During these warmer months we cool our home naturally by opening the windows at night to let in the clear, clean air. Lying in bed with refreshing zephyrs gently flowing over us, we often sense evidence of another world, the nocturnal world, operating out there in the dark. A good example is the occasional faint aroma of the lady skunk who lives in our culvert, as she marches out, tail erect, to see what’s for dinner that night. But there’s much more.
In our rural subdivision not all the nighttime sounds are human. Coyote howls from near and far often reach our ears as those very social animals communicate with other members of their pack. The call of the wild! Then there’s the equally enchanting but very soft “who-hoo whooo” of the great horned owl (Bubo virginianas) as he probes the darkness for a mate or announces his territory to other owls. While humans are fairly new on the evolutionary scene, great horned owls go back millions of years and have adapted efficiently to survive in various, often changing environments. They can be seen from Amazon jungle trees to Alaskan church steeples. What makes this species and other owls so remarkable Is the evolution their vision and hearing have undergone to make them better hunters.
That evolution has been very effective: great horned owls are superb night hunters. Their eyes are as large as ours and much more sensitive. Unlike most birds their eyes are cylindrical and locked straight forward, but they can rotate their heads more than 180 degrees to see the whole world. The eyes themselves, unlike ours, are made up mostly of light-sensitive rod cells rather than cones. They can’t see the colors we can, but they can detect a mouse in the dark with only five percent of the light we would need. On the other hand, owls are often seen squinting in daylight and they avoid bright lights at night, which some people use to protect their chickens and pets.
Even more evolved for hunting is their hearing. Most owls have faces shaped like hearts or satellite dishes so that sound is reflected toward their ears, enabling them to hear better. Their very short, non-protruding beaks, along with the ability to adjust the feathers around their ears, also help them capture more sound. Over the millennia the ear holes in their skulls have become asymmetrical, one much higher than the other, so that arriving sounds can be triangulated to determine position. It’s estimated that there’s a difference of about 200 microseconds between the times the sound reaches each ear. The owl’s brain is able to process that difference, combine it with information from the eyes, and zero in on the quarry in total blackness. Add to these useful sensory capabilities that owl feathers are very soft and downy at their ends. This allows them to swoop down on their prey in almost total silence. Sorry, Mr. Mouse!
When an owl eats something like a mouse, his stomach acids won’t digest the skin, bones or teeth, instead they’re formed into a thumb-sized pellet in the owl’s gizzard. That pellet is then slime-coated to make it easily coughed up and ejected. I once knew some kids at a country school who made a modest income finding fresh owl pellets under a row of cypress trees near the school and selling them to a biological supply house. They were then shipped to schools all over the country for dissection classes. Today even Amazon sells barn-owl pellets, which are more likely to contain mouse remains than those of great horned owls. They offer various quantities from one to thirty pellets at about five dollars each, and usually enclose a bone diagram so that students can dissolve the pellets and reconstruct the mousy skeletons on their worktable.
If it weren’t for predators like owls, coyotes and others, we would soon be inundated, in true Malthusian fashion, with hordes of rodents, insects and other small species that have evolved to proliferate. These hunters make our lives easier by limiting those populations and maintaining Nature’s balance. We should admire them for that. Thank you, owls and others!
