Quantitative Analysis of Prairie Grouse Vocalizations

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Abstract
The structure of homologous vocalizations of greater prairie-chickens (Tympanuchus cupido) and sharp-tailed grouse (T. [Pedioecetes] phasianellus) was studied during 4 mating seasons in northwestern Minnesota [USA]. In this region males of the 2 spp. form display grounds in similar areas and occasionally occur together in mixed grounds where they hold mutually exclusive territories. Hybrids constitute approximately 3% of the combined populations. This study tested the hypothesis that the structures of homologous vocalizations varied predictably with function to assist in reproductive isolation. Aggressive calls were more similar between the species than courtship calls. The dichotomous nature of the birds'' vocal systems could promote heterospecific spacing and inhibit mating. The calls of 2 hybrid males varied in complex ways from those of either parental species. Although prairies are poor environments for transmission of acoustical signals, both species of grouse depend heavily on vocalizations in their communication. Sound transmission is enhanced in these species by low frequencies, use of sound windows, and crepuscular displaying.