Greene, Erick

English

University of Montana

University of Montana ScholarWorks at University of Montana Biological Sciences Faculty Publications Biological Sciences 4-1999 Toward an Evolutionary Understanding of Song Diversity in Oscines Erick Greene University of Montana - Missoula, erick.Greene@mso.umt.edu Follow this and additional works at: https://scholarworks.umt.edu/biosci_pubs  Part of the Biology Commons Let us know how access to this document benefits you. Recommended Citation Greene, Erick, "Toward an Evolutionary Understanding of Song Diversity in Oscines" (1999). Biological Sciences Faculty Publications. 296. https://scholarworks.umt.edu/biosci_pubs/296 This Editorial is brought to you for free and open access by the Biological Sciences at ScholarWorks at University of Montana. It has been accepted for inclusion in Biological Sciences Faculty Publications by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact scholarworks@mso.umt.edu. The Auk i A Quarterly Journal of Ornithology .2I7 Vol. 116 No. 2 April 1999 The Auk 116(2):299-301, 1999 OVERVIEWS TOWARD AN EVOLUTIONARY UNDERSTANDING OF SONG DIVERSITY IN OSCINES ERICK GREENE' Division of Biological Sciences, University of Montana, Missoula, Montana 59812, USA THE SONGS OF BIRDS are among the most com- plex and beautiful natural sounds, and they have captivated scientists, musicians, poets, and artists for thousands of years. Indeed, the vocal behavior of birds arguably has been stud- ied more intensively than any other aspect of avian biology. Oscine songbirds develop their songs through complex interactions between innate (i.e. genetic, or hard-wired) species-spe- cific developmental programs and social inter- actions (i.e. learning) during early life. The im- portance of learning in song development has long been recognized: teaching young birds to imitate melodies was a lucrative profession in Europe during the 17th and 18th centuries. Chicks were kept together in "classes" and ex- posed to tunes played on recorders. Once the young birds had copied these songs, they com- manded high prices at home and abroad. The "Bird Fancyer's Delight" (Anonymous 1717), most likely compiled by the British ornitholo- gist John Hamersley, contains many tunes "properly composed, within ye compass and faculty of each bird, for ye Wood-lark, Black- bird, Throustill, House-sparrow, Canary-bird, Black-thorn-Linnet, Garden-Bull-finch, and Starling." The interactions between learning and innate developmental events produce a bewildering diversity of vocal behavior among songbirds. Repertoire size (the number of songs sung by 1 E-mail: egreene@selway.umt.edu an individual male), for example, varies over three orders of magnitude. The number of song types an individual male sings varies from one (e.g. White-crowned Sparrows [Zonotrichia leu- cophrys]; Baptista 1975), to many (e.g. 10 to 60 in Sedge Warblers [Acrocephalus schoenobaenus]; Catchpole 1980), to hundreds (e.g. Common Nightingales [Luscinia megarhynchos]; Hultsch and Todt 1989), to even thousands (e.g. Brown Thrashers [Toxostoma rufum]; Boughey and Thompson 1981). At the population level, spe- cies differ in the similarity of songs of neigh- bors. At one extreme, individuals can share most or all of their song types with neighbors, resulting in considerable spatial structure and very sharp boundaries between different song dialects (i.e. miocrogeographic variation). At the other extreme, songs of neighbors can be dissimilar, with little geographic structure in the distribution of song types. Species also dif- fer in the degree to which they copy songs of other birds they hear during song develop- ment. Some species tend to faithfully imitate the songs they hear, whereas others tend to im- provise and develop individually distinct songs (Kroodsma 1996). Since the pioneering work of Thorpe (1958) on song learning in Chaffinches (Fringilla coe- lebs), many laboratory studies have been con- ducted on developmental aspects of song learn- ing. These important lab studies, by necessity, have focused on proximate "how" questions and have revealed much about the endocrine, 299 This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 19:00:24 PMAll use subject to JSTOR Terms and Conditions300 Overviews [Auk, Vol. 116 neurological, anatomical, and developmental mechanisms of song learning (see Nottebohm 1993, Marler 1984, Catchpole and Slater 1995, Beecher 1996, Hauser 1996). Lab studies, how- ever, cannot begin to replicate the complex eco- logical and social factors that undoubtedly play a crucial role in the evolution of vocal behavior of song birds. Kroodsma (1996:4) has framed this in saying: "Exactly what can laboratory