My apologies to the 4th grade Ornithologists at Bushkill Elementary School in Nazareth, PA. I had meant to get their data online sooner but got tied up in a conference on children’s summer camps and nature programs.
During the week of January 26th we investigated the predator preferences of barn owls by dissecting owl pellets. The owl pellets were purchased from Pellets Inc. and come from the Pacific Northwest. Here is the data we collected regarding the kinds of prey barn owls eat and how many they eat in a meal that produces a pellet.
DeBoer’s class - 10 pellets dissected produced 23 mice, 1 shrew, 1 mole, 1 bird
Roth’s class - 11 pellets dissected produced 24 mice, 0 shrews, 0 moles, 0 birds
Hahn’s class - 10 pellets dissected produced 23 mice, 1 shrew, 0 moles, 0 birds
Apruzzi’s and Stump’s classes (combined) - 22 pellets dissected produced 41 mice, 1 shrew, 2 moles, 0 birds
In each class we had discussed our hypothesis that mice were the most preferred food, followed distantly by shrews, with moles and birds tied for the least desired. With each class it was clear that barn owls definitely prey more on mice than any other animal. In each class though, it wasn’t as clear as to any difference in preference for shrews, moles or birds. The percentage of prey eaten listed by class follows:
DeBoer – 88% mice, 4% shrews, 4% moles, 4% birds
Roth – 100% mice, 0% shrews, 0% moles, 0% birds
Hahn – 96% mice, 4% shrews, 0% moles, 0% birds
Apruzzi and Stump – 93% mice, 2% shrews, 5% moles, 0% birds
We agreed that we did not have a large enough sample to have a clear picture of the predation on the three less favored kinds of prey. In order to collect more data we would need to dissect more pellets. Much as the students would have loved to done this neither time nor funding allowed it. By combining the information for all three groups though, a different picture emerges. Taken in whole the 4th grades dissected a total of 53 pellets and found the following: 94% mice, 2.5% shrews, 2.5% moles, 1% birds. Perhaps we still do not have a big enough picture and should take apart even more pellets. Since we can't take apart more pellets we can look at data collected by other schools that I have worked with - see Previous Posts: Owl Pellets and Predator Prey Relationships for Monday, January 19 and the data collected by Jefferson Elementary students. How does this alter our conclusions about barn owl food preference?
One final aspect of predator prey relationship is illustrated with our dissection, the balance of nature, the number of predators balance with the number of prey. Our dissection revealed that 118 animals were eaten to produce 53 pellets. That is an average of 2.2 animals per pellet. An owl will produce about 4 pellets a night. That means in one night a barn owl will eat about 9 animals (mostly mice). In one year that owl will eat about 3,300 mice (and other small animals). Mice are prolific breeders. Owls keep the mouse population in balance by preying on these many small creatures.
Students are busy dissecting owl pellets looking for the bones of the owl's prey. The owl eat the prey whole. Very quickly in the digestion process the bones, fur and feather (in the event that the owl has eaten a bird) are packed into a ball and regurgitated.
Here is some of the hands-on investigation that reveals what the owl ate to produce a pellet.
