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If youíre a Cowbird, old habits die hard

Bill Meredith

"Black and white buffalo pass in and out of red barnsÖ."
Aldo Leopold, A Sand County Almanac, 1949

(February, 2015) I looked out of the kitchen window one morning last month and was not surprised to see that half of the yard was white. That was not unexpected; after all, it was January, and snow had been forecast. However, I was surprised to see that the rest of the yard was black, and seemed to be moving, like the raisins used to do when my grandmother poured them into a pan of boiling rice on her old coal stove. It was confusing, but after a moment rational thought took over, and I realized that if I would blink my eyes a few times and get fully awake, normality might return. I tried it, and the raisins turned into cowbirds. I had not seen any of them since last summer, but here they wereÖ hordes of them under the feeder and in the adjacent trees.

It takes a while to absorb something like that when youíve just got up. The first explanation that came to mind was that Alfred Hitchcock was alive and well and living in Emmitsburg; but old habits soon took over. Ecologists always start counting things when suddenly confronted with the unforeseen, so I began calculating. I picked several areas of about a square yard and counted the cowbirds in each of them; they averaged about 11 or 12 birds each. Estimating that the area I could see through the window was about five yards on a side, that would make it 25 square yards. I didnít have pencil and paper handy, so I rounded the observed 11 or 12 down to 10, which I could multiply in my head, and added 100 more to account for ones in the trees and the fudging of the numbers. That gave me a minimum estimate of 350 birds. Looking at the entire mob of them, that didnít seem unreasonable.

Watching the swarming mass seemed to make my mind dizzy, and it wandered off into the past. When the first European settlers arrived in this area, about 300 years ago, there were no cowbirds to be seen. This region was forested back then, and cowbirds are adapted to grasslands, not forests. They originated in the prairies of the Midwest, where their ancestors made a living by following herds of ancestral buffalo from time immemorial, even before the last Ice Age.

In those days the buffalo numbered in the millions, and like the wildebeests in Africa, they were constantly on the move; if they had stayed in one place, they would have eaten every sprout of green vegetation within reach. Their migration pattern took them northwest from Texas and Oklahoma to the edge of the mountains, then to Wyoming, the Dakotas, and then southward again. Cowbirds travelled with the herds, and they too were in numbers beyond imagination; each tribe of Plains Indians had a name for them in its language which translated to "buffalo bird" in English.

In spring and summer they ate insects, which were flushed up from the grass by buffalo; in winter, they ate seeds which they picked up from the ground or from buffalo dung. Because they had to move with their food source, they could not build nests and raise fledglings like other birds, so they evolved the habit that ecologists call nest parasitism; they laid their eggs in the nests of other birds.

Of course the coming of European settlers changed all that. In the east, forests were cut down and converted to farms, with fields of hay and various grains; so in an ecological sense, the eastern forests became interspersed with grasslands. In the west, the open prairie was fenced off, plowed, and planted, mainly with wheat. The great herds of buffalo were virtually wiped out in the 19th Century by hunting for their skins and meat, by farmers protecting their crops and fences, and by "sport shooting" by passengers on the railroads. Aldo Leopold, one of the most eloquent of the conservationists who succeeded Teddy Roosevelt, was old enough to remember the last of the buffalo herds, and he described the changing ecosystem of the prairies as populated by "black and white buffalo which moved in and out of red barns" instead of following the ancient migration route.

The cowbirds adapted. They still wandered about in flocks, but they patronized herds of cattle in the summer, and in winter they shifted from buffalo chips to cow pies. And many of them drifted eastward to the newly created "prairies" where the forests once had been. Here, they continued the old habits of traveling in flocks, feeding on insects in summer and seeds in winter; and they continued to practice nest parasitism, which we all learned about in school. They merge into larger flocks in the fall, and usually stay out in the countryside, where they wander from one dairy farm, feedlot, or grain field to the next.

Living in a flock is safer for them; there are more eyes to spot predators, so the individual birds can give more of their attention to finding seeds to eat. If one bird detects danger, there is no vocal signal; it simply takes wing, and the whole flock instantly follows. If a really big storm occurs, the flocks will move further south, but after a light snow they simply expand their search for new spots in the local area, often ending up in towns where they can find both food and shelter. When they find a place like my yard, and see other small birds around a feeder, they descend on it like the plague.

Watching them from a window where they are only a few feet away gives you a different view than the one you get from walking in a field. I noticed that they required less "personal space" than other birds; they were often only an inch or two apart, yet they made no attempt to peck each other like starlings or sparrows do. Flocking behavior apparently requires tolerance. I also noticed that while most of them were vigorous and well-groomed, there were a significant number that were less active and showed signs of ill health. Damaged legs, un-preened feathers, and improperly folded wings indicated that some of them would be at greater risk when a hawk came by and the whole flock took flight. This surprised me at first, but then I remembered the basic rule of population dynamics. To have a stable population size, the death rate must equal the birth rate. If each of the females lays ten eggs in the course of a summer, an equal number of deaths must occur to prevent the population from expanding to the point that it would begin to destroy the other species of small birds that become foster parents to parasitic cowbird babiesÖ and ecologists have found that the populations of various warblers and sparrows do decline when cowbirds become too numerous. Cowbirds can live at least 16 years in captivity, but in nature their life expectancy is much less. I would guess that all of the hundreds that stopped in my yard, only a handful will survive five years, and none will still be alive in ten years.

The snow melted after a few days, and the flock went back to the country. Yesterday it began snowing again around 10:00 A. M., and by noon the yard was full of cowbirds again. I donít particularly like them; but I was glad they came, because as I watched them the quotation by Aldo Leopold came to mind. I used to assign chapters from his book for my ecology class to read, and regularly read it myself for pleasure; but since retiring, I hadnít opened it. So now it rests on the stand by my reading chair, and Iím finding that the prose has not suffered from my neglect. I wish I could have met him; but he died in 1948 while fighting a grass fire near his farm on his beloved prairie. I was in high school then, and had not yet heard of him; but he was to become a role model for me. And the cowbirds brought him back to me.

Read other articles by Bill Meredith