676 Animal Behaviour, 33, 2 per individual (Kroodsma 1974). The wrentit has a relatively simple song, which shows little within- individual variability (Boarman 1985). The energy spectra of the two species' songs do partially overlap, however; the modal frequency of the wrentit's is considerably lower than that of the Bewick's wren (Boatman 1985). Hence, some acoustical interference may occur when the two songs overlap, but the extent of this is limited (but see Bremond 1977). The wrentit, having a single stereotyped song, may be affected more by this interference. The Bewick's wren may avoid inter- ference with greater variability in its song; fewer portions of its song overlap spectrally with the wrentit's song than vice versa. Results from further analyses of an experimental nature would be desirable (i.e. playbacks, removals, etc.). We thank S. I. Rothstein for permission to use Hughell's data and J. P. Myers for suggesting cross-correlation. S. I. Rothstein, R. Payne, L. Baptista, E. Morton and an anonymous referee commented on previous drafts. ROBERT C. FLEISCHER* WILLIAMI. BOARMAN~'w MARTIN L. CODY~ *Department of Biological Sciences, University of California, Santa Barbara, CA 93106, U.S.A. t Department of Biological Sciences, San Francisco State University, San Francisco, CA 94132, U.S.A. ~Department of Biology, University of California, Los Angeles, CA 90024, U.S.A. w address: Department of Biological Sciences, Rutgers University, Piscataway, NJ 08854, U.S.A. References Boarman, W. I. 1985. Habitat acoustics and the vocal structure of a Califorinia songbird community. M.A. thesis, San Francisco State University. Bremond, J. C. 1977. Acoustic competition between the song of the wren (Troglodytes troglodytes) and the songs of other species. Behaviour, 65, 89-98. Cody, M. L. & Brown, J. H. 1969. Song asynchrony in neighbouring bird species. Nature, Lond., 222, 778-780. Ficken, R. W., Ficken, M. S. & Hailman, J. P. 1974. Temporal pattern shifts to avoid acoustic interference in singingbirds. Science, N.Y., 183, 76~763. Gochfeld, M. 1978. Intraspecific social stimulation and temporal displacement of songs of the lesser skylark, Alauda gulgula. Z. Tierpsyehol., 48, 337-344. Kroodsma, D. E. 1974. Song learning, dialects and dispersal in the Bewick's wren. Z. Tierpsychol., 35, 352-380. Marler, P. 1960. Bird songs and mate selection. In: Animal Sounds and Communication (Ed. by W. E. Lanyon & W. N. Tavolga), pp. 348-367. Washington, D.C.: American Institute of BiologicalScience. Miller, E. H. 1982. Character and variance shift in acousticsignalsof birds. In: Acoustic"Communication in Birds (Ed. by D. E. Kroodsma & E. H. Miller), pp. 253 295. New York: Academic Press. Wiley, R. H. & Richards, D. G. 1982. Adaptations for acoustic communication in birds: sound transmission and signal detection. In: Acoustic Communication in Birds (Ed. by D. E. Kroodsma & E. H. Miller), pp. 131-181. New York: Academic Press. (Received 29 March 1984; revised 12 October 1984; MS. number As-278) Dispersal and Inbreeding Avoidance In a recent highly selective review, Moore & Ali (1984) argue that dispersal patterns in vertebrates have evolved independently of the consequences of inbreeding avoidance, but they virtually ignore a considerable body of evidence to the contrary. They selectively cite my paper on olive baboons (Papio anubis) to give the impression that I consi- dered inbreeding avoidance to be the only cause of dispersal, when in fact I made detailed comparisons of natal dispersal and breeding dispersal by males, and I emphasized that considerable dispersal occurred that could not have been the result of inbreeding avoidance (Packer 1979, pages 10-13). For example, a large proportion of males transfer several times during their lives. Secondary move- ments by males do not coincide with their daughters reaching sexual maturity, but instead consist of migration into troops with greater numbers of oestrous females. However, I specifically tested the possibility that male natal dispersal was a mechanism for avoiding close inbreeding, and my results consistently sup- ported that hypothesis. Moore & Ali seriously misrepresent my work and cursorily dismiss the work of others who have made similar findings. Since space does not allow a comprehensive reply (instead, see Pusey & Packer, in press), I will only address the following six points concerning nay own work. First, the only quantitative data presented in their paper concern the infant mortality in A troop prior to the migration of a male to a branch of his natal troop (see Packer 1979 for details). They suggest that infant mortality in that troop was already high prior to the male's achieving high mating success, and thus that the mortality that I had attributed to inbreeding depression may have