Effects of species, sex and season on auditory processing in songbirds

Megan Drewe Gall, Purdue University

Abstract

Auditory receptive space is thought to be shaped by selective pressure to detect vocalizations. For many songbirds, this results in a close match between vocal production and auditory receptive space because song plays a key role in both territorial defense and mating success. Vocal production is species, sex, and season specific in most songbirds. Concomitantly, the selective pressure to detect vocalizations may vary with species, sex or season and may result in auditory processing plasticity. I investigated the auditory processing of seven species of songbirds (American tree sparrow, brown-headed cowbird, dark-eyed junco, house finch, house sparrow, red-winged blackbird and white-crowned sparrow) using auditory evoked potentials. In these species I assessed: (1) coding of structural features (2) temporal resolution (3) frequency selectivity and (4) frequency sensitivity. I found that in most species there is a close correlation between vocal signals and the coding of structural features such as signal onset and frequency range. However, in the brown-headed cowbird, an obligate brood parasite, there was a mismatch between the high frequency vocalizations and the range of frequency sensitivity, and between vocal onset patterns and onset coding. The mismatch between auditory processing and vocalizations may be due to selection acting on the auditory system that facilitates host localization through host song. Interestingly, during the breeding season brown-headed cowbird females had greater frequency sensitivity and greater frequency selectivity than males. This could enhance host detection or mate selection in females. Finally, in the house sparrow, I found that during the non-breeding season there are no differences between males and females in frequency selectivity or temporal resolution. However, during the breeding season females have enhanced frequency selectivity, which comes at the expense of temporal resolution, while males exhibit no change. Enhanced frequency selectivity in females should improve the coding of temporal fine structure and the ability to discriminate among potential mates. Taken together, these results suggest that selective pressure to detect ecologically relevant acoustic stimuli is a primary factor in shaping auditory processing abilities in songbirds. For the brown-headed cowbirds ecologically relevant stimuli include not only conspecific vocalizations, but also the vocalizations of heterospecific hosts.

Degree

Ph.D.

Advisors

Lucas, Purdue University.

Subject Area

Neurosciences|Ecology|Physiology

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