The ears of the birds

When most people think of bird senses, they think of the eyes. Sayings like “eagle eye” and “bird’s eye view” come to mind. And it is true, the primary sensory organ that birds depend upon to survive is their eyes. However, hearing is the second most important sense, and is also crucial to the bird’s well-being. Birds use their hearing during mating rituals, to recognize threats, to communicate their location and, in some species, to capture their prey.

Structure

Birds don’t have outer ears like humans, but otherwise the anatomy is quite similar, containing an inner and middle ear. Our external ear is replaced on birds by a funnel-shaped opening on each side of the head. This opening is protected by soft, barbless feathers called auriculars. The auriculars also help to reduce wind noise.

Birds hear better than humans — a useful adaptation when your life depends on it! The left and right ears differ slightly in both frequency response and location. The difference in frequency between the ears allows birds to better locate the origin of sounds. In owls one ear is located slightly lower than the other; this asymmetrical positioning means that sounds do not hit their ears at the same time. This minute difference in timing (millionths of a second) allows birds to triangulate the source of a sound.

Uses

If you’ve ever been woken by a Northern Mockingbird in the middle of the night, you know that during the spring, many birds sing during the mating season. Songs are used to demarcate territories and attract females. Often, it is the best singer who wins the mate. And of course, females need to be able to hear these songs for the males to be successful. During all seasons birds call to one another with chips, clucks, and song snippets to advertise their position, and sometimes warn of danger. Again, hearing is an essential part of this communication process.

Owls use their highly sensitive ears to pick up the faintest of sounds, like a mouse tunneling beneath a layer of snow (which might be several feet thick), in order to precisely dive down and snatch it with their talons. And a few species, like the oilbirds of South America, even use their ears for echolocation (like bats) to make their way through dark caves and nightly forays though the jungles.

Current regional sightings

A number of sparrows are calling the Burning Star Mine (Jackson County) their winter home, including Fox, Savannah, American Tree and Swamp Sparrows. And two Short-eared Owls were also spotted there on Dec 11. Twenty-two Trumpeter Swans were spotted close to Richview in Jefferson County, and 28 were close to Royalton in Franklin County. Flocks of Bonaparte’s Gulls have been seen at Carbondale Reservoir and Crab Orchard Lake. A Loggerhead Shrike continues at the Denmark Unit of Pyramid SRA. At least one of the Whooping Cranes had returned to Kaskaskia Island as of Dec. 10.

If you’re looking for additional ideas about where to go birding in southern Illinois, please consider my book, "Finding Birds in Southern Illinois," available in print or PDF at www.southwestbirders.com.

• Henry Detwiler spent an exciting 16 years as a bird guide and has penned bird-finding books for several Arizona, California and Illinois counties. You can reach him at henry_detwiler@yahoo.com.