most of it as they’re walking on the ground, occasionally they probe just under its surface. You often see them lifting and flipping leaves, cow pies, sticks and small stones to see what creatures live beneath them. Crows have also been known to stand belly-deep in water as they hunt for fish. In addition, they sometimes hunt from a perch, pouncing on prey they see, and catch flying insects and small birds on the wing. Crows have even been observed using “tools” such as pieces of wood to probe for insects.
If their prey is large, crows will place it under one or both feet and tear pieces off with their bill (see pictured American Crow with road-killed Eastern Chipmunk it retrieved).
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American Crows Building Nests
Congratulations to Robyn Deveney and Chris Wings, the first Naturally Curious readers who accurately suggested the Mystery Photo depicted the tracks of an American Crow collecting nesting material. As I approached the pictured area, I flushed two black birds who were soon cawing and flying overhead, with a stick protruding from one of their beaks.
Crows are one of the earliest passerine, or perching, birds to engage in nest-building and egg-laying. Crows tend to build new nests each year, seldom reusing a nest from a previous year. In New England both members of a pair are busy collecting nesting material such as sticks, bark strips, weeds and mud, in March. They bring this material back to the nest site, which is typically a conifer, and construct a bulky nest usually in the crotch of the tree or on a horizontal branch. It takes anywhere from one to two weeks for crows to complete a nest and up to six days to lay 2 – 6 eggs. Incubation typically begins in early April.
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Sentinel Crows
Ornithologists have noted that especially during the winter, American Crows assign one or more of their flock to keep watch over the rest of the group, or “murder,” as they feed on the ground nearby. While acting as sentinels, the crows will call frequently, even when predators are not present. When they intensify their calling, the crows that are feeding often flush.
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American Crow Bills Used As Tools
American crows obtain most of their food on the ground as they walk along in search of seeds, insects, frogs, snakes, bird nests and small mammals. Their hunting techniques are varied and most involve the use of their bill. In search of invertebrates, crows will probe the soil with their bill, flick aside leaves, dig in the soil and even lift cow paddies. They fish for tadpoles and dig nearly an inch deep with their bill for clams. In winter, their foraging continues and as these tracks indicate, when the snow is only a few inches deep they will walk around and around in a given area, probing tufts of grass for hibernating insects, mice, voles, or any other form of life these opportunists find.
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Nictitating Membrane Provides Moisture & Protection to Eyes
You and I have two opaque eyelids, one above the eye and one beneath. When we blink, they meet in the middle of our eyes. Some birds, amphibians, reptiles, fish and mammals have three eyelids – two similar to ours, and a third translucent or transparent eyelid, called a nictitating membrane. This membrane moves horizontally across the eye from the inside corner to the outer edge of the eye, much like a windshield wiper, when needed for protection, to clear debris or to moisten the eye. Although this American Crow’s nictitating membrane looks as if it was blinding the crow, it isn’t. Because of the membrane’s translucency, the bird can still see when the membrane is covering its eye.
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Roosting Crows
After the breeding season, American crows begin to gather in small, communal roosts. By early to mid-winter the number of crows occupying a roost reaches its maximum. In the morning, shortly before and after daybreak, crows leave their nocturnal roosts in small groups and fly in all directions leading to feeding grounds. After having spent the day feeding, roughly two to three hours before sunset, small groups of crows gather in pre-roost sites, and from these fly along regular flight lines towards their roost. They are often joined by additional crows at pre-roost sites visited along the way. The closer the crows get to their final roost, the larger the group becomes. The same roosting sites may be used for many years and the number of birds in them varies from a few hundred to many thousands.
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