Astute Avian Eyes

Birds' eyes are their dominant sense organ. They can hear quite well and some birds even smell well, but their sense of vision triumphs. In fact, their eyes are so large for the size of their heads that there's no room left for muscles to rotate them. They must cock their heads from side to side, in order to cover a decent field of view.

So visual acuity is definitely a bird's strong point. They can see two to three times more sharply than humans. The color and detail receptors in a bird's eye—called cones—are two to three times greater in number than for us. (That's something like 15 million cones, in a much smaller eye!) Their visual acuity leaves us far behind.

I recently watched a titmouse at the bird feeder—extracting and then rejecting at least 10-15 sunflower seeds, before becoming satisfied enough to fly off with a choice seed and commence to grasp it in its feet and bang away with its beak, to get at the sweet nut within. Most titmice (as well as their close cousins the chickadees) will fly to the feeder, quickly grab the first seed they can, and fly away to work at it. Why was this particular titmouse being so finicky—tossing away rejected seeds, until it found just the right one?

The surface of the feeder tray is strewn with hundreds of sunflower seeds and empty hulls—the latter being far dominant. When I look at the tray (to see if it's time to replenish seeds) I tend to think that there are plenty of them available, so I sometimes delay restocking the container. If I take a closer look, however (by taking the time to put my glasses on), I can usually see that most of them are empty husks. I have to look closely to determine this, yet I watch one of these birds fly to the platform, instantaneously grab a seed from all the empty hulls, and fly away to get at its interior morsel. Such keen eyesight! Their astute sense of vision is also demonstrated when I watch one of them dart to a tree trunk and pluck a tiny, juicy bug from a tiny crack.

Back to the picky titmouse who rejected a dozen or more seeds, before finally flying off with one: I'm assuming that it was looking for a fat seed, that promised a particularly large interior nut. If so, it was demonstrating an enhanced ability over its buddies, to be choosy and find that fat seed.

Why is only this one bird being so choosy? I've seen him do this trick before. While all the other titmice flit down and quickly grab a seed, this guy takes his time. Has he learned something that the others have not? Is his eyesight simply less astute? Another fascinating observation may be leading me towards one more step into the lives of these local birds.