Happy H-owl-loween

October 2019

park ranger By Ranger Elizabeth

Screech owl perched on tree branch at night
Screech owl

As Halloween approaches, many of us start decorating and telling scary stories. One of the most common symbols associated with Halloween is owls.

Throughout the millennia, owls have been variously portrayed as specters of good and evil. Some African and Native-American cultures view owls as harbingers of death or messengers for the dead, while many Asian and Western cultures view owls as lucky, wise, and symbols of good fortune.

Biologically, however, owls are very important predators that help keep small mammal populations under control. Let’s look at some special owl adaptations that make such unique and successful predators.

Owl Adaptations

Eyesight

Four barn owls looking at camera
Barn owls

Owls have incredibly powerful eyes, with a visual sensitivity 35 times greater than our own. Some specialists say their eyesight may even be 100 times greater than ours. Some key things make an owl’s eyesight so much better than ours.

To start, for their size, owls have very large eyes. Owl eyes are so large they can’t move their eyes; instead, they must turn their whole head to look around. If our eyes were that big, they’d be the size of 6-inch dinner plates.

To help compensate for these very large eyes, owls have 14 neck vertebrae (we only have seven). This makes their necks extra flexible, allowing them to turn their heads at least 180°.

Why have these large eyes if you need extra neck bones just to look around? Well, larger eyes let in more light, which is critical for nocturnal hunters.

Owls also have more rods in their eyes (which help with black and white vision) than cones (which help with color vision).

Most importantly, owls also have a layer at the back of their eyes called the tapetum lucidum that reflects light back through the eye. This essentially doubles the amount of light available and gives them a yellow or green eyeshine.

Feathers

Another adaptation that owls have is unique feathers that enable them to fly in almost complete silence to sneak up on prey.

Owl feathers are coated in a velvety structure that helps absorb the sounds of wing movement. Their feathers are generally larger than those of other birds and have serrations along the edges to break up the turbulent air that can create a “swooshing” sound.

All these unique structures help reduce frequencies above 2 kHz, dropping the frequency of any sound below the typical hearing range of the owl’s typical prey.

Hearing

The hearing of an owl is very acute, partly because owls have asymmetrical ear placement: their ears are slightly offset from each other. This gives an owl the ability to perfectly pinpoint its prey.

An owl can determine the direction from which the sound is coming by the difference in time it takes for the sound waves to penetrate the right and left ears. Once the sound reaches both ears at the same time, the prey is directly in front of the owl.

One of the adaptations that allows owls to hear so well is the dense, tightly packed feathers behind their ears that helps cup the sound into their ears. Another adaptation is a facial disc of feathers that helps direct sound into the ears. Their sharp, triangular beak minimizes sound reflected away from the face.

Their ears are also specially tuned to the high-pitched frequencies emitted by squeaky rodents. A Great Gray Owl can pick up the tiny sounds made by a vole over 60 feet away, under 18 inches of snow.

Talons and Beak

Owls have very sharp talons and an equally sharp beak that make quick work of prey.

They use their talons to crush the skull of their prey and to knead the body so that it is easier to swallow. The strength of an owl’s talons varies by species, ranging from 5N of force produced by a Burrowing Owl to 130N of force produced by a Great Horned Owl.

The beak of an owl is short, curved, and downward facing, typically with a hooked tip to grip and tear prey for their young. The downward-facing beak keeps their field of vision clear and helps directs sound into the ears without deflecting sounds away from the face.

Diet

Rodents and other small mammals make up a large portion of an owl’s diet, but they will also eat insects, earthworms, fish, crayfish, amphibians, other birds, and small animals.

Owls will swallow their prey whole when possible, digesting the nourishing parts, and coughing up a pellet of indigestible parts. Biologists use these pellets to see exactly what owls are eating and to get valuable insight into predator-prey relationships.

Protecting Owls

A great way to help protect owls is by keeping your outdoor decorations minimal, and by taking down your decorations after the holiday. Put away any sporting nets after use, and make sure your fences are visible. Leave any old trees or sheds up for roosting or nesting owls, or you can put up a nest box.

Owls in Lockhart State Park

There are 11 species of owl in Texas, and you can see four of them in Lockhart State Park.

  • Barn Owl (Tyto alba): medium, pale-colored, long wings, short, squarish tail; head and upper body pale brown to grey; heart-shaped face is bright white
  • Barred Owl (Strix varia): large, greyish-brown; round head with no ear tufts; black eyes
  • Eastern Screech-owl (Megascops asio): usually greyish overall with ear tufts; yellow eyes
  • Great Horned Owl (Bubo virginianus): large, greyish-brown; white throat; large ear tufts; yellow eyes