studies ... tell us about how birds behave in nature? ... I am increasingly convinced that laboratory studies can at most show only what a bird is capable of doing in an environment never encountered before in the species' evo- lutionary history." How, for example, do migratory habits, dis- persal characteristics, intensity of sexual selec- tion, mating systems, habitat type, predation and parasitism, phylogeny, and other ecologi- cal and social variables influence the evolution of vocal behavior? Although many studies have investigated some of these factors (e.g. Morton 1975, Catchpole 1982, Searcy and Andersson 1986), many field studies are descriptive and remain unconnected to any larger set of hy- potheses. We currently lack a coherent concep- tual model that explains the diversity of sing- ing behavior and song learning programs in an evolutionary framework. A widespread need now exists for comparative studies, involving both laboratory analyses and fieldwork, that in- vestigate the ultimate mechanisms that influ- ence the evolution of vocal behavior (Catchpole and Slater 1995, Hauser 1996, Kroodsma 1996). In this issue of The Auk, Kroodsma et al. ex- amine differences in song development be- tween Marsh Wrens (Cistothorus palustris) and North American Sedge Wrens (Cistothorus pla- tensis). Their work is an exciting example of the type of comparative study that can shed new light on the evolution of vocal behavior and song learning styles. Don Kroodsma and his colleagues have combined lab and field studies of two Cistothorus wrens whose vocal behaviors appear to differ in fundamental ways. Males of both species have large repertoires, with indi- viduals singing 50 to 200 different song types. However, the species differ markedly in the de- gree of song sharing in local populations. Marsh Wrens tend to share many song types with neighbors, engage in bouts of matched countersinging during territorial interactions, and have song dialects that vary geographical- ly. In contrast, male Sedge Wrens share few song types with neighbors and show little geo- graphic variation in dialect structure. Earlier lab studies showed that young Marsh Wrens learn by imitation, faithfully copying tutor songs played to them on speakers (Kroodsma and Pickert 1984). Previous studies with Sedge Wrens suggested that young males improvise rather than imitate songs (Kroodsma and Ver- ner 1978). These studies were based on only three birds, however, and an alternative hy- pothesis remained that Sedge Wrens learn by imitation, but disperse long distances from where they were born, which would also result in no recognizable geographic song dialects. What ecological and social factors are re- sponsible for these differences in vocal behav- ior and possible differences in song learning programs (i.e. imitation vs. improvisation)? Both Marsh Wrens and Sedge Wrens breed in high densities and can have highly polygynous mating systems. However, differences in the stability of their breeding habitats may influ- ence other important characteristics of their life histories. Marsh Wrens breed in relatively sta- ble marshes, and they are either year-round residents, or if migratory, they show a high de- gree of site fidelity. Sedge Wrens breed in more ephemeral wet meadows, and it has been sug- gested that they are highly nomadic, opportu- nistic colonizers of these unpredictable habi- tats. Different song-learning programs may be favored in breeding habitats that differ in tem- poral stability. Highly philopatric Marsh Wrens that learn by imitation when they are young would thus develop a catalog of songs shared with neighbors. This imitative song- learning developmental program, coupled with relatively low dispersal, would reduce variation between individuals while maximiz- ing geographic differentiation. North Ameri- can Sedge Wrens may develop songs by impro- visation from a basic species-specific template. Such a song-learning program would maxi- mize individual variation while minimizing geographic differentiation. This improvisatory song-learning program would result in a wider signal audience, allowing a male to communi- cate with other Sedge Wrens no matter where it ended up. Although these general hypotheses had been formulated in the 1970s, the sample sizes of the preliminary work were small, and many of the This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 19:00:24 PMAll use subject to JSTOR Terms and ConditionsApril 1999] Overviews 301 underlying assumptions remained untested. Kroodsma and his co-workers (1999) have re- turned to this fascinating comparison. To un- ambiguously demonstrate that North Ameri- can Sedge Wrens do learn by