The Killing Fields

Meadow Voles skulls on Parade

The shrubby thickets of Lake Erie Metropark are host to an annual influx wintering Long-eared Owls. The birds gather together into daytime roosts numbering anywhere from 2 to 15 individuals. Every year is different – different roost locations, different number of owls, and different degrees of frustrations in trying to find them. I have frequently talked about these intense-looking owls and posted photos (in good years, anyway). The last few winters were not a good Long-eared Owl years. There were only a few about and they were exceedingly skittish. This past winter made up for all that. It was a good year with upwards of a dozen birds congregating into one roost.

You may ask why I am posting an entry about wintering owls at this stage. After all, it is Spring now and, even though there is a brand new cover of snow on the ground as I write this, we need to talk about baby animals, flowers, frogs, and the like. Our winter owls did finally flee the coop only a short time ago. They lingered well into April as if knowing that spring would be slow in coming, but the real reason was probably due to the good food. You see, this past winter was also a good year for mouse-like rodents. Or, perhaps I should re-phrase that and say that it was actually a bad year for mouse-like rodents because Long-eared Owls eat lots of mouse-like rodents.

The departure of the owls provided a golden opportunity to go through the pile of pellets left on the ground under the roost trees. You can imagine how many pellets would accumulate from 12 barfing birds over the course of a winter (“on the 12th day of Christmas my true love gave to me, 12 barfing birds, 11 hooters staring, etc, etc, …. 5 golden mice, 4 dropping turds, 3 mouse heads…). You could also imagine how much crap accumulates as well. Fortunately, the crap (euphemistically referred to as white-wash) washes away. The pellets, which are composed of undigested bone and hair, remain fairly intact.

The ground beneath the main Long-eared Owl roost – the killing field – was carpeted with winter meal remains. Many of the earlier pellets had disintegrated into a gray hair carpet finely peppered with bones. Hundreds of intact pellets lay on top of that layer. In all, about 290 whole specimens were collected. Long-eared Owl products are about 3 inches in length and about the diameter of small dog poo. Apart from a communal roost it would be hard to peg the owl species to the pellet, but in this location there can be little doubt regarding origin. There were no small dogs roosting in this grove of trees.

These pellets were carefully picked apart and the boney remains were extracted. Even though there were all manner of skeletal bones present in the hairy milieu, the skulls and lower jaws were the primary targets. It is difficult to define species level based on phalanges, ribs, and femurs. Skulls are much more diagnostic. The final tally was: 293 Meadow Voles, 11 Short-tailed Shrews, 9 White-footed Mice, and one lone bird (not a partridge in a pear tree, however – probably a White-throated Sparrow). In other words there was, on average, about one Meadow Vole per pellet (see below and detail here – note that the shrew skulls are on the top left row, the White footed Mice on the top row center, the bird skull on the top row right. All the rest are Meadow Voles)

What are we to draw from this little exercise? Well, for starters, there are no surprises here. Long-eared Owls are known to favor marshy lowlands adjacent to marshes for their hunting grounds. Such places are the favorite haunts of Meadow Voles – short-tailed, cigar-shaped mice that make runways through the grasses – and thus the joining of this flesh to these owl innards. Secondly, the Shrews and White-footed mice are signs of opportunistic feeding. If a shrew is bold enough to present itself on a moonless night then it will eaten. The bird remains are a bit more unusual, but they probably represent an early riser that got up a bit too early or a party bird that stayed up too late. Perhaps there is a lesson, or a fable, here for all little birds to heed.  At any rate, White-throated Sparrows spend a lot of time on the ground and often scramble about on the ground like mice. If any bird is asking for an owling, this one is it.

Finally, there is a single strong message evident from this study. If you are a Meadow Vole living at Lake Erie Metropark, there is a neon target on your back. It is no wonder that Meadow Voles are nervous and constantly upset.

Now that the Long-eared Owls have departed the roost and returned to their spring/summer breeding areas, our local voles now have one less predator to angst over.  The voles will spend the rest of the season making little mice which in turn will provide the hair, bones, and teeth for next year’s winter owl pellets.

Thinking about next year

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