Can beak size affect the acoustic frequecies in the woodcreepers (Dendrocolaptinae)?

PALACIOS, M. G.; TUBARO, P. L.

Ithaca, New York, EEUU

Congreso; 117th meeting of the American Ornithologists’ Union; 1999

American Ornithologists’ Union

Woodcreepers conform a monophyletic group endemic of the Neotropical region. It includes about 50 species showing strong differences in beak size and shape. We assessed the effect of beak morphology on the acoustic structure of their songs using a comparative analysis of independent contrasts. This analysis was based on the phylogeny of Raikow (1994) and the tape-recordings of Hardy et al. (1994). On each species we measured the maximum and minimum frequencies (MAX and MIN, respectively), the bandwidth (MAX – MIN) and the emphasized frequency (ENF) of their songs. The residuals of variation in beak length and acoustic frequencies (after discounting the effect of body size and phylogeny) were calculated for each species and compared. We found a negative and significant relationship between residuals of MIN, ENF, and residuals of beak length. In other words, within each pair of species compared, the one with the longest beak had the lowest frequencies in its song. This result is compatible with the idea that the vocal tract (cranial to the syrinx) has resonating properties that affect the frequency spectrum of the song.