improvisation, they captured nestlings from North Dakota and brought them into captivity. The young birds were exposed to a training tape for a year, and the young males could see and hear each other. Each male developed unique songs that were unlike those of the training tape or the other males (although they contained elements that were similar to the training tapes). Con- current field studies confirmed that North American Sedge Wrens are highly mobile and opportunistically disperse and settle in suit- able habitat when it becomes available between May and October. These lab and field studies confirm that song-learning programs of Marsh Wrens and Sedge Wrens are different. The re- sults are further bolstered with conspecific comparisons of more sedentary populations of South American Sedge Wrens. In Brazil, for ex- ample, Sedge Wrens breed in more stable hab- itats and are ecologically and socially more similar to North American Marsh Wrens than to North American Sedge Wrens; Brazilian males learn songs by imitation, and birds with- in the same marsh share many song types and engage in matched countersinging in a manner similar to that of North American Marsh Wrens. Kroodsma et al.'s study is an exciting exam- ple of how comparisons between judiciously chosen species can help frame hypotheses about the selective pressures that act on bird songs. With the example set by these research- ers, we can look forward to more studies that illuminate the how as well as the why of song learning and vocal behavior in oscines. LITERATURE CITED ANONYMOUS. 1717. The bird fancyer's delight. Rich- ard Mearnes, London. BAPTISTA, L. F. 1975. Song dialects and demes in sed- entary populations of the White-crowned Spar- row (Zonotrichia leucophrys nuttalli). University of California Publications in Zoology 105:1-52. BEECHER, M. D. 1996. Birdsong learning in the lab- oratory and field. Pages 61-78 in Ecology and evolution of acoustic communication in birds (D. E. Kroodsma and E. H. Miller, Eds.). Cornell University Press, Ithaca, New York. BOUGHEY, M. J., AND N. S. THOMPSON. 1981. Song va- riety in the Brown Thrasher (Toxostoma rufum). Zeitschrift fur Tierpsychologie 56:47-58. CATCHPOLE, C. K. 1980. Sexual selection and the evo- lution of complex songs among European war- blers of the genus Acrocephalus. Behaviour 74: 149-166. CATCHPOLE, C. K. 1982. The evolution of bird sounds in relation to mating and spacing behavior. Pag- es 297-319 in Acoustic communication in birds, vol. 1 (D. E. Kroodsma and E. H. Miller, Eds.). Academic Press, New York. CATCHPOLE, C. K., AND P. J. B. SLATER. 1995. Bird song: Biological themes and variations. Cam- bridge University Press, Cambridge, United Kingdom. HAUSER, M. D. 1996. The evolution of communica- tion. MIT Press, Cambridge, Massachusetts. HULTSCH, H., AND D. TODT. 1989. Song acquisition and acquisition constraints in the Nightingale, Luscinia megarhynchos. Naturwissenschaften 76: 83-85. KROODSMA, D. E. 1996. Ecology of passerine song de- velopment. Pages 3-19 in Ecology and evolution of acoustic communication in birds (D. E. Kroodsma and E. H. Miller, Eds.). Cornell Uni- versity Press, Ithaca, New York. KROODSMA, D. E., W.-C. Liu, E. GOODWIN, AND P. A. BEDELL. 1999. The ecology of song improvisation as illustrated by North American Sedge Wrens. Auk 116:373-386. KROODSMA, D. E., AND R. PICKERT. 1984. Sensitive phases for song learning: Effects of social inter- action and individual variation. Animal Behav- iour 32:389-394. KROODSMA, D. E., AND J. VERNER. 1978. Complex singing behaviors among Cistothorus wrens. Auk 95:703-716. MARLER, P. 1984. Song learning: Innate species dif- ferences in the learning process. Pages 289-309 in The biology of learning (P. Marler and H. S. Terrance, Eds.). Springer-Verlag, New York. MORTON, E. S. 1975. Ecological sources of selection on avian sounds. American Naturalist 109:17- 34. NOTTEBOHM, F. 1993. The search for neural mecha- nisms that define the sensitive period for song learning in birds. Netherlands Journal of Zool- ogy 43:193-234. SEARCY, W. A., AND M. ANDERSSON. 1986. Sexual se- lection and the evolution of song. Annual Re- view of Ecology and Systematics 17:507-533. THORPE, W. H. 1958. The learning of song patterns in birds, with especial reference to the song of the Chaffinch, Fringilla coelebs. Ibis 100:535-570. This content downloaded from 150.131.192.151 on Wed, 30 Oct 2013 19:00:24 PMAll use subject to JSTOR Terms and Conditions

Toward an Evolutionary Understanding of Song Diversity in Oscines

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Toward an Evolutionary Understanding of Song Diversity in Oscines

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