Bennet Miller is a volunteer with Friends of the Alameda Wildlife Refuge, a committee of the Golden Gate Audubon Society.
Murders in the Island City: Meet the American Crow
I once saw a young mother hurrying her stroller down the sidewalk while furtively watching a raucous swirl of dozens of crows overhead, who did seem to be following her. I assured her that they wouldn’t bother her, it was just several families socializing. I did not mention that a flock is called a murder of crows.
The adult American crow is between 16 to 21 inches in length, weighing between 11 and 22 ounces, with a wingspan between 33 and 39 inches. Males are usually a little larger than females. Like the color selection for Henry Ford’s Model T’s, the American Crow comes only in all black.
Crows belong to the corvidae family, along with ravens, jays, and magpies; more than 120 species of corvids are known. McGill University comparative psychologist Louis Lefebvre has a scale of bird intelligence that put parrots and corvids at the top, with ravens and crows among the smartest.
Jennifer Ackerman’s brilliant book The Genius of Birds discusses tool making in crows (shaping sticks to acquire food) and the possibility they grasp analogies in problem-solving. Crows will also delay gratification if they sense a reward might be worth the wait.
Ackerman writes that crows use weapons. A crow lobbed three pinecones at a scientist’s head as he approached its nest. In another instance, a Steller’s jay, tired of waiting for a leisurely dining crow at a feeding platform, attacked the crow with a sharp twig it had snapped from a free. When the crow lunged back, the jay dropped the twig. The crow picked it up, sharp end out, and jabbed back; the jay flew away with the armed crow in pursuit.
Crows are omnivores and have a wide diet including insects, fruit, grains, nuts, marine invertebrates, worms, amphibians, rodents, snakes, roadkill and leftovers. One birder reported a crow with an entire slice of pizza in its beak.
Crows build large nests of sticks, usually in trees, sometimes in big bushes, and can begin incubation in early April. Clutches may number three to nine, usually four to six eggs, which are bluish green to olive, spotted with gray or brown. Incubation is about 18 days, with the young fledging about 36 days after hatching.
Young crows will stay with their parents for several years and help raise subsequent generations. The young face predation by raccoons, snakes, ravens and domestic cats.
Genetically, crows can live long lives, up to 30 years in captivity. In the wild, adult lifespan is usually seven to 10 years, facing predation primarily from several species of raptors.
Crows are so vulnerable to West Nile virus they are considered a sentinel species, indicating presence of the virus. They cannot directly transmit the disease to humans.
Researchers have presented a crow with a line of nine small caps, hiding food under the first. The next time the crow was shown the caps, the food was hidden under the second cap. Next, the third, and so on. The crow learned to anticipate the subsequent hiding places for treats.
Crows give gifts. Biologist John Marzluff notes that crows frequently given food may offer trinkets to the feeding tray: bolts, buttons, earrings, even a rotting crab claw. (There’s generosity.) This reciprocity suggests they understand prior acts and anticipate future benefits.
Marzluff’s wonderful research indicates that crows not only recognize individual humans, they warn their compatriots when a bad dude arrives and pass that awareness on to future generations. After they saw a human capturing crows, subsequent generations, unborn at the time of the original trapping, would scold, dive-bomb and mob the dangerous crow-napper.
Crows have been observed sliding down snowy hillsides on their backs. Scientists may offer their explanations, such as removing parasites, but you and I know the real answer — crows just wanna have fun. So, the next time you see a black bird larger than a robin, watch to see what it does. And remember they contribute by eating insects and road kill.
To learn more about crows and other birds in Alameda, go on a Golden Gate Audubon Society field trip; listings are posted at www.goldengateaudubon.org.