A January Owl Ecology Class

I am late with this post. My apologies to the young ornithologists at the Nazareth Intermediate School in Nazareth, PA. In January I had my annual visit to this school where I did a lesson on Owl Ecology. We talked about the 4 common owls of the Nazareth, PA area, the Eastern Screech-owl (Otus asio), the Great Horned Owl (Bubo virginianus), the Barred Owl (Strix varia) and the Barn Owl (Tyto alba). Our discussion covered the identification, behavior, and habitat needs of these owls. We also talked about how students might do field studies of the owls with the help of their parents or other responsible adults.

We then dissected owl pellets to see what food preferences the Barn Owl has. The pellets we dissected were from western Barn Owls purchased from Pellets,Inc. (see link below to the right). Here is the data we collected.

Thomas/Miller classes 24 pellets, 54 mice, 6 shrews, 2 moles, 1 bird

Kimble/Velekei classes 26 pellets, 52 mice, 4 shrews, 4 moles, 0 birds

Roth/Giemza classes 24 pellets, 57 mice, 6 shrews, 1 moles, 1 bird

Emrick/DeBoer classes 24 pellets, 37 mice, 8 shrews, 5 moles, 1 bird, 1 insect

Genua class 12 pellets, 28 mice, 6 shrews, 3 moles, 1 bird

Reed class 10 pellets, 12 mice, 5 shrews, 1 moles, 0 birds

Rohn/Quinones classes 23 pellets, 45 mice, 4 shrews, 1 mole, 0 birds

Reynolds/McCarron classes 25 pellets, 50 mice, 6 shrews, 3 moles, 2 birds

Analysis

One hundred sixty-eight pellets were dissected by fourteen classes of 4^th graders. A total of 335 mice, 45 shrews, 20 moles and 6 birds were found. In addition to these prey, one pellet included the remains of an insect. These remains appeared to be leg segments from a something like a mole cricket (Gryllotalpidae family). Taken in whole this data indicates that on average Barn Owls eat 2.42 animals per meal (the pellet is a result of a meal – in one night the owls might produce 3 or 4 pellets as they feed, then stop to rest and digest and then go back to feeding throughout the night). This average matches findings with other owl pellet dissections conducted with other schools (see archives for other owl pellet dissection results).

In our discussion before the dissection we had hypothesized that mice would be the favorite food, with shrews second favorite and moles and birds tied for third. It is clear that mice indeed are the most common prey and that shrews are second. It seems though that moles are more often eaten than birds by a factor of three. Look through other owl pellet dissections in the archives of this blog and see if this bears out with the findings in those sessions.

I wonder if the owl ate the insect as a primary prey or if it might have ingested the insect when it ate a mole that had eaten the cricket. Moles feed on underground insects and other invertebrates. It is possible the mole had just eaten the cricket and then was eaten by the owl. Unfortunately I did not take notes as to what else was found in the pellet with the insect parts. If mole remains were found along with the cricket remains that would support the idea that the owl ate a mole that had eaten the cricket. If I ever find insects parts in owl pellets in the future I know that I will be sure to make note of what other prey were found in the same pellet.

The owl food chain affects farmers. Since mice, and these mice are for the most part are field mice (Microtus spp), are the favored prey the owls, eating them affects farm production by reducing the amount of plant crops eaten by the mice. I have a little math exercise I call “Mouse Mathematics” that I will post in the near future that illustrates what this cost savings for a farmer might be. Look for it being posted soon.