JEB -- Nelson et al. 208 (2): 297 Figure IG5

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Fig. 5. Vocal tract resonances do not vary with beak gape below $~$ 4 kHz. Instead decreases in beak gape attenuate sound frequencies between $~$ 4 and 7.5 kHz. (A) Spectra obtained for different beak gapes plotted relative to a spectrum obtained with a maximum beak gape (11 mm). (B) Standard deviations (S.D.) calculated across spectra displayed in A.