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Figure S2 from Character displacement of a learned behaviour and its implications for ecological speciation

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journal contribution
posted on 17.07.2019 by Cody K. Porter, Craig W. Benkman
Spectrograms of contact calls from three individual crossbills that produced Cassia crossbill contact calls when first recorded but switched to producing ponderosa pine crossbill calls in subsequent years (note that we detected no call switching between Cassia and lodgepole pine crossbills, consistent with their greater divergence in call structure). The sex and identification number of each bird is listed at the top of each spectrogram, with the recording dates below. The key feature distinguishing Cassia crossbill contact calls from ponderosa pine crossbill contact calls is the presence of an initially ascending element to the call, which is initially descending in ponderosa pine crossbill calls, though the calls of these crossbills also differ in a variety of frequency characteristics (e.g., fundamental frequency and frequency modulation).