January 2022 Natural Mystery Answered

Our January Natural Mystery proved tricky. We only got a few responses, and while everyone who wrote in identified the family correctly, no one agreed with my identification of the species. But then, these are uncommon tracks. This is not only the first time I have identified the tracks of this species at Cedar Creek, it may be the first time this species has ever been confirmed on the property.

These are the tracks of a Northern Flying Squirrel, Glaucomys sabrinus.

Flying squirrels are often illusive, even where they are common. With its abundance of snags, Cedar Creek offers good habitat for these nocturnal, cavity-dwelling sciurids. Though rarely seen, they are likely the second most common squirrel at Cedar Creek after Eastern Grays. We have found Southern Flying Squirrel tracks on several past Cedar Creek Wildlife Surveys. Prior to this observation, Northern Flying Squirrels had been suspected but not confirmed at Cedar Creek.

So how can we know these are the tracks of a Northern Flying Squirrel? We can begin with size.

The snow conditions make it a bit tricky to get precise measurements--especially for the length of the front tracks. It's always best to measure several tracks when possible. In this photo, we have two front tracks and two hind tracks, allowing at least some averaging. Taking my best crack, I put the front tracks at 1 1/16" long by 3/4" wide, and the hind tracks at 13/16" long (1 1/4" with the heel) by 3/4" wide.

Consulting Elbroch, Moskowitz and Animal Tracks of the Midwest 2ed, these track measurements narrow our list of sciurid suspects down to Red Squirrel and Northern Flying Squirrel. The trail width, however, measures just 2 5/8", which is outside of the published ranges for Red Squirrel bounding trails (though it is just barely outside of the range Moskowitz offers for Douglass Squirrels).

In addition to the trail width, the track pattern has a "boxy" appearance characteristic of flying squirrels. There are several features of flying squirrel trails that contribute to an overall "boxy" shape. Flying squirrels often register their hind feet nearly parallel, rather than tuned out as is typical for red squirrels and chipmunks. Flying squirrels often set their front feet more widely apart when bounding. And flying squirrels tend not to splay toe 5 on their hind feet very much, giving the outer edge of the hind tracks a straighter profile. Not all of these characteristics show up in every flying squirrel trial, but there are often enough of these features present to give an overall "boxy" look to the track pattern. In this case, we see the hind feet pointing nearly straight forward and toe 5 on each hind foot spaying very little.

Next lets look at morphology. Red squirrels leave long, slender toes impressions that often connect to the palm in the track. Flying squirrels tend to show slightly bulbous digital pad impressions that register separately from the palm. The negative space between the toe and palm pads is pronounced in both hind tracks. Given the depth these tracks are registering in the snow, we could expect a red squirrel to register the shafts of its toes.

Another feature we can look at is the relative position of toes 1 & 5 on the hind foot. In Red Squirrels, toe 1 is set just a little farther back than toe 5. In flying squirrels, toe 1 is set much farther back than toe 5. The positions of these two toes are clearest in the lower (left side) hind track. Here we can see toe 1 set considerably farther back on the foot than toe 5.

This was definitely a tricky ID. If you want to explore this observation in more depth, check it out here on iNaturalist, where you can view additional photos of the trail and offer your own thoughts and input.

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