Sunday, January 24, 2010
Whatever Gets You Through the Night...If You Are An Owl, That Is!
Contrasting with our winter waterfowl walk, we were not quite so fortunate with the species count during our evening owl prowl, in fact, despite our heroic efforts (and hopes) the owls were not to be found. Participants might not have seen any wild owls, but they were treated to a program given by John Turner and myself on the natural history of LI owls, including what they eat, how they hunt and their amazing adaptations to nocturnal life. John spoke about the various owls that call LI home (temporary and permanently) and I spoke about what makes an owl so well adapted to the night life. Here are some cool facts that I thought might interest readers.
Of course, not all owls are strictly nocturnal. Some, such as the short eared and great gray are crepuscular (meaning they are active at dawn and dusk, although the great grey will also hunt during the day). Others, such as the snowy, are partly diurnal (active during the day), while some are mainly diurnal (northern hawk owl).
Many people believe that owls can see in complete darkness. Not true. They are just as blind as you and me in a completely blackened room. How do they see at night then? Well, think about it. The night sky is never completely dark. Not really. Owls possess a remarkable ability to utilize even the smallest amount of light due to an abundance of rods in their eyes. There are two types of photoreceptors in the eye: Cones, which are related to color vision, and rods, which are related to the ability to see in dim light. Owls have 10x as many rods as humans do. Check this out: if a match stick was lit in a football stadium, not only would an owl see it, that tiny flicker of light would provide enough light for successful hunting! Owls also have huge eyes, which account for 1-5% of their body weight. In fact, the eyes are so huge that they are elongated, rather than round. These tubes are held into place by bony structures called sclerotic rings. This is why an owl cannot move its eyeballs. Thanks to its 14 vertebrae (to our 7) an owl can move its head 270 degrees, lightning fast, 3/4 of the way this way, 3/4 of the way that way, and almost upside down, thus making up for this lack of peripheral vision.
Now, what is not a myth is that owls CAN hunt and catch prey in complete darkness. Wait, didn't I just say that it is a myth owls can see in complete darkness? How can this be then? Well, I didn't say they couldn't HUNT in complete darkness! Because they do not need to SEE to hunt. Their hearing ability is astounding. The ears are located at the side of the head, behind the eyes and are covered by feathers. Most owls have asymmetrical openings. The feathered facial disc acts like a radar, guiding sounds into the owl's ears. When a sound is detected, the owl is able to tell from what direction it is coming in an instant. If a sound is coming from the left of the owl, the left ear will pick up on it first. The owl will turn its head until it can hear the sound simultaneously in both ears. At that point it knows whatever is causing the sound is directly in front of it. Owls can detect a left/right time difference of 30 millionths (!!!!) of a second. They can also tell if the sound is higher or lower, thanks to those asymmetrical ear openings.
The owl's brain processes this melding of left, right, up and down in an instant, which then pinpoints with deadly accuracy where the sound is coming from. Once the bird has determined the location of its victim, it flies towards it, always keeping in direct line, adjusting midflight if the prey moves in order to keep the prey within the mark. Thanks to their astonishing hearing, owls are also able to strike prey that is buried under snow or leaf litter, without ever seeing it. Incredible!!!
You have to admit, owls are pretty cool to look at, but when you understand the adaptations that make an owl an owl, you understand just how amazing these birds of prey truly are!