Date: 3/16/17 7:11 pm From: Dan Gleason <dan-gleason...> Subject: [obol] Re: robin question
Robins, and other songbirds, do not have asymmetrical ears. Many owls locate moving prey by using sound more than relying upon vision completely. The asymmety of the ears assists with the ability to bettr locate the sound, especiallly as it is moving. It's worth noting that owls that hunt visually, like Pygmy-Owl or Flammulated Owls, show much less of this asymmetry.
When robins search for earthworms they do tilt their heads. This can help them listen more closely, much as we would turn one ear toward a source of sound we wish to hear better. Earthworms have a series of setea (bristles) along the length of the body. This helps them move up and down in their burrow. It is also why pulling an earthworm out of its burrow is not an easy task, for a robin or us. The setaa anchor it well and provide strong resistance. The action of these setea against the ground actually does poduce a sound. A robin, or other bird, can hear that sound when listening above the burrow. But, robins don't rely only on sound. By turning their head, they can also see more clearly down into that burrow and know that there is something there to feed upon. So sight and sound are both important, but asymmetrical ears would be of no greater use to locate this essentially stationary sound source.
Other birds foraging on lawns will also turn their heads to see or hear better what is below. Watch starlings do so. They often search for cranefly larvae by looking for their burrows The cranefly that chews the roots of your lawn is actually a European import. The larvae are just out of reach to most of our native birds. Starlings have muscles that open the beak more strongly than muscles to close the beak, as in most birds. So, the starling pokes its beak into a cranefly burrow and uses those strong muscles to open its mouth and expand the hole size, making the larva more easy to reach. (Despite our bias, starlings are not all bad.)
Owner, Wild Birds Unlimited of Eugene
Ornithology Instructor, University of Oregon
> On Mar 16, 2017, at 5:59 PM, <5hats...> wrote:
> Thinking about how robins tip their heads while listening for worms made me wonder. Are their ears asymmetrically placed on their head as those of owls are? Seems maybe like a question for Dan Gleason.