Mammalian ear specializations in arid habitats: structural and functional evidence from sand cat (Felis margarita)

To test whether structural specializations of sand-cat ears are adaptations to their desert habitats we measured structural and acoustic features of their ears. The area of the external ear's pinna flange is similar to that of domestic cat. The dimensions of the ear canal are about twice domestic cat's, as is the volume of the middle-ear air space. The magnitude of the acoustic input-admittance at the tympanic membrane is about five times larger than that of domestic cat; both the middle-ear cavities and the ossicular chain contribute to the increase. Structure-based models suggest the acoustic admittance looking outward through the external ear is generally larger for sand cat than for domestic cat; the radiation power-efficiency is also larger in sand cat for frequencies below 2 kHz. Hearing sensitivity (estimated from measurements and model calculations) in sand cat is predicted to be about 8 dB greater than in domestic cat for frequencies below 2 kHz. Analysis of attenuation of sound in deserts implies that the increased sensitivity extends sand cat's hearing range beyond domestic cat by 0.4 km at 0.5 kHz. Thus, the structural specializations may provide habitat-specific survival value.