| When hopelessly caught in the jaws of a hungry snake, some frogs emit a high-pitched "scream." Researchers puzzled over this phenomenon - after all, snakes can't hear, so screaming isn't going to deter them. Further study revealed that the frog's "scream" invariably attracts a neighborhood crow or two. The snake, disturbed by the sudden arrival of one of its own predators, almost always let the frog go in its haste to escape the crow. -DLS |
Photo © Greg Neise
by Barbara Rose
What a delicious sound! It is not merely crow calling to crow, for it speaks to me too. I am part of one great creature with him; if he has voice, I have ears . . . Ah, bless the Lord, O my soul, bless him for wildness, for crows that will not alight within gunshot!
Henry David Thoreau, Journal, July 11, 1855
For an issue of The Ark devoted to unusual defense mechanisms, what can one say about those raucous members of family Corvidae, crows and jays? Screeching noisily, they mob interlopers. Nothing unusual there. They sound like any ordinary gang of teenagers, the aldermen in city council, or, for us C-SPAN fans, the Democratic minority in the Senate.
Blue jays . . .
are just plain noisy. They are the first to spy an intruder in the woods and use their wide vocabulary to warn others. They mimic the cries of red-tailed and red-shouldered hawks, which they always harass. They like to be in the thick of the action when other birds are around. They will invade and hold an area in which food is found to eat nuts, corn, domestic and wild fruit, insects, carrion, and baby birds.
Jays will hide far more acorns than they can possibly consume over the winter season. This behavior may discourage intruders by removing excess food from their territories. It perpetuates oak trees, too. Captive jays will tear newspapers from the floor of their cages to use as tools to retrieve food pellets that have fallen out of the cage.
At home in woodlands, they are rarely spotted in Chicago, although long-time birder and LPZ docent Doug Anderson counted a possibly nesting pair this year at the Paul H. Douglas Nature Sanctuary. It would be a first in many years. The suburbs and forest preserves are home to many.
In fact, blue jay populations have declined sharply in this century. In the past, they relied on stored acorns in winter. Pesticides and the reductions of woodlands and oak trees have taken their toll.
Jays are partially migratory, breeding in the north, then going south to mingle with nonmigrating southern jays. Flocks of up to a hundred birds can be seen in autumn skies.
Crows . . .
on the other hand, are easily seen in winter. Big, black, gregarious birds, they feed in open areas and nest and roost in wooded ones, so Chicago parks like Lincoln Park and Wooded Isle (as the Douglas sanctuary has been called since 1893 when it was built for the Exposition) are perfect habitat.
Crows are extremely aggressive toward hawks, great horned owls (their main predator, after humans), and other birds of prey. They quickly communicate the presence of a raptor in the area to other crows, who, as if by magic, flock together to harass the intruder until it leaves the territory. For example, on the Wooded Isle, there are usually three or four pairs of nesting crows. But when a red-tailed hawk lands there, according to Anderson, 30 or 40 crows will suddenly appear, screaming raucously, and chase it away.
Anderson related this story: Last year, a pair of Cooper's hawks nested on the island. It was the first time since 1904 that this formerly endangered species was known to nest in Chicago. Birders were anxious about the resident crows. Would they harry the hawks away? The crows, however, stayed very quiet throughout the nesting season and the long summer until the migratory hawks and their three fledglings left in the fall.
Why this unusual behavior? Anderson believes it was purely defensive. Cooper's hawks are outstanding hunters of other birds and have large appetites. In fact, the songbird population decreased noticeably during their stay on the island. Cooper's hawks can eat up to 12 birds a day. Even the chicks, after their third week, can eat that many robins, sparrows, and other small- to medium-sized birds. Anderson saw the young hawks chase crows. but the usually noisy corvids did not call in the troops. By lying low and hiding out, they were undoubtedly protecting their own nestlings (and themselves) from the expert avian predators.
Crows do not like competition, either. Introduced monk parakeets have visited Wooded Isle and even established a nest. They were so persistently pursued by the crows, however, that they gave up further attempts to nest. The parakeets have not been back.
So what is everyday life like for Chicago crows? Anderson says it is easy to spot their nests, which are large, twiggy, elongated, and placed high up. The incredibly versatile and intelligent crows make use of the many kinds of trees-willow, mulberry, cottonwoods-that are found in Chicago parks.
Like humans, they enjoy a pied-à-terre. City buildings will do. (So will odd construction materials. Peterson relates how a pair of Bombay crows made a nest of costly gold eyeglass frames that they stole from an open shop window). Crows are living atop the Hyde Park Coop Market on busy 55th Street. In fact, the proximity of the market is probably the appeal. Crows like our food and eat a lot of garbage.
Garbage may account for the fact that crow numbers are growing after a decline in the fifties and sixties. Birders report that numbers are up all over the country, according to Anderson.
Opportunistic omnivores, as are so many other wildlife species in urban jungles, crows eat carrion carcasses clean. So they are filling in for vultures, who do not usually visit Chicago proper. Small birds, eggs, and mice provide fresh protein. Mulberry trees provide delicious food as well as nest sites. Worms are abundant, especially after a rain, and crows strut about the lawns as they dine. Insects and seeds, especially grain, fill out their menu.
Both jays and crows hide food, even in captivity. They hide their stores on the ground, in holes, and on trees and buildings. They have been observed covering food by bringing stones from nearby to cover the cache.
Crows have been pursued with firearms, TNT, poisons, and traps. In fact, because of aggression toward them, they played a part in bird conservation. E. I. DuPont de Nemours organized crow-shooting contests at the end of World War I for no apparent purpose other than to sell its shells and gunpowder. The Audubon Society ended this practice by publicizing the contests, and grew to become a conservation giant.
Crows can be tamed and trained. One was kept by a naturalist at the Little Red Schoolhouse for years. Anderson said it delighted visitors by riding around on the shoulder and chatting like a parrot.
In addition to the common crow (Corvus brachyrhyncoc) and blue jay (Cyanocitta cristata), the Corvidae family includes magpies, rooks, jackdaws, and ravens. Ravens, once common, were extirpated in Chicago. They were known to nest here in 1855. By 1876, they were seen in winter only. The last Chicago sighting was 1953.
Many ornithologists, according to Peterson, put crows and jays at the top of the 60-million-year-old passerine (perching birds) family tree. They are intelligent, plastic, relatively unspecialized, and opportunistic. Higher mental faculties are most valuable to opportunists who take advantage of every opening. Like the wily coyote, crafty crows will be our neighbors for a long time.
Sources
Interview with Doug Anderson, 1995.
Bohlen, H. David. Birds of Illinois, 1989.
Robert Burton. Bird Behavior, 1985.
Gibbons and Strom, ed. Neighbors to the Birds, 1988.
Mlodinou, Steven. Chicago Area Birds, 1984.
Perrins and Middleton, ed. The Encyclopedia of Birds, 1985.
Peterson, Roger Tory. The Birds, 1963.
Peterson, Roger Tory. Field Guide to Eastern Birds, 1980.
