Figure 2.

Results of two-choice phonotaxis tests of level discrimination. (a) Depicted here are the proportions of females (N = 24 per test) choosing the un-attenuated alternative as a function of the level difference between the un-attenuated and attenuated alternatives. Error bars depict the 95% binomial confidence interval (one-tailed). Data are shown for tests conducted at nominal signal levels of 85 dB (circles) and 79 dB (triangles) in the presence (open symbols) and absence (filled symbols) of chorus-shaped noise. Asterisks indicate significance (P < 0.05) in one-tailed binomial tests of the hypothesis that proportions equaling 50% would choose both the attenuated and un-attenuated alternatives. (b) and (c) depict the probabilities of choosing the un-attenuated alternative for the 79 dB (b) and 85 dB (c) nominal signal levels as functions of level difference. Circles depict the actual proportions (calculated over both noise conditions) and are surrounded by 95% CIs (based on 10 000 bootstrap samples). The solid lines depict the probabilities predicted by the most parsimonious GLMM (Table TABLE I.), the light-gray lines illustrate the expected response for 500 simulated individuals (i.e., for each line, the random component of the intercept was drawn from a Normal distribution with mean = 0, SD = 0.542), the dashed lines represent the 2.5% and 97.5% quantiles of expected individual responses. The horizontal dotted line in all three panels depicts the expected (null) proportion of 0.5 in a two-choice test.