Function, perception and evolution of complex bird songs: Like many species of birds, individual song sparrow males each sing a repertoire of different song types. Song sparrow repertoires are particularly complex because song types themselves may vary considerably among successive renditions by the same bird. In several ongoing studies, we are investigating the function of different levels of variation in song sparrow song. These studies include field playback experiments to determine how birds themselves perceptually classify songs, field experiments (e.g., male removal/speaker replacement tests) and laboratory experiments (e.g., female copulation solicitation assays) that ask how patterns of variation influence receivers' responses to song, and song learning experiments that examine how experience influences the expression of variation.

Recent publications:
Nowicki, S, W. A. Searcy, T. Krueger & M. Hughes. Individual variation in response to simulated territorial challenge among territory-holding song sparrows. Journal of Avian Biology, in press.
Peters, S., W. A. Searcy, M. D. Beecher & S. Nowicki. 2000. Geographic variation in the organization of song sparrow repertoires. Auk 117: 936-942.
Searcy, W. A., S. Nowicki & C. Logan. 2000. Song type variants and aggressive signaling. Behavioral Ecology and Sociobiology 48: 358-363.
Nowicki, S., S. Peters, W. A. Searcy, & C. Clayton. 1999. The development of within-song type variation in song sparrows. Animal Behaviour 57: 1257-1264.

Song as an indicator mechanism: testing the "nutritional stress hypothesis:" Many studies have shown that female birds mate preferentially with males having larger song repertoires. What remains unclear is why larger repertoires function better as signals for mate attraction. Presumably, females benefit by mating with males having particular songs characteristics, but what is the mechanism by which they benefit? We are currently developing and testing a new hypothesis - the "nutritional stress hypothesis" - which proposes that aspects of singing behavior such as repertoire complexity provide females with a reliable indicator of male quality, based on the relationship between early nutritional stress, brain development, and song learning. In the laboratory, we are comparing song learning in swamp sparrows and song sparrows raised under different nutritional conditions, to determine if features of song known to influence female choice reflect early stress. In collaboration with Dennis Hasselquist and Staffan Bensch at Lund University, Sweden, we have used data from a field population of great reed warblers to test the prediction that nestling condition correlates with subsequent song production by adults.

Recent publications:
Nowicki, S., D. Hasselquist, S. Bensch & S. Peters. 2000. Nestling growth and song repertoire size in great reed warblers: evidence for song learning as an indicator mechanism in mate choice. Proceedings of the Royal Society of London B 267: 2419-2424.
Nowicki, S., S. Peters & J. Podos. 1998. Song learning, early nutrition and sexual selection in songbirds. American Zoologist 38: 179-190.

Song production mechanisms and motor constraints on song evolution: Earlier work in the Nowicki lab demonstrated the importance of the avian vocal tract - especially beak movements and their influence on vocal tract acoustics - for the production of birdsong. In addition to extending this work, we are now also exploring how performance limitations imposed by production mechanisms may influence song development and evolution. One focus of this work builds on the finding by Jeff Podos that young swamp sparrows attempting to learn songs having faster-than-normal trill rates produce a novel "broken syntax" not normally observed in this species. In ongoing studies, we are exploring how this novel syntax affects the responses of both males and females in functional contexts, as well as whether this novel song feature can be transmitted culturally through song learning, both with an eye to asking how motor constraints might lead to large-scale reorganization of song structure during song evolution.

Recent publications:
Nowicki, S., W. A. Searcy, M. Hughes & J. Podos. 2001. The evolution of bird song: male and female response to song innovation in swamp sparrows. Animal Behaviour, in press.
Hoese, W. J., J. Podos, N. C. Boetticher & S. Nowicki. 2000. Vocal tract function in birdsong production: experimental manipulation of beak movements. Journal of Experimental Biology 203: 1845-1855.
Podos, J., S. Nowicki & S. Peters. 1999. Permissiveness in the learning and development of song syntax in swamp sparrows. Animal Behavior 58: 93-103.

Auditory encoding of multiple song types by song system neurons: The telencephalic nucleus HVc in the songbird brain is essential for the production and perception of song, and many HVc neurons display highly selective auditory responses, generating more action potentials in response to playback of the bird's own song (BOS) than to reverse BOS or other conspecific songs. To date, such song-selective neurons have been studied exclusively in species that produce only a single song type. In the case of birds singing multiple song types, however, vocal development and song perception additionally require neuronal mechanisms capable of discriminating among different songs in an individual's repertoire, rather than simply discriminating a single BOS from all other songs. In collaboration with Rich Mooney in the Department of Neurobiology, we have begun to characterize response properties of HVc neurons in the swamp sparrow, a multiple song type species. Understanding these response properties will help uncover general mechanisms by which song-specificity is generated in the bird's brain. Further, this work will explore whether the HVc response properties we observe provide a basis for categorical perception, in which continuously varying stimuli are partitioned into discrete perceptual categories, such as has been shown to occur in song perception by swamp sparrows using behavioral methods.

Website last modified August 2001