[at-l] B-Owl Movement. Re: Feeling Like Spring

RockDancer rockdancer97 at comcast.net
Mon Mar 7 09:48:05 CST 2011


Hi all,

I’ve had a great time in past 2 weeks reconstructing the contents of owl pellets that I collected in the local state forest.  There is probably more I could learn but without any training I could sort the mess-o-bones out this way.

 

Site 1 – Northern Saw-whet Owl eating White-footed Mice

Early on I thought this site had either a Northern Saw-whet Owl or an Eastern Screech Owl. This is based on pellet size and the dense white pines where they were found. The 5 pellets contained 5 animals but only 4 skulls. From the dental records and skull size they are all genus Peromyscus mice. In my area we have only the White-footed mouse and the American Deer mouse. From the size of the pellet the bird is narrowed down to only the Northern Saw-whet Owl. Now I’d like to see it.

 

Saw whet owls will kill as many as 6 mice in succession and them in Winter pantries. Later they will brood on the mouse-icle to thaw for eating. If food is plentiful they will eat only the heads. Deer mice is the primary prey and the pellet length is .75 inches.

 

Screech owls produce 2-4 pellets each day and pellet length is 1.5 inches long. In the winter they will hunt open ice holes left by fishers. We have fishers and river otters in the woods at this location.

 

Site 2 - Great-horned Owl eating Meadow Voles and a Grey Squirrel

I saw the bird and the pellets are from the base of the nest tree, the nest about 90 feet up in a conifer. The 2 pellets I collected were a surprise because they contained partial skeletons, and the skeletons were perfectly complementary. This means the bird emptied it’s stomach in 2 “surges” and all the bones were in the stomach at the same time. Taken together I had 5 skulls, 10 pair of lower jaws, 10 pair of leg bones meeting in ball-socket joints (like our hip-femur). All 5 animals are Meadow Voles. We have 3 voles in this area but the skull size determines them to be Meadow Voles.

 

But the pellets also contained a mystery. An intact chest bone, a larger ball-socket joint (5x larger than a vole), 5 odd shaped vertebrae too large for vole and many flat flexible fragments of what I assume is the skull cap. So this owl also ate something much larger than a vole (which in this case is larger than the mice). Candidates are Flying Squirrel, Red Squirrel, Grey Squirrel, rabbits, skunk, opossum, etc. Based on population I’ll be content to call it a Grey Squirrel. It’s body is 2.5x the length of a Meadow Vole, not quite the 5x increase in size indicated. But then I don’t know how these things scale up. Perhaps the hip joint scales at 2x the rate for the length of body? 

 

That’s all I’ve got for this project. After cleaning and sorting the bones I used the kitchen microwave to sterilize all I had, tossed the rest. This allowed me to handle the bones without worries. Turns out you can get some enteric bacteria from doing this so be careful out there!

 

RockDancer

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