Pellet Schedules

Ready for a rousing game of “Who Cast that Pellet?”  Take a guess with this first pellet:

Pellet #1:

Theo pelletSee the bone fragments poking through this pellet? Theo the Great Horned Owl left this after eating a furry white rat. His stomach muscles and juices broke down the meat, allowing the meal to continue into the intestines. But indigestible fur and bones remained in the stomach where they were pressed together and, eventually, coughed back up. The time required for this process depends on the size of the meal: larger meals take a longer time to process.

Pellet #2:

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This pellet has smoother edges and no visible bones. If I split this pellet open, we would only find fur. Carson the Red-tailed Hawk ate the same meal as Theo, but hawk stomach acid is much more acidic and can disintegrate bone. The bones of her rat passed through, but the tough fur was still cast back up as a pellet.

While owl pellet schedules depend on when and how much they eat, hawks adhere to a circadian rhythm. In one study, Red-tailed Hawks cast a pellet at the first light of the day regardless of when they were fed the day before. They are even known to cast a pellet after a fast day with no food in their system. Their routine pellet casting at dawn may reflect their hunting strategy. Hawks require daylight to hunt, so emptying their stomach in the morning will prepare them for a fresh meal. Owls, on the other hand, can hunt during day or night, so their system simply empties after the food has been digested.

Learn more about raptor pellets in this Raptor Physiology chapter.

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Nighttime Displays

generic GHOW.jpgDuring daylight, a Great Horned Owl’s most prominent colors are its mottled brown and black hues. This camouflaging pattern keeps the owl hidden so it can get a good day’s rest. Without it, the owl might be spotted by angry crows or blue jays and get chased away from its roost.

As the sun goes down and the owl wakes up, the forest – and the owl itself – is draped in a new light. The owl’s dark colors and fine patterning nearly disappear in low light conditions. Instead, it is the white throat patch that stands out. For nocturnal animals, contrasting blacks and whites are the most visible and can serve as a warning coloration, just like poisonous monarch butterflies are brightly colored in daytime. Picture a skunk’s bold black and white stripes that act like a spotlight in darkness, highlighting an animal that you would do well to stay away from.

I have yet to find an official explanation for the Great Horned Owl’s relatively bright throat patch, but I have my own theory. When resting, the patch appears as a thin line, perhaps minimizing the bright color to help camouflage while hunting. But when the owl needs to defend its territory, the throat inflates as he calls out a low “whoo-whoo whooo whoo whoo,” and the white patch expands to make a visible display in addition to the audible proclamation.

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Theo rested in the classroom overnight this week to escape the cold temperatures. You can most clearly see his white throat patch in the photo (and the white rope covering his perch).

Chilly Mornings

The first thing I do every morning is check on the birds to make sure everyone is okay. There’s always a little voice inside my head that echos “what if?” and I subconsciously worry that something terrible might have happened overnight. Luckily, I always find three healthy birds staring back at me.

Peeking in at the birds eases my mom-like concerns and also gives us the chance to say “good morning” to each other in our own way. Theo’s mew often has evidence of his busy night and, as the sun comes up, the owl tries to get some shut-eye. When I look in, he responds with a hiss as if telling me he wouldn’t like to be disturbed.

 

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I make my way to the next mew to check on Carson the hawk, who on this morning was basking in the sunshine at her window. The air felt colder than my car thermometer indicated and Carson seemed to agree. She sat with her feathers all fluffed to increase the effects of her down insulation. One foot was balled up, relaxed. Soon that foot tucked up and disappeared into the cloud of feathers to keep it nice and warm. Her eyes followed me as I continued on to the last resident.

Aldo the kestrel is always the most alert and active at sunrise – a real “morning bird.” I peek into his mew and he flies straight toward me, landing on the perch in front of the window. He trills and I imagine he is saying “good morning!” right back to me.

 

Spring Cleaning

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In spring, I love to find wildflowers blooming, to wait for migrating birds to return, and (perhaps most of all) to connect the outdoor hose. Winter makes a frozen mess in the raptor mews that we try to clean with buckets of hot water, but we can’t get everything. The birds don’t seem to mind since they spend their time on perches, elevated above the muck. But it was clear to us they required a heavy spring cleaning. We spent a full morning this week rinsing, washing, scrubbing, raking, and disinfecting every surface of the mews. With the help of above-freezing temperatures and a little elbow grease, the mews are practically sparkling!

Weights

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Animals are amazing actors with the ability to mask injuries and illness. They want to hide any weakness from potential predators or competitors, while still finding their basic needs to survive. Raptors will keep hunting for food even with extreme injuries. When our Great Horned Owl, Theo, was rescued, he appeared to be well fed. The rehabilitators believed he was actually running down mice despite having a broken wing. Since their behaviors rarely show signs of illness, their weight is often the first sign of a problem. We take daily or weekly weights to track our birds’ health. The key is knowing what is normal for each bird.

I chart each bird’s weight to keep an eye on patterns. Aldo’s chart, for example, shows daily fluctuations and seasonal changes. His weight last summer hovered around 108 grams (3.8 oz) and increased in November. The higher weight gives him a little extra buffer against cold temperatures through the winter. As spring approaches, he has begun shedding weight in preparation for breeding season and warmer weather. With a baseline of these normal weight patterns, I can identify abnormalities and keep him at healthy weight.

Who’s awake?

Deep in the middle of winter, Great Horned Owls are already planning for chicks. Pairs begin singing duets in November to strengthen their bond before the first eggs are laid in late January or February. It is difficult to distinguish males and females in daylight since they have the same plumage (and females are slightly larger), but their calls provide hints once the sun goes down. The owls take turns calling into the night, repeating a phrase that sounds like “Who’s awake? Me too.” These calls are usually very distinct; males have a low-pitched voice compared to the female.

We are fairly sure that our Great Horned Owl, Theo, is a male based on his body weight, but the true test will be comparing his voice to another owl. Jayme, Living Collections Assistant, heard two Great Horned Owls, probably Theo and a wild bird, conversing in Cable earlier this week. We’ll have to listen again to find out if he is courting a high-pitched female or defending his territory against another deep-voiced male.

 

Cold Snap

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We eased into December with some mild winter weather, but this week gave us a good reminder of our northern latitude. Red-tailed hawks and great horned owls are common winter residents in Wisconsin. Owls are perhaps the best suited for winter with masses of fluffy down and extra feathers covering their toes. The wild barred owls that I hear calling in my backyard can cope with these temperatures, but our birds’ ability to stay warm is compromised by their permanent injuries.

Both Carson (red-tailed hawk) and Theo (great horned owl) had broken wings that never healed properly. It not only affects their ability to spread the wing for flight, it also means they cannot fold the wing completely. When standing on a perch, they can’t fold the wing against their body as usual, leaving an open door for the cold air. It might be the equivalent of you putting only one arm through your winter jacket and stepping outside. Since they can’t keep one side as warm, we give our birds the luxury of indoor heating when the outdoor temperatures dip below -10oF.