Body size shapes song in honeyeaters

Abstract

Birdsongs are among the most distinctive animal signals. Their evolution is thought to be shaped simultaneously by habitat structure and by the constraints of morphology. Habitat structure affects song transmission and detectability, thus influencing song (the acoustic adaptation hypothesis), while body size and beak size and shape necessarily constrain song characteristics (the morphological constraint hypothesis). Yet, support for the acoustic adaptation and morphological constraint hypotheses remains equivocal, and their simultaneous examination is infrequent. Using a phenotypically diverse Australasian bird clade, the honeyeaters (Aves: Meliphagidae), we jointly examine predictions of these two hypotheses. We find that body size constrains song frequency and pace in honeyeaters, while beak shape constrains the rate of song pace evolution. Although habitat type and environmental temperature influence aspects of song, that influence is indirect, via effects of environmental variation on body size. Our results demonstrate that morphology has an overwhelming influence on birdsong, in support of the morphological constraint hypothesis, with the environment playing a secondary role generally via body size rather than habitat structure. These results suggest that changing body size, a consequence of both global effects such as climate change, and local effects such as habitat transformation, will substantially influence the nature of birdsong.

Song evolution and diversification patterns are uncorrelated in honeyeaters

“…This is likely driven by allometric constraints imposed by body size (Fletcher 2004), which itself is a very conserved trait, and directly impacts the length of the vocal tract and the size of the syrinx (Bertelli and Tubaro 2002;Suthers and Zollinger 2008). Certainly, body size has been demonstrated to have a prominent influence on honeyeater song and has been found to structure variation in frequency and song pace (Hay et al 2023). Interestingly, minimum frequency was found to have the highest phylogenetic signal rather than peak frequency.…”

“…However, past studies have shown that small range sizes resulting from dispersal to islands has been a primary driver of speciation in these clades (Hay et al 2022), and the (non-significant) slight increase in speciation rate observed with these shifts in song evolution could be due to these underlying factors. It is also important to consider the influence of body size on these patterns because honeyeater song is under strong allometric constraints (Hay et al 2023), and these clades show great differences in body size.…”

“…We use a song dataset from a previous honeyeater study (Hay et al 2023). Containing song data for 163 honeyeater species, the song dataset considers five relevant aspects of song (Fig.…”