No support for honest signalling of male quality in zebra finch song

Alam et al.1 claim to have discovered a song feature, called “path length”, that honestly signals male fitness and is therefore preferred by all females. We see no statistical support for this claim in the original data. (1) The main finding about path length being an honest signal of quality (Fig. 4c) results from a statistical artefact, the regression of y minus x over x, which creates an illusory effect where none exists. (2) The low technical repeatability of path length measure further questions its use as a proxy of male quality. Consequently, the conclusion that females generally prefer songs with long path lengths in playback experiments is unconvincing and also inconsistent with general knowledge about mate choice in the studied species2-6.