Birds’ songs and calls are important for survival. The ear of a bird is very much like that of a mammal’s with two important exceptions. The external ear lacks a pinna (the flesh-covered outer ear) although owls have one, and nstead of three vibration-transmitting bones birds have only one, the columella. When sound waves hit the eardrum they are transmitted to the columella and then the cochlea, the fluid-filled organ that contains hair cell nerve endings. The hair cells move in the cochlear fluid and transmit information to the brain. Unlike us, whose hearing declines with age and exposure to loud noises that cause the death of hair cells, avian hair cells continually regenerate so birds maintain their hearing all of their lives.
The hearing range of most birds varies from 1000-4000 Hz; humans hear between 20-20,000 Hz (Hertz, a measure of frequency). The range differs among bird species. The Horned Lark hears between 350 and 7600 Hz, the Canary from 1100 to 10,000, the House Sparrow from 675 to 11,500 Hz and the Long-eared Owl from 100 to 18,000 Hz. Even though the frequencies at which birds and humans hear best are similar, birds are more sensitive to the tone and rhythm of sound so they can more easily discern sounds even in a noisy environment.
We cannot see the ear opening of birds except for those with unfeathered heads such as vultures and storks. In most birds this hole is covered by feathers that protect the ear from air rushing over it and help to funnel sounds into the ears as the bird flies.
Most birds determine the source of a sound by moving their head, like we do. Watch an American Robin or European Blackbird walking along the ground with its head turned toward the soil; some say that the birds are listening for worms or insects crawling in their burrows or under the litter. In reality they are simply looking for worm castings or other signs of prey. Some woodpeckers, though, have the ability to hear beetle larvae crawling under the bark of a tree.
Nocturnal birds depend more on sound even though their night vision is excellent. Barn Owls have a flattish facial disk that funnels sounds toward the ears and fleshy ears not unlike humans’, but asymmetrical in shape and location – they don’t look exactly alike, and one is higher on the head than the other. Sometimes, when I give a talk on birds I ask for a volunteer in the audience to help explain why owls can locate sounds better than us. I ask the volunteer to close her eyes and tell her I will snap my fingers in front of, over, or behind her head and that it is her job to determine the direction of the sound. Since I snap my fingers in the vertical plane that bisects her head from front to back, the volunteer rarely guesses correctly because the sound hits both ears with the same frequency and volume. (Once I unknowingly chose a blind person, who, as expected, got it right. I will never again assume blind people do not attend illustrated lectures.)
Research to find out how to regenerate human sensory hair cells in our ears is ongoing. Maybe hearing aids will become a thing of the past, thanks to birds.