In several ways bird song provides a unique model system for studying not only function, evolution, and ontogeny but also the neural control of behavior patterns. First, the behaviors can be tape-recorded and analyzed quantitatively. Second, a rich comparative potential exists because all songbirds differ from each other in either subtle or dramatic ways; careful selection of subjects allows a dissection of the selective forces that have produced such a diversity of behaviors among birds with different ecologies or mating systems. Third, the development of these behavioral patterns can readily be studied by hand-rearing birds and manipulating their environment in the laboratory. And, fourth, these behaviors are controlled by a discrete neural circuitry, study of which has yielded exciting glimpses of the neural substrates of vocal learning.
One of our goals has been to understand the diversity of singing behaviors found among Cistothorus wrens. Males of western populations of marsh wrens (C. palustris), for example, have larger song repertoires (as many as 200 songs), more rapid and versatile singing behaviors, and larger neural control centers than do their eastern counterparts. Studies of marsh wren populations throughout the United States and Canada, and especially in an overlap zone in Saskatchewan, will help us understand the evolution of large song repertoires, their neural control, and the relationship between biological and cultural evolution.
Donald E. Kroodsma
Acoustic Communication
in Birds
in Birds
A related effort is our current survey of other Cistothorus species throughout North and South America, in which we hope to understand the evolution of song ontogeny and function by studying the ecological context in which they occur. Our second focus is again comparative, but this time at the species level and in a different songbird family. Although many species, such as the marsh wren, have repertoires of general-purpose songs that are all used interchangeably in both territorial advertisement and mate attraction or stimulation, many New World warblers (Parulinae) sing two different songs or groups of songs in different contexts. One behavior seems directed at males, the other perhaps at females. In our studies of these warblers we hope to understand not only how the birds use these behaviors in nature, but also the exact function of the different song forms or behaviors; when, if, and from whom they learn these behaviors; and exactly how they know when to use the appropriate behaviors.
Our third, also comparative, focus is at the suborder level. The songbirds, to which the wrens and warblers belong, and the "suboscines" are two suborders of the same avian order Passeriformes. Songbirds learn to sing, have local dialects, and have discrete song control centers in the forebrain. Songs of suboscines, such as flycatchers, are not learned from other individuals and do not show local dialects. Furthermore, no evidence of the songbird song control centers in the forebrain can be found. In our studies of flycatchers, we hope to understand the limits and functions of song variation among suboscines, the neural control of nonlearned songs, and perhaps the evolutionary substrate from which songbird song imitation was derived.
Our goals are, quite simply, to understand, through observations and experiments in both the laboratory and the field, the diversity and evolution of vocal behaviors among birds. The rich variety of subjects, both at our doorstep and beyond, such as in the tropics, provides a wealth of material for our curiosity.
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