CSI Rockford, watch out! The naturalists at Severson Dells will give you a run for your money!
Last Friday, August 31, one of the Forest Preserve staff brought us an owl pellet that he found up by the farm. It was quite large, with long fur attached on one side, and a very clean jaw bone sticking out.
Now, I love dissecting owl pellets – they are like little furry Christmas presents, full of goodies and you never know just what you might find. I’ve dissected probably hundreds of pellets over the years, mostly with students, but a few on my own. The majority of the time one finds rodent bones in them, which is no surprise - mice and voles make up a huge part of an owl's diet. A handful of times I’ve found shrew bones (red and black teeth always give them away). I’ve found bird skulls maybe three or four times. Jerusalem cricket mandibles were probably the most exciting thing I found…until this last week.
As soon as I saw that pristine jawbone sticking out the side, I knew we had something special – that was no rodent jawbone. The molars were long and pointy, and the teeth went all the way from the back to the front of the jaw (rodents have a space between their molars and incisors). But it had to be a "small mammal" – the bone is less than an inch in length.
I decided to do a Facebook Live video while dissecting it – a new challenge for me. Got my phone set up, balanced on bundled knotweed stalks in lieu of a tripod, and off I went. Each piece I pulled out was exhibited and pondered over. Some bones were obvious: femur, shoulder blade, ribs, vertebrae. There was the pelvis with a femur still attached. There were two jaw bones (sadly, no skull).
And then I found a foot.
Now, this wasn’t just any old foot. Most small mammals’ feet are composed of numerous tiny, fragile bones. If you are lucky, you find them still articulated. This foot, however, was huge. In truth, it was the claws I found first – enormous claws attached to a large, wide foot with sturdy, broad bones. I was left with no doubt as to what I had: a mole.
I quickly looked up online to see what species of moles are found in our region, and was disappointed to find only one: the eastern mole (Scalopus aquaticus), also called the prairie mole. Still, it made the choice pretty easy.
Two mysteries still remained, however.
One: what in the world were these two very thick bones that I found? At first I speculated they might be part of the skull, based on what I could see in the morphology of the first one I found; once the second one, identical in every way, showed up, this theory was out the window. There was no way these were part of the skull – they were definitely two separate bones.
Today’s search online for a mole skeleton provided the answer: the humerus! The mole’s skeleton is quite unlike those of other small mammals when it comes to the front legs, and considering that this animal is using powerful front legs to move mountains of earth every day, that shouldn’t come as a surprise. The thickness of these bones attests to the strength they must have to support the mole’s fossorial lifestyle. The shape of the bones, however, still leaves me saying “huh!” – the humerus for most mammals is long and thin – think your upper arm. What an amazing adaptation!
The second conundrum was two-fold. I found a molar that just did not come from this animal – way too big, and structurally different. Add to this the fur that made up the pellet: there was not only the dense dark fur of the mole, but also some long pale fur that in no way ever came from a mole. This fur was too long for any other small mammal (plus the tooth was too big). I thought at first rabbit, but, again, the tooth morphology was all wrong. This morning the three of us in the office sat down to wrack our brains to come up with an answer as to what else this owl had eaten.
“What about opossum,” Greg said.
OF COURSE! The answer was so obvious! That fur could be nothing BUT opossum. I quickly looked up the dentition and am fairly confident that the molar is a ‘possum molar. But why there is just the one bone/tooth from the ‘possum will remain a mystery.
Here is what I surmise happened: the owl caught a mole and had a lovely meal of it, and then later washed it down with an opossum chaser. While eating the ‘possum it ingested some of the fur, no doubt while plucking the flesh for swallowing. There was no reason to ingest the bones – meat of the animal was likely plentiful and easy to get at.
What a wonderful find this owl pellet was - thank you, Mike!!!
May YOUR days be filled with such treasures as this.