A nose that roars: anatomical specializations and behavioural features of rutting male saiga.

The involvement of the unique saiga nose in vocal production has been neglected so far. Rutting male saigas produce loud nasal roars. Prior to roaring, they tense and extend their noses in a highly stereotypic manner. This change of nose configuration includes dorsal folding and convex curving of the nasal vestibulum and is maintained until the roar ends. Red and fallow deer males that orally roar achieve a temporary increase of vocal tract length (vtl) by larynx retraction. Saiga males attain a similar effect by pulling their flexible nasal vestibulum rostrally, allowing for a temporary elongation of the nasal vocal tract by about 20%. Decrease of formant frequencies and formant dispersion, as acoustic effects of an increase of vtl, are assumed to convey important information on the quality of a dominant male to conspecifics, e.g. on body size and fighting ability. Nasal roaring in saiga may equally serve to deter rival males and to attract females. Anatomical constraints might have set a limit to the rostral pulling of the nasal vestibulum. It seems likely that the sexual dimorphism of the saiga nose was induced by sexual selection. Adult males of many mammalian species, after sniffing or licking female urine or genital secretions, raise their head and strongly retract their upper lip and small nasal vestibulum while inhalating orally. This flehmen behaviour is assumed to promote transport of non-volatile substances via the incisive ducts into the vomeronasal organs for pheromone detection. The flehmen aspect in saiga involves the extensive flexible walls of the greatly enlarged nasal vestibulum and is characterized by a distinctly concave configuration of the nose region, the reverse of that observed in nasal roaring. A step-by-step model for the gradual evolution of the saiga nose is presented here.