Many temperate zone breeding birds spend their non-breeding period in the tropics where they defend individual territories. Unlike tropical birds that use song for breeding and non-breeding territorial defense, vocal defense differs strikingly between breeding and non-breeding territories in migrants. Song, restricted to males, is used during defense of breeding territories but callnotes are used to defend non-breeding territories. To explain why callnotes and not songs predominate in the non-breeding context, we present an empirical model based upon predictions from motivational/structural rules, ranging theory and latitudinal differences in extra-pair mating systems. Due to sex role divergence during breeding that favors singing in males, but not females, females may be unable to range male song. Ranging requires a signal to be in both the sender and receiver’s repertoire to allow the distance between them to be assessed (ranged). Non-breeding territories of migrants are defended by both males and females as exclusive individual (androgynous) territories. Ranging Theory predicts callnotes, being shared by both males and females can, in turn, be ranged by both so are effective in androgynous territoriality. Where songs are used for non-breeding territorial defense both sexes sing, supporting the evolutionary significance of shared vocalizations in androgynous territorial defense. 1. Introduction A continuing challenge in evolution is to identify the sources of selection acting on signal structure in vocal communication. Research has recently shifted from an emphasis on information transfer, wherein the sender’s goals determine signal structure, to the receiver’s goals (e.g., [1]). Under the receiver control model, receiver assessment of signals feeds back to the sender by influencing what the sender’s signals have accomplished [2–4]. Assessment insures that signals are honest and allows us to identify results of sexual conflict (Sensu [5]). Here, we provide an example of how signal assessment can produce seasonal signal structure changes in the same individuals in the context of territorial defense. Many migrant birds are territorial in temperate-zone-breeding areas and resume territorial behavior when they reach nonbreeding areas. They are, in essence, territorial throughout the year but breeding and nonbreeding territories are widely separated, often thousands of kilometers apart, in space as well as in time [6]. There are major changes in territorial behavior between breeding and nonbreeding periods that affect the context of communication. While
References
[1]
E. Font and P. Carazo, “Animals in translation: why there is meaning (but probably no message) in animal communication,” Animal Behaviour, vol. 80, no. 2, pp. e1–e6, 2010.
[2]
T. Guilford and M. S. Dawkins, “Receiver psychology and the evolution of animal signals,” Animal Behaviour, vol. 42, no. 1, pp. 1–14, 1991.
[3]
D. H. Owings and E. S. Morton, Animal Vocal Communication: A New Approach, Cambridge University Press, Cambridge, UK, 1998.
[4]
E. S. Morton, R. G. Coss, and D. H. Owings, “Mitogenetic rays and the information metaphor,” in Animal Communication Theory: Information and Influence, U. E. Stegmann, Ed., Cambridge University Press, Cambridge, UK, In press.
[5]
G. Arnqvist and L. Rowe, Sexual Conflict, Princeton University Press, Princeton, NJ, USA, 2005.
[6]
J. H. Rappole, The Ecology of Migrant Birds, Washington, DC, USA, 1995.
[7]
E. S. Morton, “Adaptations to seasonal changes by migrant land birds in the Panama Canal Zone,” in Migrant Birds in the Neotropics: Ecology, Behavior, Distribution, and Conservation, A. Keast and E. S. Morton, Eds., pp. 437–453, Smithsonian Institution Press, Washington, DC, USA, 1980.
[8]
P. P. Marra and R. T. Holmes, “Consequences of dominance-mediated habitat segregation in American Redstarts during the nonbreeding season,” Auk, vol. 118, no. 1, pp. 92–104, 2001.
[9]
B. J. M. Stutchbury, E. S. Morton, and T. E. Pitcher, “Sex roles in migrants: extra-pair mating systems and winter social systems,” in Birds of Two Worlds: The Ecology and Evolution of Migratory Birds, R. Greenberg and P. Marra, Eds., pp. 307–320, Johns Hopkins University Press, Baltimore, Md, 2005.
[10]
E. S. Morton, “Habitat segregation by sex in the hooded warbler: experiments on proximate causation and discussion of its evolution,” American Naturalist, vol. 135, no. 3, pp. 319–333, 1990.
[11]
D. R. Norris, P. P. Marra, T. K. Kyser, T. W. Sherry, and L. M. Ratcliffe, “Tropical winter habitat limits reproductive success on the temperate breeding grounds in a migratory bird,” Proceedings of the Royal Society B: Biological Sciences, vol. 271, no. 1534, pp. 59–64, 2004.
[12]
D. R. Norris, “Carry-over effects and habitat quality in migratory populations,” Oikos, vol. 109, no. 1, pp. 178–186, 2005.
[13]
E. S. Morton, “Predictions from the ranging hypothesis for the evolution of long distance signals in birds,” Behavior, vol. 99, no. 1-2, pp. 65–86, 1986.
[14]
E. S. Morton, “On the occurrence and significance of motivation-structural rules in some bird and mammal sounds,” American Naturalist, vol. 3, pp. 855–869, 1977.
[15]
D. G. Richards, “Estimation of distance of singing conspecifics by the Carolina wren,” Auk, vol. 98, pp. 127–133, 1981.
[16]
P. K. McGregor, “Sound cues to distance: the perception of range,” in Perception and Motor Control in Birds, M. N. O. Davies and P. R. Green, Eds., pp. 74–94, Springer, Berlin, Germany, 1994.
[17]
E. S. Morton, “Why songbirds learn songs: an arms race over ranging?” Poultry and Avian Biology Reviews, vol. 7, no. 1, pp. 65–71, 1996.
