FRIENDS OF EDGEWOOD NATURAL PRESERVE
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FRIENDS OF EDGEWOOD NATURAL PRESERVE
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BIRD SONG (PART 1) By Lee Franks The advent of the breeding season each spring is announced at dawn by a chorus of bird song that continues intermittently throughout the day. With practice, birders can identify a species by its songs and calls even without seeing the vocalizer, and we infer that birds can similarly distinguish between members of their own and other species by voice alone. But “when” and “how” is song learned? How does each species “know” which sounds are appropriate and should be learned. The answers to these and other related questions have long served as a focus of research by ornithologists. Learning songs and singing them is not easy for birds. The feats they accomplish for their small size are quite incredible. Learning is a gradual process that takes place over a period of weeks or months, and is often restricted to an early age. Typically, a vague, jumbled “subsong” appears first. Within a month or so, a subsong develops into the first attempts at producing mature but unstructured repertoires. Much more material may be developed than is actually needed for the eventual repertoire, but eventually the young bird selects a few syllables, perfects them, and organizes them into a correct pattern. Some young sparrows use only 1/4 of the syllables they learned and practiced in early phases of song development. Where do birds get their songs from? Studies of song learning have led to the “auditory template hypothesis”—the idea that each species is born with a neurological model of what its song should sound like, and it develops that song by matching sounds that it hears from older singing birds with the template in its brain. This process enables a young bird to filter out inappropriate sounds and to produce sounds matching the template. Song learning is selective, so that if offered a choice, birds will learn their own species’ song. If offered only songs of other species or if reared in isolation, learning does not occur and only a simplified approximation to the normal song develops. The vocal virtuosity of birds stems from the structure of their unusual and powerful vocal apparatus. Birds do not have a larynx like we do. Instead they have a syrinx, a unique organ located in the body cavity at the junction of the trachae and the primary bronchi. The syrinx is the equivalent of the human sound box. It contains membranes which vibrate and generate sound waves when air from the lungs is passed over them. The muscles of the syrinx control the details of sound production; birds with more elaborate vocal muscles produce more complex songs. But unlike our sound box, which is situated at the top of the trachea, the birds’ syrinx is set much lower down, at the junction of the two bronchi (air tubes) leading to the lungs. This means that the syrinx has two potential sound sources, one in each bronchus. The separate membranes on each bronchus produce separate sounds, which are then mixed when fed into the higher vocal tract. This complex design means that the bird can sing two different notes at the same time or even sing a duet with itself. The loud, complex territorial songs of birds are among their most conspicuous and familiar vocal displays. Usually these are long-distance communications (carrying 50 to 200 meters or more) and convey information about the identity, location, and motivation of the singer. Territorial songs serve as signals to potential rivals that the territory is occupied by a resident male prepared to protect his exclusive use of that space and any associated females. Inseparably coupled to the warning message is advertisement to unmated females. Female attraction to territorial male song is the first step toward courtship and pair formation. Included in the acoustical structure of songs are features that birds use for both species and individual recognition. Birds sing songs as well as give calls. Songs are constructed differently and serve a different purpose. It is bird song which has captured our hearts; however, bird song and singing is limited to only one order of birds, out of 30 that exist, namely Passeriformes (5712 species worldwide). Even then not all passerines (the name given to species within the order) sing songs and less than half the birds in Edgewood Park are genuine songsters. In Part 2 I'll discuss Song Dialects, Bird Calls, and Mimicry. 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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