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04/19/09
Mob Attacks Eagles!
Filed under: General, Birding & Outdoors, Florida & SE US, Bald Eagle Nest
Posted by: Ken @ 6:14 pm

Several times, watchers at the urban nest of the Pembroke Pines (Florida) Bald Eagles saw Northern Mockingbirda and Common Grackles approach closely to adult and fledgling eagles, apparently trying to drive them off a favored roosting tree.

Smith, one of the veteran nest observers, captured this video of the action the day before yesterday:

I was shooting the scene next to Smith, and, a few times, saw a grackle actually pull at the adult eagle’s tail feathers. My shutter lag and my (much greater) reaction time made me miss photographing these close encounters, at least one of which appears on Smith’s video.

Here, a grackle makes a very close pass at the eagle’s head:

Grackle Attacks Adult 2-20090417

The adult keeps its eyes on the attacking blackbird, but actually seems passive and never strikes out at it:

Grackle Attacks Adult 20090417

Later, a grackle is poised to swoop down on Hope, the larger and older of the 13 week old eaglets:

Grackle Attacks Hope 2-20090417

The young eagle has suffered enough abuse at the hands of a small flock of Common Grackles, and flies away, but one grackle does not give up so easily:

Grackle Attacks Hope20090417

The eaglet flew directly over my head, so fast and low that I could hardly keep it in the camera’s viewfinder:

Eaglet Overhead 2-20090418

Why do small birds sometimes seem to put themselves at risk by harassing and even attacking much larger raptors? I have seen fragile little chickadees, titmice, and nuthatches join larger robins and jays to surround and scold a hapless Long-eared Owl or Red-tailed Hawk. Sometimes, mammals such as chipmunks and squirrels join the birds, calling excitedly and flicking their tails nervously.

Red-winged Blackbirds are known perch on the backs of larger hawks to pluck a few feathers as they drive them away from their nesting grounds. In my New Mexico back yard, I once watched several Mountain Chickadees and Bushtits join a group of jays and Clark’s Nutcrackers to take on a Merlin that was perched out in the open. The small falcon could have easily made a meal of even the larger birds, yet it merely held fast to its perch and appeared to be screaming back at the annoying assembly. Many of us have seen mockingbirds attack alley cats, actually striking them on their backs. (In Dallas, I saw a cat turn suddenly to catch and kill a mockingbird doing just this). In Alaska, I was mobbed by Arctic Terns when I approached too close to their nesting colony.

In an earlier Blog about mobbing behavior, I reflected on how crows often reliably led me to roosting hawks and Great Horned Owls, and once, to a Bald Eagle, and remembered that my weak imitation of a Western Screech-Owl caused a large number of smaller forest birds to cluster around my position, and remain for many minutes after I stopped calling. I wrote:

“We have noted that wild creatures tend not to waste energy—that their actions are usually purposeful, even if their meaning may not be immediately evident to us humans. “Mobbing,” the tendency of flocks of birds to approach certain predators is well known but the purpose of this behavior is open to speculation. Are the birds trying to drive the predator away? Are they simply alerting other birds to the danger?”

This interesting Wikipedia article goes into some detail about mobbing, and explores possible reason why an action that appears so risky may actually enhance the survival of prey species.

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