The easiest way to learn what owls have for dinner is to figure out where they roost. Old barns and churches are particularly good places to look. On the ground below the nest you are likely to find a scattering of gray-brown pellets about the size of the last two segments of your thumb. Each one contains the left-overs from the owl’s previous meal. (If you are not the outdoorsy type, you can order owl pellets at Amazon.)
Compared to most carnivorous birds, an owl does not use its beak and talons to tear its prey into bite-size pieces. Rather, an owl swallows its prey whole. Then in its digestive tract’s uppermost chamber, high concentrations of acid and enzymes break down the muscle and fat into a digestible liquid. Bones and fur resist this process, so hours later the owl regurgitates the leftovers as a compressed pellet. Then it is ready for the next night’s hunt.
Some other birds also form and dispense pellets, but their nesting spots may be less obvious than an owl’s; and since their pellets may be much smaller, they are hard to find.
Gently teasing apart this compressed lump of undigestables will reveal the jumbled bones of three to four small rodents. Their jawbones are easy to recognize; and with a pictorial guide, which is readily available on the internet, the specific type of prey can be identified.
By dissecting owl pellets, grade school students can get a lesson in osteology. Ecologists can ascertain seasonal variations in owl diets, which may also include bats and small birds. It is the molecular biologists, however, who are currently having a field day. For one thing, owls can collect study specimens without causing any collateral kill that human trapping might entail; and owls hunt with impunity even in protected areas. The biologists extract the DNA from the mandibles of these small, man-avoiding, hard to trap, pelletized animals and use it to study population genetics, both across species and over time. Owls and regurgitated bones are thereby helping answer questions about habitat maintenance, climate change, and genetic diversity. Whoo knew?
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