Asked by: Janine Kay, by email
Humans can hear frequencies up to about 20kHz, whereas dogs hear up to 45kHz. Almost all mammals have much better high-frequency hearing than other vertebrates - fish, amphibians and reptiles only hear up to about 5kHz, and birds up to 8-12kHz.
It's not that mammals need high-frequency hearing for communication - most can hear frequencies well above the ones they make themselves. Instead, mammals have adapted in this unique way so they can locate where a sound is coming from. Called 'binaural spectral-difference cueing', their special way of hearing works by comparing the frequency range of a sound as it arrives in each ear. Because the ear on the farthest side is partially 'shadowed' by the head, some of the frequencies will be absorbed - higher frequencies are absorbed more than lower ones.
But the smaller the head, the less effect it has on lower frequency sounds, so the animal must be able to hear a higher upper frequency limit in order to be able to detect the spectral-difference effect. A mouse needs to hear up to 90kHz to use binaural spectral-difference cues, whereas an elephant manages with just 10kHz. Dogs fall somewhere in the middle because they have smaller heads than us.
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