I was driving my truck along a country road about 70 miles east of Houston. A large flock of American robins flushed into the air as I drove past a hedgerow of yaupons. Glancing in my rearview mirror, I saw the flock return to the hedgerow as I moved down the road.

I turned my truck around and eased up along the roadside near the yaupons. I turned off the truck's engine and scanned the scene with my binoculars. Robins were everywhere, numbering at least 500 to 700 birds just in the few acres around me. They were perched in the surrounding tallow trees, standing in the grassy fields, and sitting on the tops of yaupons. Each yaupon hosted maybe 50 robins at a time.

A car whizzed along the road. The robins once again flew into the air and landed 200 feet away in the grassy field. Some of the birds perched in the rattle bean bush scattered throughout the field.

The well-known red on the breasts of these American robins was a bit duller than it is in the spring, having a rusty red hue that is far less conspicuous than in the spring. With grayish backs and dull red breasts, the robins blended in with the drab winter landscape. Of course, the robin's winter coat of feathers is a fresh coat. As the tips of the breast feathers abrade over the winter months, they will brighten into a shiny reddish-orange tint that will match the bright colors of spring.

I've always been fascinated by American robins assembling and moving around in large flocks during the winter. Winter flocking behavior may benefit robins in at least three ways. First, a large group of robins may be better able to locate scarce winter food sources. Second, robins grouped together can make it harder for a predator such as a hawk or a bobcat to single out a bird for attack. Third, a flock of robins roosting in a tree, huddled together, can stay warm on cold winter nights.

I watched as the robins regrouped around the yaupons and adjacent tallow trees, only to be spooked away by another passing car. Flocks of birds are wary of fast moving things like cars because hawks and bobcats move swiftly. It's therefore risky for robins to wait and see whether or not a fast moving object is a harmful predator or a harmless car.

Fortunately for the robins, the road by the yaupons saw only an occasional automobile. The birds were able to return to the bushes in relative peace. They moved in and out of the yaupons like a crowd of people going in and out of a fast food restaurant at lunchtime. Also, like people chomping on sandwiches, robins were chomping on fruit. The robins were eating yaupon berries. Typically, three or four robins at a time would perch on an outer branch of the yaupon and pick off the berries, often swallowing them whole. They'd then move to another branch and gobble up more berries. Other robins hopping along other branches of the same yaupon were gulping down more berries. Each yaupon in the hedgerow hosted dozens of robins so that nearly all the birds in the flock of robins had found a spot on a yaupon branch to feast on berries.

The yaupon (Ilex vomitoria) is an evergreen shrub or tree that's a common under story plant in the forests of East Texas. A member of the holly family (llex), it can also grow in clusters along fence lines or in brushy fields. In the spring, a yaupon produces tiny white flowers. But the yaupon's lustrous beauty comes in the fall when bright red berries decorate its branches.

Seven species of birds including mockingbirds, cedar waxwings, and American robins feed on yaupon berries. Raccoons and opossums munch on the berries, too. (We humans, however, shouldn't munch on the berries because they're poisonous to us.) Cold weather ripens yaupon berries, and the recent frost must have made the berries a tasty treat for the robins.

The robins were excreting seeds almost at the same rate they were ingesting the berries. The noise of seeds being excreted on the ground and the clucking call notes of the robins filled the air with a discordant but oddly pleasant sound.

Foraging flocks of birds have a variety of call notes such as clucks, chinks, or seeps. Anyone who has raised barnyard chickens knows these sounds. It's the way birds communicate with one another to signal a source of food, to maintain the unity of the flock, and to warn of danger. Research indicates that birds, like chickens, produce warning alarm calls at a higher frequency than the human ear can detect.

That may be why I didn't hear alarm calls from the robins when a red-tailed hawk landed on a power line pole across the street. Nonetheless, when the hawk swooped down on one of the yaupons, the robins had already flown off in unison to escape the hawk's talons. Had they signaled each other with an alarm call beyond my hearing range? That question is fodder for research.

The hawk flew off and the robins returned to their fruit eating frenzy at the yaupon bush. Soon, a flock of yellow-rumped warblers flew into the bush to feed on the insects stirred up by the robins. A foraging flock of one bird species will often attract a flock of another bird species. It's one way that birds find food. Are we humans so different when we flock to restaurants where other humans hang out?

I drove away slowly so as not to flush the robins. I had reviewed a lesson in ornithology and ecology by simply watching those rapacious robins. My experience was proof that an ordinary sight can serve as an extraordinary study of nature.

Gary Clark and Kathy Adams Clark - NPN 134

Gary Clark is a writer and associate dean of natural sciences at North Harris College in Houston, Texas. Kathy Adams Clark is a professional nature photographer. Learn more about them at www.kathyadamsclark.com.

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