April 2025 Natural Mystery Answered

We received a wide range of guesses for our April Natural Mystery, including snakes, turtles, and a diverse selection of semi-aquatic mammals. The tracks themselves are quite obscure, so folks needed to use track pattern, location, and context clues to interpret this challenging trail. Congratulations to Liz Snair and one anonymous tracker for sorting through the evidence and identifying who made these tracks.

This is the trail of a North American beaver (Castor canadensis).

I’m going to turn this over to our anonymous contributor to explain the evidence:

"These are beaver tracks. The proximity to the water and the central drag suggests to me an aquatic, tailed animal. In Minnesota, that could be muskrat, mink, beaver or river otter. The first two I ruled out because of the size of the prints, they each have relatively small paws, and the prints here look larger than 3". That puts them in the size class of beaver or otter. The only print that I kind of make out is the one that's up and to the left of the marker and the "tail" track. It looks like a back left foot with a small indentation in the front, which could be the front paw. The back foot I can see somewhat elongated toes (2 clearly with the side of the foot obscured) with an elongated foot pad. This seemed more reminiscent of beaver than otter, which have more toe bean forward type prints. The gait is also more indicative of beaver, as the prints are all relatively close together, which suggests the creature is moving slowly. The tail track sort of implies a waddle type movement as it's changing direction slightly with each step. This all says beaver to me."

That pretty much covers it! I’ll just add a few more notes about how we can rule out some other candidates.

Otters keep their bodies and tails lifted off the ground when walking and loping. When otters slide, the drag marks are straight, rather than sinuous. Otters commonly slide on snow and ice, and sometimes on mud, but rarely on dry sand.

Pond turtles, such as painted turtles, may drag their plastron when walking, but their tracks and trails are much smaller than we see here (as in this iNaturalist observation). Very large male snapping turtles may leave tracks 3.5” across and trails 15” wide, approaching what we see here. Snapping turtles drag their tail while holding their plastron off the ground as they walk, leaving a narrow central drag mark (as in this observatione), rather than the broad drag mark we wee here. Turtle trails also show proportionally sorter strides, with stride length roughly equal to trail width.

Snake trails would lack the footprints we see on either side of the drag mark. And even our largest native snakes, like this bullsnake, leave trails that are narrower and more sinuous than we see here.

Finally, I’d like to point out the asymmetry of the track pattern. Note how each left step appears relatively long and each right step relatively short. This is something I have noted a few times in beaver trails (and occasionally in other species as well). I began exploring this pattern in this iNaturalist observation I made in 2021.

Congratulations again to Liz and our anonymous tracker. And thanks again to everyone who sent in a response to this especially challenging Natural Mystery.

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