National Geographic : 1934 Jul
BLACKBIRDS AND ORIOLES* BY ARTHUR A. ALLEN Professor of Ornithology at Cornell University T WAS my first trip to the Tropics. As we stood on the newly finished dam, Colonel Gaillard was explaining the probable extent of Gatun Lake when water should finally be admitted to the Panama Canal. But my mind was on other things. I was an ornithologist craving bird ad venture, and while I listened to the Colonel with one ear, the other received most allur ing sounds from the undergrowth; and while my eyes took in the enormity of the dam I really perceived only strange shapes and bits of color flitting through the trees in the background. The next day, as I made my way alone to the beckoning forest, from the train win dow I glimpsed birds I had never seen be fore, and yet many of them had a strangely familiar appearance. There were hawks and swallows and woodpeckers in about the same numbers as one would see from a train window in eastern United States, but other groups flashed by in much greater variety. Instead of one species of humming bird, for ex ample, there were apparently four or five kinds, and the same was true of the brilliant tanagers. There were many more fly catchers, and there were birds of the oriole family (Icteridae) nearly as large as crows. A LESSON IN GEOGRAPHICAL DISTRIBUTION Still other groups of birds that one could never expect to see in the United States were much in evidence. Noisy little parra keets, for example, took the place of house sparrows, and gave the bird landscape an exotic appearance. In the forest I found warblers and vireos somewhat similar to those at home, but also many strange birds belonging to bird families I had never seen except in a museum or a zoological park. There were toucans with huge bills, and motmots with long racquet tails, and tree creepers, ant-thrushes, cotingas, and honey creepers that one never sees in the northern forest. Some groups of birds that are familiar companions in our New York and New Eng land woodlands, like the nuthatches and the chickadees, and the shrikes discussed in this article, had no counterpart in this trop ical jungle; and others, like the crows and jays and even the sparrows, were rare. Without realizing it, I was enjoying a lesson in geographical distribution that was to make clear to me, as never before, the origin of our North American bird life and the meaning of bird migration. Had I ven tured into a British woodland instead of a Panama forest, the birds might have ap peared equally strange to me; but even more striking than the number of new birds seen would have been the absence of rep resentatives of so many families that are found in North and South America. In Britain there would have been no humming birds, no tanagers, no flycatchers, as we know them; no wood warblers, and no blackbirds and orioles. On the other hand, there would have been more sparrows and buntings, more titmice, more crows and jays, more shrikes, and more of the birds belonging to the kinglet family. BLACKBIRDS AND ORIOLES CONFINED TO THE NEW WORLD How, then, can we explain the absence of humming birds from the English landscape and of titmice from Panama, and the pres ence of both in New England? Why are blackbirds and orioles, vireos and phaino peplas, confined to the New World, while waxwings and shrikes are found on both sides of the Atlantic and Pacific Oceans?t Evolution has taught us that all species of birds and animals were not created at the same time, and that there has been a gradual extension of range as well as an evolution of structure. It is thus not diffi cult to conceive that each group of birds originated in some one part of the globe in distant past ages, and in succeeding ages endeavored to populate the world. That some should have been much more successful than others is understandable, because we know that to-day some birds are much more prolific, more aggressive, and more adaptable than others. Compare the starling and the skylark, * This is the eighth article, illustrated by paint ings by Major Allan Brooks, in the important GEOGRAPHIC series describing the bird families of the United States and Canada. The ninth article, "Wild Ducks and Geese of North America," with 16 pages of paintings in color by Major Brooks, will appear in an early number. t The bird called "blackbird" in Britain is really a thrush, closely related to our robin.