The acoustical effect of the neck frill of the frill-necked lizard (Chlamydosaurus kingii)

Abstract

Animals localise sound by making use of acoustical cues resulting from space and frequency dependent filtering of sound by the head and body. Sound arrives at each ear at different times, with different intensities, and with varying spectral content, all of which are affected by the animal's head and the relative sound source position. Location cues in mammals benefit from structures (pinnae) that modify these cues and provide information that helps resolve the cone of confusion and provide cues to sound source elevation. Animals without pinnae must rely on other mechanisms to solve localisation problems. Most non-mammals lack pinna-like structures, but some possess other anatomical features that could influence hearing. One such animal is the frill-necked lizard ( Chlamydosaurus kingii). The species' elaborate neck frill has been speculated to act as an aid to hearing, but no acoustical measurements have been reported. In this study, we characterise the frill's influence on the acoustical information available to the animal. Results suggest that the change in binaural cues is not sufficiently large to impact localisation behavior within the species' likely audiometric range; however, the frill does increase gain for sounds directly in front of the animal similar to a directional microphone.

Hearing ability of prairie voles (Microtus ochrogaster)

“…Our HRTF results suggest prairie voles have ITD sensitivity consistent with their head and pinna sizes (∼± 80 μ s, calculated as pinna width plus inter pinna distance divided by the speed of sound, 343 m/s). The general slope and range of cues match well with the expected ranges based on their head features and are consistent with similar measurements in other species (human, 34,53,54 cat, 55–57 monkey, 58,59 ferret, 60,61 tammar wallaby, 62 various species of bats, 63–66 gerbil, 41 chinchilla, 67,68 mouse, 69,70 rat, 71,72 rabbit, 73 barn owl, 74,75 guinea pig, 33 and frilled neck lizard, 35 among others). Unsurprisingly, as pinna and head size were similar between the sexes, HRTF measurements did not show clear differences between the sexes.…”