Discrimination of natural contact calls by two strains of canary and the budgerigar

Abstract

Animals and their communication signals make up a unique environmental world. The sender of the signal, the signal itself, and the receiver interact to produce a complex communication system. Evidence is accumulating that many species of animal are especially adapted not only for producing species-specific communication signals, but also for perceiving such signals (Marler 1984; Dooling & Hulse 1989). We recently reported an experiment in which budgerigars and Belgian Waterslager canaries were trained to discriminate both budgerigar and canary calls in an operant procedure (Park, Okanoya & Dooling 1985). Budgerigars were equally adept at learning to discriminate among canary calls as well as budgerigar calls. The canaries were more adept at discriminating among canary calls than budgerigar calls, but the canaries' overall discrimination rate was much lower than the budgerigars'. Furthermore, the 2 species were equally adept at learning to discriminate among pure tones biologically irrelevant acoustic stimuli for both species. While these results could be used to support the notion of species-specific perceptual adaptation in canaries, they also reveal that canaries may be far less adept at learning to discriminate among complex calls than budgerigars. One possible explanation might be that the auditory sensitivity of canaries is not as good as that of budgerigars. Okanoya & Dooling (1985, 1987) found that a population from the Waterslager strain of canary expressed an elevation in auditory sensitivity. Waterslagers have auditory thresholds 30 to 40 dB higher in the middle to high frequency region of the audiogram compared to other strains of canaries, including German Rollers and American Singers tested with the same procedures. Though Belgian Waterslager canaries have poor high frequency sensitivity, birds from our colony and colonies in other laboratories have no difficulty in breeding. This means that males of the strain are apparently able to use auditory information to learn and successfully use song to elicit reproductive behaviors from females. Still, because a great deal of information on neurophysiological correlates to song development has come from Waterslager canaries (Nottebohm 1984), the recent finding 'of abnormal hearing in the strain raises important questions. For instance, do the elevated thresholds affect reproductive success by hindering or even facilitating learning and reproductive behaviors? The present experiments were designed to further explore the effects of poor high-frequency hearing on perceptual learning of biologically relevant stimuli in an experimental situation. We wanted to know if the species differences we originally reported were due to differences in learning ability or due to species differences in high-frequency auditory sensitivity. To this end, we tested canaries from a strain with normal hearing and compared the results to the same budgerigars and Waterslager canaries used in the previous study. Method Subjects