For the Birds Radio Program: Presbyopic Owls and Aging Waxwings
Laura talks about some adaptations birds have that she wishes she did.
I was reading through an avian physiology book recently, studying up on bird vision, when I came upon this interesting sentence: “Predatory birds such as owls have long, tubular eyes shaped to act like telephoto lenses and cannot readily accommodate their eyes to focus on very near prey. Owls are thus sometimes forced to back away from wounded or dead prey to better see the animal before attacking or eating it.”
This is the kind of interesting trivia I normally file away in my brain for future reference, but reading this one got me pondering about more immediate implications. I’ve long assumed that owls have very long wings relative to their body weight because that allows them to carry heavy prey in addition to their own body weight. And the longer wings allow slower flapping, which allows more silent flight. But suddenly I’m wondering whether those long wings aren’t really an adaptation allowing owls to hold their restaurant menus farther out.
If the avian eye is so well adapted that it acts as quality binoculars as well as the highest corrective lens, why couldn’t it have developed to serve as bifocals as well? Of course, if l were ever to imagine a bird wearing bifocals, it would certainly be an owl, but that comes from watching too many Disney movies, wherein owls always seem to personify cranky or wise men old enough to suffer from presbyopia. Suddenly I’m gratified to learn that my own sudden inability to focus on near things unless I take off my glasses isn’t because I’m in my 40s-it’s because I’m growing more owl-like every day.
At my age, another bird that is suddenly very appealing is the Cedar Waxwing, which gets its name from the tiny dots of red on the tips of some of its secondary wing feathers. These brilliant red drops reminded an early ornithologist of drops of sealing wax.
More recent ornithologists have learned that the number of red feather tips is correlated with the age of each bird, and that waxwings use these feather tips to recognize which potential mates are older and more experienced. With waxwings, the older you are, the more desirable you are to the opposite sex. As I perch here on this side of 40, that seems rather a fine approach to life. And of course, waxwings don’t have to worry about holding things out from their faces to see close up, which seems rather a fine approach to middle age, too. Most songbirds have rather flat eyes compared with humans, designed for precise close focusing, and many species can even make adjustments with their corneas as well as their lens for accommodation between distant and near vision.
Owls don’t seem to mind their far-sightedness, waxwings age gracefully–it’s only us humans who gripe about getting older and pay billions of dollars annually for magic potions to stop the clock. It’s the bird inside that clock that has the last laugh.