Birds of a feather often kill together Two eagles too much for one wily fox

January 20, 1993|By William K. Stevens | William K. Stevens,New York Times News Service

The majestic image of the lone eagle may often hold true. But scientists are also beginning to piece together a more complex picture of eagles, hawks and falcons as team players whose hunting tactics and cunning intelligence invite comparison with the wolf and the fox.

Eagles, in fact, not only mount concerted and successful attacks on the fox itself; they also deceive monkeys, humans' close relatives, in the deadly game of predator versus prey. By acting together, they are even able to bring down big animals like deer, antelopes and African bushbucks.

Diving, swooping and executing barrel rolls, peregrine falcons double-team rapidly darting swifts, which are birds that no single falcon could possibly outmaneuver. As the swift veers right and left in a horizontal plane, both male and female falcon come at it from above. The male, smaller and more agile, reverses course once it is below the swift and attacks a second time, from beneath. The multiple assaults drive swifts to such distraction that they fly into obstructions or plunge into water, becoming easy pickings.

And in the Southwest, family groups of Harris' hawks assemble each winter morning, divide into platoons and scour the countryside for rabbits. When one is found, the platoons converge and go on the attack. If necessary, one platoon flushes the prey from brush directly into the talons of the other. If a speedy jack rabbit leads them on a chase, the hawks pursue in relays that keep the quarry running till it drops.

These hawks are "not one whit behind a wolf pack" in their hunting behavior, said Dr. David H. Ellis, an animal behaviorist and raptor expert at the Patuxent Wildlife Research Center of the U.S. Fish and Wildlife Service at Laurel, Md.

As the grimly fascinating evidence accumulates, it is forcing scientists to reassess their longstanding treatment of raptors as solitary predators. Often the birds do hunt alone, and the difficulty of observing them at work has made it hard to discover other kinds of hunting behavior.

But now, according to a study in the current issue of the journal BioScience, there are enough observations to suggest that eagles and their cousins command a wide repertory of predatory actions, including the most sophisticated. This command may be essential to the species' long-term evolutionary survival strategy.

Raptors' newly appreciated prowess reveals "a high degree of intelligence," said Dr. Ellis, the primary author of the paper in BioScience. The other authors are Dr. James C. Bednarz, a behavioral ecologist at Boise State University in Idaho; Dr. Dwight G. Smith, a vertebrate ecologist at Southern Connecticut State University; and Dr. Stephen P. Flemming, an ecologist in Sackville, New Brunswick.

Just how bright raptors are relative to the intelligent mammals they kill is unclear and a subject of future research. But in any case, the catalog of behavior culled by Dr. Ellis and his colleagues from the scientific literature adds up to a chilling picture of raptor craftiness.

Some hunting hawks travel with similar birds, like vultures, to disguise their presence from the prey. A number of raptors follow the leading edges of fires, rising flood waters, moving trains and even people to capture prey flushed by the disturbances. Peregrine falcons have accompanied a moving train for up to six miles for this purpose.

Gyrfalcons in Alaska often followed a trapper to catch ptarmigans, birds that he flushed while tending his traps. In an extreme example, a northern harrier prowled an active bombing range to nab animals and birds scattered by the exploding bombs.

In Venezuela, Dr. Ellis observed a white hawk traveling with a troop of monkeys acting as de facto "beaters," much as humans beat game to the hunters.

Some species, like ospreys, learn of food sources from their flock mates in the colonies where they live, and all the ospreys then go search for prey. And golden eagles in the American West have been known to pounce in semicoordinated attacks on mule deer and antelope, killing them in the winter snow.

But none of this behavior constitutes true cooperative hunting. As used by Dr. Ellis and his colleagues, the term requires that the foraging pair or group be a stable social unit; that some members, in a division of labor, sacrifice their own prospects for a direct kill in deference to the group interest; and that group members share in the spoils.

In the most complex forms, raptors exchange signals to coordinate the hunt and cooperate in hunting outside the breeding season. Many instances suggesting this level of behavior have been observed.

In Manitoba, an adult and a juvenile golden eagle were observed attacking a fox in team fashion: the juvenile, from a height of about 25 yards, dive-bombed the fox from behind, making loud cries to attract the fox's attention.

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