Many frogs form large choruses during their mating season in which males produce loud advertisement calls to attract females and repel rival males. High background noise levels in these social aggregations can impair vocal perception. In humans, spatial release from masking contributes to our ability to understand speech in noisy social groups. Here, we tested the hypothesis that spatial separation between target signals and 'chorus-shaped noise' improves the ability of female gray treefrogs (Hyla chrysoscelis) to perform a behavioral discrimination task based on perceiving differences in the pulsatile structure of advertisement calls. We used two-stimulus choice tests to measure phonotaxis (approach toward sound) in response to calls differing in pulse rate along a biologically relevant continuum between conspecific (50pulsess-1) and heterospecific (20pulsess-1) calls. Signals were presented in quiet, in colocated noise, and in spatially separated noise. In quiet conditions, females exhibited robust preferences for calls with relatively faster pulse rates more typical of conspecific calls. Behavioral discrimination between calls differing in pulse rate was impaired in the presence of colocated noise but similar between quiet and spatially separated noise conditions. Our results indicate that spatial release from energetic masking facilitates a biologically important temporal discrimination task in frogs. We discuss these results in light of previous work on spatial release from masking in frogs and other animals.
Bibliographical noteFunding Information:
This work was supported by NIDCD R01 DC009582 . We thank, Alejandro Vélez for recordings of natural choruses and help generating chorus-shaped noise maskers, Mark Crawford, Madeleine Linck, John Moriarty, Ed Quinn, and Don Pereira for access to frog breeding sites, Sandra Tekmen for organizing collecting crews, and numerous undergraduate research assistants for help collecting and testing frogs.
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