[18]
E. S. Morton, B. J. M. Stutchbury, J. S. Howlett, and W. H. Piper, “Genetic monogamy in blue-headed vireos and a comparison with a sympatric vireo with extrapair paternity,” Behavioral Ecology, vol. 9, no. 5, pp. 515–524, 1998.
[19]
E. S. Morton, J. Howlett, N. C. Kopysh, and I. Chiver, “Song ranging by incubating male Blue-headed Vireos: the importance of song representation in repertoires and implications for song delivery patterns and local/foreign dialect discrimination,” Journal of Field Ornithology, vol. 77, no. 3, pp. 291–301, 2006.
[20]
J. F. Prather, S. Peters, S. Nowicki, and R. Mooney, “Precise auditory-vocal mirroring in neurons for learned vocal communication,” Nature, vol. 451, no. 7176, pp. 305–310, 2008.
[21]
J. R. Krebs, R. Ashcroft, and K. V. Orsdol, “Song matching in the great tit Parus major L,” Animal Behaviour, vol. 29, no. 3, pp. 918–923, 1981.
[22]
E. S. Morton, “A comparison of vocal behavior among tropical and temperate passerine birds,” in Ecology and Evolution of Acoustic Communication in Birds, D. E. Kroodsma and T. E. Miller, Eds., pp. 258–268, Cornell University Press, Ithaca, NY, USA, 1996.
[23]
B. J. M. Stutchbury and E. S. Morton, Behavioral Ecology of Tropical Birds, Academic Press, London, UK, 2001.
[24]
J. F. Prather, S. Nowicki, R. C. Anderson, S. Peters, and R. Mooney, “Neural correlates of categorical perception in learned vocal communication,” Nature Neuroscience, vol. 12, no. 2, pp. 221–228, 2009.
[25]
E. S. Morton, “An evolutionary view of the origins and functions of avian vocal communication,” Japanese Journal of Ornithology, vol. 49, pp. 69–78, 2000.
[26]
W. M. Schleidt, “Tonic communication: continual effects of discrete signs in animal communication systems,” Journal of Theoretical Biology, vol. 42, no. 2, pp. 359–386, 1973.
[27]
J. R. Krebs, “Song and territory in the great tit Parus major,” in Evolutionary Ecology, B. Stonehouse and C. Perrins, Eds., pp. 47–62, MacMillon, London, UK, 1977.
[28]
D. G. Richards and R. H. Wiley, “Reverberations and amplitude fluctuations in the propagation of sound in a forest: implications for animal communication,” American Society of Naturalists, vol. 115, pp. 381–399, 1980.
[29]
B. S. Nelson, “Avian dependence on sound pressure level as an auditory distance cue,” Animal Behaviour, vol. 59, no. 1, pp. 57–67, 2000.
[30]
D. A. Spector, “Definition in biology: The case of 'bird song',” Journal of Theoretical Biology, vol. 168, no. 4, pp. 373–381, 1994.
[31]
J. Klicka, K. Burns, and G. M. Spellman, “Defining a monophyletic Cardinalini: a molecular perspective,” Molecular Phylogenetics and Evolution, vol. 45, no. 3, pp. 1014–1032, 2007.
[32]
R. Howard and A. Moore, The Howard and Moore Complete Checklist of the Birds of the World, Princeton University Press, Princeton, NJ, USA, 2003.
[33]
I. J. Lovette, J. L. Pérez-Emán, J. P. Sullivan et al., “A comprehensive multilocus phylogeny for the wood-warblers and a revised classification of the Parulidae (Aves),” Molecular Phylogenetics and Evolution, vol. 57, no. 2, pp. 753–770, 2010.
[34]
S. Mabey, Demography and territorial behavior of wintering Kentucky Warblers in Panama, M.S. thesis, University of Maryland, College Park, Md, USA, 1992.
[35]
E. S. Morton, J. F. Lynch, K. Young, and P. Mehlhop, “Do male Hooded Warblers exclude females from nonbreeding territories in tropical forests?” Auk, vol. 104, pp. 133–135, 1987.
[36]
P. Marler, “Characteristics of some animal calls,” Nature, vol. 176, no. 4470, pp. 6–8, 1955.
[37]
J. H. Rappole and D. W. Warner, “Ecological aspects of migrant bird behavior in Veracruz, Mexico,” in Migrant Birds in the Neotropics: Ecology, Behavior, Distribution, and Conservation, A. Keast and E. S. Morton, Eds., pp. 353–393, Smithsonian Institution Press, Washington, DC, USA, 1980.
[38]
R. Greenberg, D. K. Niven, S. Hopp, and C. Boone, “Frugivory and coexistence in a resident and a migratory vireo on the Yucatan Peninsula,” Condor, vol. 95, no. 4, pp. 990–999, 1993.
[39]
T. H. Hamilton, “Adaptive variation in the genus Vireo,” Wilson Bulletin, vol. 70, pp. 306–345, 1958.
[40]
B. L. Van Roo, E. D. Ketterson, and P. J. Sharp, “Testosterone and prolactin in two songbirds that differ in paternal care: the blue-headed vireo and the red-eyed vireo,” Hormones and Behavior, vol. 44, no. 5, pp. 435–441, 2003.
[41]
E. S. Morton, B. M. J. Stutchbury, and I. Chiver, “Parental conflict and brood desertion by females in blue-headed vireos,” Behavioral Ecology and Sociobiology, vol. 64, pp. 947–954, 2010.
[42]
R. Greenberg and J. S. Ortiz, “Interspecific defense of pasture trees by wintering yellow warblers,” Auk, vol. 111, no. 3, pp. 672–682, 1994.
[43]
D. L. Neudorf and S. A. Tarof, “The role of chip calls in winter territoriality of yellow warblers,” Journal of Field Ornithology, vol. 69, no. 1, pp. 30–36, 1998.
