FRIENDS OF EDGEWOOD NATURAL PRESERVE
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FRIENDS OF EDGEWOOD NATURAL PRESERVE
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BIRD SONG (PART 2) By Lee Franks This is the second of 2 installments by Lee on this subject. Part 1 appeared in the March 2006 newsletter and described how birds learn songs and the mechanics of producing such complex sounds. —ed. Nearly half of the birds in the world do not sing. They are not, however, silent. Far from it. All birds use sounds to communicate. Most use vocalizations that are short and unmusical and cannot be termed as song. These sounds have considerable functionality and are labeled call-notes or calls, to distinguish them from true song. Birds generally have 5 to 15 distinct calls with a variety of overlapping functions. These functions include proclamation of territorial ownership, warnings of potential dangers, and maintenance of social contact. Most have some calls that are used only for occasional special purposes. Contact or association calls, for instance, help birds keep track of one another while foraging or when in dense vegetation. Alarm calls signal danger and advise escape flight. Birds start using calls early in their lives, in some species even before they are hatched. Quail chicks are able to communicate with each other and their mother from inside their eggs. They are thus able to synchronize hatching so that they emerge from the eggs within the space of a couple of hours. Dialects Just as our speech patterns vary regionally, the songs of many birds also show geographic variation. Local variants are called dialects. They are commonly found in songbirds with populations restricted to particular habitats (coastal, for example), and separated from other populations by unsuitable terrain. The song of the Spotted Towhees, which are Edgewood residents, are composed of just a buzzy trill without any introduction. Vocal dialects appear to be learned. Young birds hear the songs sung around their natal territories by their fathers and neighboring males, and acquire the peculiarities of these renditions. Many ornithologists believe that dialects serve as indications of genetic adaptation to local conditions. The dialects thus enable females to choose males from their own birth area, who presumably carry genes closely adapted to the specific environment in which breeding occurs. Experimental work with several species has shown that females are more responsive to their own song dialects than to more distant song dialects. Mimicry When one species copies the vocalizations of another species, it is referred to as “vocal mimicry.” This vocal characteristic is well known in the Northern Mockingbird and the California Thrasher, both Edgewood residents, but little is known about its precise function, raising interesting questions. Do mockingbirds and thrashers communicate directly with the species they imitate? Do they use vocal mimicry to help exclude other species from breeding territories? Why are non-avian sounds such as the barking of dogs, screeching of machinery, human whistling, etc., sometimes incorporated into a bird’s repertoire? The answer to this last question may be simply that natural selection has favored a large and diverse repertoire in some species like the mockingbird and thrasher, and that one way of increasing repertoire size and diversity is to incorporate sounds from the surrounding acoustic environment. Some birds like Jays use vocal mimicry to attract help in mobbing of predators. Neighbors of the species being imitated then gather to scold and help discourage the predator. References Ornithology, Frank B. Gill ; W. H. Freeman and Company, New York Birder’s Handbook , A Field Guide To The Natural History Of North American Birds, Paul R. Ehrlich, David S. Dobkin, Darryl Wheye; Simon & Schuster Inc, New York |
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