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Tuesday 20 March 2012

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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

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