An analysis of the songs of most of the world’s passerine birds reveals that the frequency at which birds sing mostly depends on body size, but is also influenced by sexual selection. The new study from researchers of the Max Planck Institute for Ornithology and colleagues suggests that habitat characteristics do not affect song frequency, thereby refuting a long-standing theory.
Many animals use acoustic signals for communication. These signals have evolved to maximise the effectiveness of the transmission and reception of the sounds, because this helps finding a mate or avoiding predation. One of the fundamental characteristics of acoustic signals is the frequency of the sound. In forested habitats, acoustic signals become attenuated because of sound absorption and scattering from foliage, which is particularly problematic for high-frequency sounds. Hence, a theory from the 1970s predicts that animals living in habitats with dense vegetation emit lower-frequency sounds compared to those living in open areas.
A team of researchers led by Bart Kempenaers from the Max Planck Institute for Ornithology in Seewiesen and Tomáš Albrecht from the Charles University in Praha and the Czech Academy of Sciences analysed the variation in song frequency of more than 5.000 passerine bird species, encompassing 85% of all passerines and half of all avian taxa. PhD student Peter Mikula collected song recordings primarily from xeno-canto, a citizen science repository of bird vocalisations, and from the Macaulay Library of the Cornell Lab of Ornithology. MORE
Header image: A global study of songbirds like this field warbler shows that song frequencies primarily depend on body size. Credit: © Tomáš Albrecht.