Here is an analysis of the results of the owl pellet dissections done by the 4th grade scientists at Nazareth Area Intermediate School back in January. I am sorry for the delay in getting this on my blog. I hope the NAIS students aren't too disappointed that it has taken this long to post the results here.
Dissection Results
In Malachowski’s Home Room class we found 37 mice, 3 shrews, 0 moles, and 1 bird in 13 pellets.
In Kimble’s Home Room class we found 28 mice, 3 shrews, 0 moles, and 0 birds in 10 pellets.
In Kimble’s Science class we found 37 mice, 0 shrews, 0 moles, and 1 bird in 13 pellets.
In Wasser’s Science class we found 31 mice, 2 shrews, 0 moles, and 0 birds in 11 pellets.
In Malachowski’s Science class we found 37 mice, 5 shrews, 0 moles, and 0 birds in 13 pellets.
In Giemza’s Science class we found 29 mice, 4 shrews, 0 moles, and 0 birds in 12 pellets.
In Genua’s Science class we found 31 mice, 2 shrews, 1 mole, and 1 bird in 13 pellets.
In Genua’s Home Room class we found 30 mice, 1 shrew, 0 moles, and 0 birds in 11 pellets.
In Giemza’s Home Room class we found 28 mice, 5 shrews, 0 moles, and 0 birds in 12 pellets.
In Wasser’s Home Room class we found 20 mice, 2 shrews, 0 moles, and 0 birds in 12 pellets.
In Thomas’s Home Room class we found 33 mice, 2 shrews, 0 moles, and 0 birds in 12 pellets.
In Roth’s Home Room class we found 27 mice, 1 shrew, 0 moles, and 1 bird in 12 pellets.
In Thomas’s Science class we found 24 mice, 2 shrews, 0 moles, and 1 bird in 11 pellets.
In Roth’s Science class we found 23 mice, 4 shrews, 0 moles, and 0 birds in 12 pellets.
Analysis
In all we took apart 167 pellets and found 415 mice, 36 shrews, 1 mole and 5 birds. Clearly my hypothesis that mice or rodents are the most favored food is confirmed. The same could be safely said about shrews being the second favorite food. What about my hypothesis that moles and birds are tied for third place?
With 5 birds eaten compared to only 1 mole perhaps I need to rethink my hypothesis. Before doing this though, it might be good to look at our results in another way. What if we figured out the percent of the total for each kind of prey eaten? To do this we need find the total number of animals eaten by the owls found in the pellets we dissected. That would be 457 animals. To find the percentage for each type of prey we need to divide the number of that prey by 457, the total number of animals eaten. For mice that would be 415 divided by 457 for 91%. For shrews we must divide 36 by 457 with a result of 8%. The 5 birds eaten divided by 457 gives us 1%. The sole mole divided by 457 gives us a less than a half of 1% result.
Looking at the percentage of birds compared to moles eaten does give a slight advantage to birds but it is very close. It may still be argued that birds and moles are tied as a less favored food. If we take apart even more pellets we might find numbers of moles and birds that close this small gap. You can do this by comparing the findings that I have gotten with other classes at other schools that I've posted here on this blog.
I looked up what we found last year with the fourth grade ornithologists at NAIS (blog entry March 2011). Here is what they found: 168 pellets dissected resulted in finding 335 mice, 45 shrews, 20 moles and 6 birds. Calculating the percentages for these findings we get: mice 83%, shrews 11%, moles 5%, and birds 1%. There is a reversal of food preference between moles and birds. Why? Perhaps it might be a result of a difference in the numbers of birds and moles available due to changes in mole and bird populations from year to year; there might have been more moles or fewer birds around in 2011. Perhaps there were weather conditions that made it easier or harder to find a particular prey. For example a large amount of snow cover would make it harder for the owls to find moles since the moles live underground and would be covered by snow. Can we compare snow cover in the areas of northern California, Oregon and southern Washington (this is where the owl pellets come from) between the winter of 2010-11 and this winter?
How about if we combine the findings of both years? Here is what we get: 863 animals eaten divided up as follows: 750 mice, 81 shrews, 21 moles and 11 birds. In terms of percentages we get: mice 87%, shrews 9%, moles 2% and birds 1% (these percentages, as with the other percentages calculated here, are rounded off to the nearest whole percent). With the combined data we see that the percentage of moles and birds eaten is very close, and are basically tied for a distant third place as far being a favored food for the Barn Owls of the Pacific Northwest.
Take apart more owl pellets (a link to Pellets, Inc can be found to the right) and send your data to me. I’ll post it on my blog and we can see if that data supports my hypothesis or tells us that we need to rethink it. Have fun doing that and studying owls and their food chain.
