How Do We Find Out About Bird Biology?

Many of the essays in this book are loaded with "weasel" words -- birds appear to do this, or seem to behave in a certain manner, or may respond in a particular way for the following reason. Surely, one would think scientists could be more definitive about the biology of such a well-known group of animals. But they cannot.

One reason for the uncertainty is the difficulty of finding out what a rapidly flying animal does. Two White-throated Swifts that touch briefly in flight may appear to be copulating, but how (short of bringing them down for a biological assay) can we be sure? How can we even be sure that the two birds tumbling in midair as they sweep past us down a canyon at forty miles an hour are a male and a female? Finding answers in such cases may require detailed, logistically difficult, and time-consuming research involving such things as netting, trapping, examining and banding birds, photographing them with high-speed cameras, and often clever experimental alterations of the birds or their environments.

Suppose, after completing such a detailed study, a scientist is convinced that White-throated Swifts in one part of Arizona copulate in midair. How far can the researcher generalize such findings? Does it mean that White-throated Swifts everywhere copulate in midair? Do all other species of swifts copulate in midair? Ornithologists think all swifts are aerial maters. In fact, they assume that swifts are the only birds that do so on the wing. But they cannot be certain of either point. Maybe one obscure population of Palm Swifts in Asia actually mates only in their nests. And just possibly an Amazonian hummingbird, on occasion, copulates aerially above the canopy. That's why the authoritative Dictionary of Birds says, "Swifts are apparently unique in copulating in the air" (our emphasis). In short, statements by scientists are always provisional; they represent the best current evaluation of the situation, but are always subject to revision.

A related problem is that there are more than 9,700 species of birds, and, as we know, they are a rather diverse lot. Suppose, for instance, we wished to know whether female birds prefer males that hold superior territories. Just determining whether females of one species in one habitat have that preference is not a simple task. The territories of males must be mapped and criteria to judge territorial quality must be found. For example, to compare territories within a population of insect eaters an ecologist may be required to do many careful censuses of insect abundance during the breeding season, without disturbing the breeding birds. Finally, of course, the female choices must be evaluated, most likely by counting the number of nests and the number of young fledged within each male's territory, often a difficult task in itself.

So much for finding the answer for one species in one locality -- how about other localities? And, since male birds of most species are territorial, what about other species? Obviously, it would be a mistake to generalize from the behavior of one population living in one habitat to all species of birds in all habitats. It would be necessary to see if female choices were made not only in a variety of species, but also in different habitats. If this were done, a pattern should emerge slowly, and with it an opportunity to draw tentative conclusions. Further studies may tend to confirm or refute those initial conclusions, and after enough studies have been completed, a consensus will emerge. For instance, territoriality in most male birds is so well documented that it is treated as fact. That females tend to mate with the holders of the better territories is not so well established, but many ecologists think that it eventually will be.

Learning about bird communities can be even more difficult than drawing conclusions about the behavior of single species. Suppose, for example, we wished to know whether Downy and Hairy Woodpeckers were competing in three square miles of forest. One way to find out would be to remove all the Downy Woodpeckers in one square mile, all the Hairy Woodpeckers in another, and leave the third square mile undisturbed. Then comparing the fledging rates in the three localities should provide substantial information on the degree of competition. The logistics of doing such an experiment would be daunting, but more important, we and many others would consider its impact on the birds to raise serious ethical questions. Physical scientists generally ask whether the knowledge that might be gained from an experiment would justify the effort; biologists must also consider an experiment's effects on the organisms and natural systems being investigated.

In our essays we try to indicate how well established the conclusions are and, wherever possible, to describe the evidence on which they are based. The length of the treatments generally reflects how much is known about the birds, although the length of some of the most thoroughly studied species had to be shortened because of space constraints. You should be cautioned that there often appears to be more certainty in the data from poorly studied species; for instance, if only a few nests have been found, the range of heights above ground or clutch sizes will almost always be smaller than if hundreds of nests had been examined.

You may be disappointed by how little is known about so many aspects of avian ecology and behavior, even though many birds have been thoroughly studied. But looking at the bright side, that means that there are numerous opportunities for birder and ornithologist alike to add to the understanding of these fascinating creatures.

SEE: Territoriality; Polygyny.

Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye.