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“There are owls in those trees!” Lower Falls of Yellowstone Falls, Yellowstone, Montana

On Silent Wings, Owls

I love owls! Owls get me thinking about the natural selection that must have taken place for a bird to be a successful nighttime predator. From an evolutionary standpoint, it makes sense that a bird would evolve to fill the niche of flying nighttime predator. It’s the steps to getting there that fascinate me. What do you think came first silent flight, superior hearing, or the ability to see well in the dark?

The parks we have stayed in had ranger talks every night. The owl talk at Yellowstone National Park was an excellent one. I took notes so I could share the information with you.

Adaptations of a Flying Nocturnal Predator

Hearing
Nighttime is dark! It is essential that nocturnal predators have excellent hearing so they can hear prey, like mice and chipmunks, move. Owls have several adaptations that give them superior hearing abilities.

  1. Face shape: Owl faces are concave, bowl shaped. This funnels sounds to their ears.
  2. Placement and shape of their ears: Owl ears are flush with their skull, placed just at the top lip of the “bowl”, and offset from each other. Having their ears flush with their skull and at the lip of where sound funnels give owls superior hearing ability. Owl ears are offset from each other, with one being slightly higher on their skull. This helps owls determine the vertical direction, above or below, a sound comes from. For example, if the sound comes from above them, the ear that is higher on their skull will hear the sound first.
  3. Owls can independently move each of the muscles in their face. This helps them move their ears to better determine the direction sound comes from.
  4. Beak location: Bird beaks are analogous to your nose and mouth. An owls’ beak is very low on its face so it doesn’t interfere with the quality of sound as it is funneled to its ears. You nose and mouth would be on your chin if it were placed in a similar location to an owls.

Sight
Owls do not just rely on their sense of hearing. They also have superior nighttime vision.

  1. An owls’ eyes take up 70% of its face. That is a lot of face space dedicated to the sense of sight.
  2. Owls have 3 types of eyelid. One is similar to ours. It is for blinking and sweeping debris from the eye. This eyelid closes down. The second eyelid is fur covered (not feather covered – I was surprised by that). This eyelid closes up and it is the eyelid that allows owls to sleep soundly during the day. It functions similarly to a blackout curtain. The third eyelid is a nictating membrane that closes from the inside corner of the eye outward. This membrane is common in many animals, including dogs. It is a clear membrane that gives protection to the eye when moving, like when an owl swoops down through tree branches to catch a mouse. It protects the eye if pine needle brush then net part of the eye.
  3. In the back of the eyes of animals are sight receptors called rods and cones. Cones are important for seeing colors, and rods are important for seeing white, black, and shades of gray. People have an equal ratio of rods to cones. Nocturnal animals do not need to see colors well. Next time you are up late sit outside and think about how much color you see even with all the cones in your eyes. Most of what you see will be in shades of white and black. Owls have many more rods than cones. It has been determined that because of this adaptation they see about 20% better at night than people do.
  4. An owl’s eyes are fixed to their skull. In contrast, you are able to move your eyes in your eye sockets. To compensate for the inability to move their eyes in their eye sockets owls have 14 neck bones (people have 7) so that they can rotate their heads 270 degrees and up and down. This extends their range of sight and hearing.

Silent flight
Perhaps the coolest adaptation owls have is silent flight! Sound travels through the air in waves. Sound waves are heard when the waves reach a target such as an ear. The larger the wave, the louder the sound. If the waves are disrupted, they do not reach the target as sound. The tips of an owl’s flight feathers are tapered and feathered in cone-like fashion in such a way that the tips cut through the sound waves that are generated by the force of motion of the owl’s wings as they fly. By cutting through the sound waves, the waves are nullified and there is no sound wave to be heard. Sit outside at night and listen to how quiet it is. Silent flight is important for catching prey at night.

Catching prey
Have you ever felt a cat’s tongue? That is what the skin on owl feet feels like. An owl’s talons are similar in feel to a cat’s claws. Needle-like talons and raspy feet help owls grab their furry prey without losing hold and ending up with nothing but a talon full of fur.

Better survival of all babies hatched not just the “fittest”
Most birds lay all the eggs in each clutch, litter, one after the other at the same time. The eggs hatch at the same time too. The babies are in direct competition with each other, because they all have the same care requirements, with the largest and/or loudest being fed first and most. This results in a better chance of living to adulthood for the loudest and largest of the chicks born.

Owls use a different hatching strategy. Over the course of a month, owls lay three eggs. The laying of each egg is spaced 7 to 10 days apart from when the other eggs are laid. This makes more work for the parents, but it increases the chance of survival of each chick because the babies are not in direct competition with each other. The parents work together to care for the babies. The female stays with the babies, caring for them and protecting them from predators. Part of her job is to keep track of which babies’ turn it is to eat next. The male hunts tirelessly to feed his family of five. The male and female do spend several hours each day huddled together sleeping and preening each other.

Camouflage
In addition to all the above adaptations it is important that owls be well camouflaged for where they sleep. Owls are predators, and prey animals such as squirrels and small birds do not like predators sleeping where they live. If they find an owl sleeping in or near where they live, they harass it during the daytime, when the owl is trying to sleep, until the owl leaves. If you watch the sky you will sometimes see a larger bird being chased and harassed by smaller birds, maybe that large bird is an owl.

Look online and see if any owls live in your area.

  1. What continents have owls native to them?
  2. What is the smallest species of owl?
  3. What is the largest species of owl?

1406266378Blair Lee M.S. is the the founder of Secular, Eclectic, Academic Homeschoolers. When she’s not busy doing these things, she’s busy writing or working on service projects. She is the author of the critically acclaimed Real Science Odyssey Biology 2 and Chemistry 1, http://www.pandiapress.com/publications/real-science-odyssey/. She is currently working on Astronomy and Earth Science 2 for the series.


(Answers: 1 – All continents except Antarctica, 2 – An elf owl, it weighs 31 grams and is 13.5 cm tall, 3 – Blakiston’s fish owl, it weighs 2.95 to 3.6 kg and is 60-75 cm tall