Owl Pellet Lab

On 2/23/2016, I conducted an owl pellet lab with a partner. The objective of this lab was to determine what animal the owl had eaten based on the bones from the owl pellet.

In this lab, my partner and I slowly dissected the owl pellet with a probe and forceps into two piles, one with only feathers and one with only bones.

Then, we used diagrams and pictures of the major bones of typical animals that an owl eats, such as a vole or a rat. After comparing the bones that we found and the pictures of the major bones of the different types of owl prey, we concluded that our owl ate a shrew. A determining factor in deciding that the prey was a shrew was the pelvis. The vole, shrew, and mole have very differently-shaped pelvises from each other, so it was easy to tell which pelvis we had. Since the pelvis we had was quite vertical and had two large holes on each of the pelvic girdles, we decided that our pelvis came from a shrew.

Furthermore, the back lower leg that we discovered had quite a distinctive look as well; the end of the fibula of a shrew is quite large compared to those of voles and moles, so we decided that the back leg also came from a shrew. Considering that we did not have that many bones in the first place, we concluded that all the bones came from one animal. Because we had two distinctive factors that pointed to a shrew, we decided that the owl ate a shrew. We could not use the dichotomous key because we did not find a skull in our owl pellet, but there ended up being other distinctive factors anyway.

Compared to the skeleton of a human, the shrew has similarities and differences to the human skeleton. For differences, first off, the human pelvis is more horizontal than the shrew pelvis which is more vertical. This is a result of the way we walk; humans walk upright on two legs and shrews walk with four legs on the ground, so our pelvises will obviously be shaped differently. Second, shrews have very sharp teeth at the front of their mouths/skulls, so as to bite, and all of their teeth are quite spiky. On the other hand, the human skull is rather round, kind of like a circle, and we also have canines at the front and molars at the back of our mouths.

 Lastly, the scapula of a shrew has two protruding bones from the main shoulder blade. On the other hand, the human scapula is just one flat bone, with no protruding fragments.
For the similarities between the shrew and human skeleton, our back and lower leg bones (tibia and fibula) look quite similar, as they are fused at one end. Furthermore, the tibia is also a bit thinner than the fibula, as it also is on the human skeleton. Second, the shrew pelvis also has two large and noticeable pelvic girdles that look similar to those on a human skeleton; the pelvises of the vole and mole do not have as noticeable pelvic girdles. Lastly, my partner and I discovered many small bones that look very similar to each other, and concluded that they all formed the vertebral column. After looking at a diagram of the vertebral column of the human skeleton, I noticed that the individual vertebrae look almost exactly the same as the vertebrae of the shrew spine.