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| Boreal Owl Pellet Wasatch County, Utah |
(View on a large screen and click each image for a higher resolution view)
Why Pellets?
Well, here's a close up of the Boreal Owl pellet I retrieved after one of the owls in my last post hacked it up, briefly clutched, and then dropped it to the ground. This one-inch (2.54 cm) pellet came from an owl that is between nine and ten inches tall (22-26 cm), depending on whether it was a male (smaller) or a female (larger).
You may already understand the process, but I want to share with those who may not know how a pellet is formed and why it is expelled. Owls, and many other birds, have two stomachs or chambers that aid in the process of digestion. They swallow prey whole or in chunks, but they cannot digest the fur, feathers, teeth, nails, or bones of the prey. The first chamber essentially liquifies the digestible parts with enzymes and sends the partially digested meal to the second stomach, or gizzard, which breaks down the hard pieces, sends the digestible contents to the intestines, and compresses all the useless stuff into an oval shaped pellet. The owl has to regurgitate the pellet from the gizzard before the next meal so this process of creating and casting pellets typically cycles once each day. Many owls cast their pellets from their daytime roosts so locating pellets below trees, particularly conifers, or cliffs and manmade structures such as barns and silos is one way to discover their roosts.
When I realized that one of the Boreal Owls I was observing October 3rd was about to hack up a pellet I began capturing a series of images as quickly as I could. The image below shows the owl manipulating the pellet before dropping it to the ground.
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| This Boreal Owl expelled the pellet, grasped it, and held it next to its bill before dropping it to the ground. Uinta Mountains, Wasatch County, Utah |
Finding this species of owl, considered rare in Utah, was special. Watching one actually cast a pellet was extra special so I considered the pellet a parting gift to memorialize our time together. Drying it out and inspecting its contents struck me as a great way to learn more about the the diet of the owl. Boreal Owls are perch hunters so they wait for prey to appear and then swoop or drop down to take prey with their talons. Small mammals such as voles, mice, and shrews along with small birds and some insects make up the bulk of their diet.
Let the Inspection Begin
The pellet was set aside for a few days before I got around to unveiling the contents and capturing images with a macro lens. Mounting the camera on a tripod would have yielded crisper images, but handholding seemed to meet the need well enough when I added a flash and diffuser to the mix. I probably should have used a solution to remove all the fur from the bones, but I didn't. I kind of sound lazy with those explanations, but I was just really curious about the contents and my casual approach satisfied that curiosity well enough.
Pellet Quiz Time
The anatomical parts seem to belong to at least two mammals (voles?), because I can see jaws and hard pallets for two mouths. What rodent do you think is represented in the images? I forgot to use a ruler in this image to show scale, but all of it fit into that one-inch pellet shown at the top of this post. The jaw bones were probably 3/4 inches (1.9 cm) long. What parts can you identify before looking at the illustration I've created in the very last image? Please tell me in the comments if you see more identifiable parts and I'll try to add them to my labeled illustration.
Click on each image for a higher resolution view.
Drum roll! And the answer is (with a little help from my veterinarian friend):
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