Given the extent to which birds rely on vocalisation and how much effort has gone into the study of their calls and songs, it is remarkable how little we still know about their hearing. I wonder whether this lack of interest is partly a consequence of birds having no external ear or pinna, which is part of their reptilian heritage.We know that birds can hear an almost identical range of sounds to us. They achieve this with a single middle ear bone, rather than the three we have - again a product of their reptilian ancestry. Intriguingly, the hearing ability of birds living in temperate climes fluctuates through the year. The auditory regions of their brains grow during the breeding season, then shrink when song becomes less important. Understanding this process could provide clues to treating Alzheimer's and other neurodegenerative diseases.
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