Cross-correlation analyses of a series of downswept calls. Cross-correlation analyses of a series of downswept calls. A series of nine D calls are numbered in red on the audio spectrogram (256-point FFT, Hamming window, 99% overlap). Of these nine calls, eight register a concurrent accelerometer signal on at least one of the tag's orthogonal axes (three lower panels). Only call 3 registered no detectable acceleration signals. Red asterisks indicate acceleration signals that yielded peak coefficients of at least 0.25 when cross-correlated with aligned audio signals. Below the accelerometer spectrograms, the acceleration vectors of all nine calls were cross-correlated with one another. Cross-correlation functions for all three axes are shown in the same plots, with x-axis functions in magenta, y-axis functions in green, and z-axis functions in blue. Normalized cross-correlation coefficients are displayed in red for pairs of signals that were highly (≥0.25) correlated along all three axes. The red boxes indicate that calls 5 to 9 all have highly correlated acceleration signatures, which suggests that they were produced by the tagged whale. There were no significant correlations among the acceleration signals of calls 1 to 4, suggesting that they were produced by another whale (or whales) whose orientation relative to the DTAG was not fixed. Mark R. Saddler et al. J Exp Biol 2017;220:4119-4129 © 2017. Published by The Company of Biologists Ltd