Younger years old in 1930 yet the painting shows a

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Unformatted text preview: inly in territorial behavior. In the second, several song types in bouts before switching to another, the female choice and intersexual selection produce longer, warbler continuously composes much longer and more more complicated songs used mainly in mate attraction; variable songs without repetition. For the first time, like such visual ornamentation as the peacock's tail, researchers found a significant correlation between elaborate vocal characteristics increase the male's chances repertoire size and early mating, and they discovered of being chosen as a mate, and he thus enjoys more further that repertoire size had a more significant effect reproductive success than his less ostentatious rivals. The than any other measure of male quality on the number of two pathways are not mutually exclusive, and we can young produced. The evidence suggests that warblers use expect to find examples that reflect their interaction. their extremely elaborate songs primarily to attract females, Teasing them apart has been an important challenge to clearly confirming the effect of intersexual selection on the evolutionary biologists. evolution of birdsong. Early research confirmed the role of intrasexual (462 words) selection. In a variety of experiments in the field, males responded aggressively to recorded songs by exhibiting territorial behavior near the speakers. The breakthrough for research into intersexual selection came in the development of a new technique for investigating female response in the laboratory. When female cowbirds raised in isolation in soundproof chambers were exposed to recordings of male song, they responded by exhibiting mating behavior. By quantifying the responses, researchers were able to determine what particular features of the song were most important. In further experiments on song sparrows, researchers found that when exposed to a single song type repeated several times or to a repertoire of different song types, females responded more to the latter. The beauty of the experimental design is that it effectively rules out confounding variables; acoustic isolation assures that the female can respond only to the song structure itself. If intersexual selection operates as theorized, males with more complicated songs should not only attract females more readily but should also enjoy greater reproductive success. At first, however, researchers doing fieldwork with song sparrows found no correlation between larger repertoires and early mating, which has been shown to be one indicator of reproductive success; further, common measures of male quality used to predict reproductive success, such as weight, size, age, and 188 3. The passage is primarily concerned with 5. The passage indicates that researchers raised female (A) showing that intrasexual selection has a greater cowbirds in acoustic isolation in order to effect on birdsong than does intersexual selection (A) eliminate confounding variables (B) contrasting the role of song complexity i...
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