Harassing Predators

 

(This 887th Buffalo Sunday News column was first published on March 23, 2008.)

 

File written by Adobe Photoshop® 4.0

Eastern Kingbird harassing a Red-tailed Hawk

photo by Glenn Clark

 

Anyone who spends time outdoors has probably seen examples of what can only be termed reckless behavior. A soaring or perched hawk harassed by a kingbird or robin. Chickadees, nuthatches, titmice and kinglets mobbing a screech-owl. A clamorous flock of crows chasing a great horned owl. Common terns dive bombing a great black-backed gull approaching their colony.

 

That kingbird or those terns will even attack us if we approach their nests.

 

Bird watchers take advantage of small birds' interest in picking on an owl in daytime. They whistle or play a recording of a screech-owl's whinnying call to attract these so-called dickey birds. Often a dozen or two of the little birds approach to join the action.

 

Most owls are at a particular disadvantage in daytime. (The daytime hunting hawk owl is one exception.) The eyes of our more common owls are designed for night vision and daytime finds them blinking or with their eyes shut. Having completed their night shift, they seek only to sleep through the day.

 

Other big birds, especially when flying, are at a different kind of disadvantage. They are like ponderous World War II bombers attacked by Japanese Zeros, German Messerschmitts, British Spitfires or our own Wildcats and Thunderbolts.

 

Like those fighter planes the smaller bird has greater aerodynamic control and can attack from above or behind. It may even light on the larger bird's back to deliver painful pecks. The hawk's common defense is usually to leave the area. It responds to those pecks by briefly folding its wings and dropping a few feet.

 

Why do birds do this? Not enjoying special insight into avian minds, I only conjecture by comparison with our own responses. First, of course, is defense of their nest. A better response might well be to keep quiet and let natural camouflage do its work, but give the birds credit for their concern.

 

More likely, I think that the source of this behavior is simply testosterone-driven showing off. Look at me, the daredevil. I can take on these ogres many times my size.

 

The larger birds are not, however, entirely defenseless. USA Today science columnist, April Holladay, recently answered this reader inquiry: "How come big birds don't take a whack at little birds harassing them?" Her answer is that they do occasionally turn on their tormentors and the result is usually very serious.

 

Maurice Braun, former director of Hawk Mountain in Pennsylvania, told this story: "Lying on my back and scanning the zenith, I picked up a small hawk making frequent passes at a much larger, dark bird, annoying its fellow traveler. The dark bird proved to be an adult golden eagle. It made a sudden thrust forward, executed an Immelmann turn [that's a fighter pilot maneuver] as effortlessly as a fly landing on a ceiling, and then, to my amazement, it seized the smaller hawk, which seemed to put up a momentary, hopeless struggle. Down came the two birds precipitously, the eagle with set wings and clutching its victim. As the eagle plunged to earth, the wings of the smaller bird were fully outstretched, and I glimpsed the ruddy breast of the red-shouldered hawk.  The eagle, still clutching its prey, disappeared into the densely wooded flank of the ridge."

 

Bruce Ostrow told of another event: "I noticed a red-tailed hawk and an American crow fly out of the trees. The crow was chasing the hawk and repeatedly attacking the hawk's tail from above. When the hawk and crow approached it, an eagle flew directly at the pair. The hawk dived out of the way, but the crow did not have time to evade the eagle. The eagle grabbed the crow head-on with its talons, killing it instantly."

 

These episodes were rare enough to warrant reports in ornithological journals. Yet European ornithologist Eberhard Curio reported 35 cases of predators turning on harassers.

 

Why are these predator responses to these attacks so few in number? Holladay's answer: the predator normally does not strike mobbers because maneuvering mid air costs energy, and does not benefit it sufficiently."

 

We usually think of the big bird as the playground bully and to root for its smaller attacker, but nature does not show our kind of favoritism.-- Gerry Rising