Over the past months, I’ve periodically covered the strange extravagance of birds in various dimensions: the fastest birds, the biggest birds and the smallest birds, for instance. Considering the extremes is always interesting; it inoculates us against viewing the world as essentially boring and mundane. And there is another multifaceted way in which birds exceed our standard human frames of reference and appear like strange and extraordinary creatures: in the sharpness of their senses, whether of hearing, sight or even smell.
Consider hearing first. Perhaps the most striking example of birds’ sensitive hearing is the case of owls. While they do not truly echolocate (though a few bird species like oilbirds and swiftlets do), owls do rely on their sharp hearing to detect their prey. Imagine the great horned owl you can hearing hooting outside your window. Perched in a neighborhood tree or even on your house, they spend their evenings listening. A mouse squeaks a few yards over or quietly gnaws at a hard food item somewhere down below and the owl’s head swivels round — its next meal has been found.
I can’t help but make a small aside that enhances the impressiveness of owl hearing even more: they can listen so acutely in part because their own movements are so quiet. Owls have special velvety feathers that enable silent flight and surround their ear cavities with wind-dampening fluff like the microphones used by outdoor filming crews. Electric cars are quieter than gas engines, and a bike makes the electric car seem loud, but an owl makes all human existence sound noisy and clumsy in the extreme. Owls can hear their moving prey even as they fly, gliding silently through the night ready to detect the breaking of a brittle leaf.
Turkey vultures have a sharper sense of smell than any of our other birds. (Photo by Allan Hack)
The eyesight of birds can likewise far exceed our human capabilities. Owls again provide an initial example. They are famously large-eyed, with most cartoon caricatures practically defining them by the largeness of their eyes. This is true: human eyes weigh about 1% of our skull weight, while owl eyes can add up to nearly a third of the weight of their skulls. These are physically more capable instruments. What we would consider impenetrable, moonless darkness is probably more like a landscape illuminated by a glaring full moon to an owl. When a full moon is shining and we consider the evening relatively bright, the world might appear to them as clear as our normal daytime world.
But the impressiveness of bird vision is not limited to owls. The same mandate of prey detection drives the extreme development of eyesight seen in many other predators. The birds of prey are famously sharp-sighted — “eagle-eyed” we call those who see superbly well. But where owls have evolved to overcome darkness, the diurnal raptors excel at overcoming distance, the second great limit to our vision. Consider a red-tailed hawk, watching from high up in some tree or tower, or soaring somewhere higher, beyond the limit of our structures. They will hunt from such locations, watching the ground below for the movement of a squirrel or snake, ready to strike and to descend upon a crawling creature a football field away. Nor are predators limited to the large: bluebirds, phoebes and other insect-catching flycatchers do something quite similar on a smaller scale, pouncing on insects whose existence is to us invisible.
The final of the major senses: smell. For humans, the sense of smell is a crude and imprecise tool. We know that dogs can follow scent trails that are utterly invisible to us. There is a bird that exceeds our olfactory abilities with a similar magnitude: the turkey vulture. While most birds have only weak senses of smell and find their food by sight, our common vulture can detect entirely invisible carcasses while flying by hundreds of feet in the air. One notable study concealed 24 chicken carcasses under a forest canopy, burying them under leaves to render them entirely invisible from above. Within a day, turkey vultures had found 23 of them.
A quiet mouse, a tiny insect or even the silent and unmoving remnants of a chicken — all of these are things we miss, but all of them are clear to birds.
Jack Gedney’s On the Wing runs every other Monday. He is a co-owner of Wild Birds Unlimited in Novato and author of “The Private Lives of Public Birds.” You can reach him at jack@natureinnovato.com.