With an ice storm the night before and daytime highs in the low 20’s, few people are thinking about hiking through the forest in search of owls. Ornithologist John O’Donnell, from the Friends of Cedarburg Bog, led our group of 18 MUHS students and adults through the UWM Field Station land at Cedarburg Bog in search of some of the most interesting birds in WI, owls.

Ice covered trees

Ice covered trees

The night before our walk, several inches of snow and ice covered much of WI. These sorts of storms can really disrupt feeding habits of owls causing them to increase their hunting efforts in future days to prevent starvation.

We began our night at the UWM Field Station learning about the Cedarburg Bog and the ecology of Owls. The Cedarburg Bog was Wisconsin’s first State Natural Area, which is a special protection designation for ecosystems exemplifying pre-settlement features. The bog covers 2000 acres and is home to many unique plants and animals including carnivorous pitcher plants. See last year’s blog post from our hike through the bog: Cedarburg Bog State Natural Area

Learning about Cedarburg Bog Ecology and Owl Adaptations

Let me first describe some of the amazing adaptations these nocturnal specialists have. Of our 10 species of owls that call WI home, only 6 are residents year round. Of those 6 species, really only 3 species are regularly seen or heard by outdoor enthusiasts or even birders: Great Horned Owl, Barred Owl, and Eastern Screech Owl. These were the 3 focus species of our Owl Prowl.

Adaptations- Hearing: Owls have an amazing sense of hearing. This is no accident. Many owl species that spend the winter here depend more on hearing than sight to find their prey scurrying under the snow. Owls have a facial disk that acts like a satellite dish funneling sound to their ears. The ear tufts on a Great Horned Owl are not its ears but merely feathers. The sound funneled from the facial disk ends up in the ear openings of the owl which are assymetrical on each side of the skull. This sound hitting the ear openings at slightly different times is enough to help the owl pinpoint their prey with extreme accuracy. For example, Great Grey Owls (our largest owl) can hear its prey under 3 feet of snow! Even at 30 yards away, an owl is able to pinpoint its prey within 2 centimeters by hearing alone.

Adaptations-Eyesight: Hunting at night presents some big challenges because of the low light conditions. Owls have tackled this problem through some amazing eye adaptations. To start, owl eyes are huge in proportion to their skull size (like humans having grapefruits for eyes). This large size is what can allow a tremendous amount of light into the eye and to the retina. Owl eyes actually weigh more than their brain and take up the entire eye socket, not leaving room for muscles. This means the owl cannot move its eyes side to side but must be able to turn its neck back and forth to see other directions. Inside the retina are millions of times the number of “rods” that human eyes contain. These rods are what allow us to see in low light and only register in black and white. Owls also have a highly reflective layer in the back of their eyes (tapetum lucidum) which bounces the light around to make efficient use of it. This is the same structure that makes dog and deer eyes glow at night when shined with a flashlight. Lastly, some owls are thought to see in infrared wavelengths and thus be able to perceive heat emitted from their prey.

Adaptations-Silent Flight: It is astounding when owls can fly up into a tree right next to you without you hearing them. This is exactly what happened to us on the Owl Prowl when a Barred Owl landed 15 yards away in a tree. Lucky for us, the tree was covered in ice and when the owl landed, some ice was knocked off the tree, notifying us of the owl’s presence. Owl wings are specially adapted to be silent. This is necessary because the ambient noise at night is very low and any noise an owl would make descending on its prey would be enough to make the hunt unsuccessful. Their feathers have hooked barbs to stitch the feathers together eliminating sound passing through. They also have a serrated leading primary feather to disrupt sound passing by. Lastly, even their feet are covered by feathers. Unlike hawks, this allows owls to glide throughout the forest without detection. Feathers on the feet are also important insulation for birds like Snowy owls that inhabit extremely cold areas.

The 3 target species of our Owl Prowl were Great Horned, Barred, and Eastern Screech Owls. Great Horned Owls are actually sitting on their eggs right now (the earliest nesting bird in North America). This early nesting is timed so that when the fledglings are at their most demanding for calories, the rodent populations will be booming i.e. rabbits and voles. The method we attracted owls to us was through the use of audio recordings broadcasted on a speaker. These acted as territorial challenges bringing the owls in. We were able to hear a Great Horned Owl calling (likely from its nest) and were entertained by a male and female Barred Owl curious about these foreigners in the forest. We later tried for Screech Owls at Riveredge Nature Center to no avail, reminding us that these are elusive and secretive creatures.