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August 2020 Natural Mystery Answered

posted Sep 7, 2020, 12:04 PM by Jonathan Poppele   [ updated Sep 14, 2020, 8:42 AM ]
We received a range of guesses for our August natural mystery including muskrat, beaver, otter and raccoon—all of which are common on the muddy banks of the Minnesota River in Ft. Snelling Sate Park. Congratulations to Bren White and our generous patron Mike Holtz who correctly identified the species and which foot of four left this particular track.

This is the right front track of a river otter, This is the right front track of a river otter, Lontra canadensis.

As Mike shares:
"At first glance it looks like raccoon, but I think the carpal pad registering at the bottom of the track is helping tip it towards otter. The size is right, and the location certainly fits for otter."

Mike is exactly right here. And as he points out, the carpal pad is a key clue. Let's go through some of the other possibilities and see how we can distinguish this track from each:

Raccoon palm pads are more fully fused than mustelid palm pads and show less definition. The leading edge of the palm usually forms a smooth arc, rather than showing distinct lobes. In this track we can see several distinct, round palm pads. Raccoons do not have a separate carpal (heel) pad, seen in this track. Raccoon toes tend to register more uniformly along their length, and rarely show a bulbous tip.

Beaver have five toes on their front feet, but their toes taper from the palm to the tip, rather than appearing bulbous at the end. Their nails are more stout (they are a burrowing animal), and they have a different arrangement of pads. As in other rodents, beaver front feet have two heel pads. One of these is a carpal pad, and the other is the metacarpal pad at the base of toe 1. These two pads register roughly side-by-side and have a similar size and appearance. In this track, the metacarpal pad at the base of toe 1 is fused with the palm pads and the carpal pad registers as a separate heel. Finally, while toe 1 on beavers is more developed than in many rodents and has a claw, it is still much less developed than the other toes.

Muskrat hind feet are smaller, lack well developed palm pads, and don't have any pads on their heel. Their toes are lack a bulbous tip and are more slender. Though the fringe of hair can make them appear wide, they typically appear widest at the base.

Most often, otter tracks do not show the length of the toe this clearly—but while uncommon, this presentation isn't exceptionally rare. In this track, the structure of the palm pad and the distinct heel pad are some of our clearest clues that we are looking at a mustelid track. The size, habitat, location, and crisp tracks showing no signs of fur on the foot leave us with otter as our best candidate.

Congratulations again to Bren & Mike, and thanks to everyone who sent in guesses!


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