“…Given the compelling evidence that sperm competition acts concurrently on sperm morphology in a directional and stabilizing manner, recent studies have used mean sperm length and the coefficients of variation of sperm length, both within and between males, as proxies of the intensity of sperm competition (Omotoriogun, Laskemoen, et al, ; Sardell & DuVal, ). These studies have been taxonomically restricted to passerine birds (Albrecht et al, ; Calhim et al, ; Immler et al, ; Kleven et al, ; Lifjeld et al, ; Lüpold Linz & Birkhead, ; Lüpold, Linz, Rivers, et al, ; Omotoriogun, Albrecht, et al, ; Omotoriogun, Laskemoen, et al, ; Sardell & DuVal, ), with the exception of one study on shorebirds (Johnson & Briskie, ) and one on pheasants (Immler et al, ), though the latter found no effect of sperm competition on sperm morphology. Most studies focused on temperate zone species (Calhim et al, ; Immler et al, ; Kleven et al, ; Lifjeld et al, ; but see Albrecht et al, ; Omotoriogun, Albrecht, et al, ; Omotoriogun, Laskemoen, et al, ).…”