September 2025 Natural Mystery Answered

Last month's Natural Mystery was a special kind of challenge. I had never seen this track presentation before in any species, and didn't expect that any of you had either. A huge congratulations to Maria Wesserle for sorting through the clues to identify both who left this track and why it appears the way it does.

This is the track of a Bald Eagle (Haliaeetus leucocephalus) walking on the tops of its closed talons.

I'll turn it over to Maria here so she can walk you through her process:

"When I first looked at this photo, I was at a bit of a loss. I saw four marks on the sand in an arrangement that didn't make a lot of sense to me. I started by considering all my options: could this be a mammal, bird, herp, or invert? Or possibly an abiotic process or a human? But the more I looked at it, the more confident I felt that they were four claw marks from one foot: the sharp indentations in the ground arranged in an inverted J-shape seemed too orderly to be abiotic and didn't match hand or foot morphology for humans.

My next step was to consider animals that live in northern Wisconsin that might leave a similar track shape and that register heavily on the claws. Porcupines and snowshoe hare can both leave prints of only their claws, but the spread of the claws in the photo is too large for both species (about 4.5" long and 3" wide.) Furthermore, the morphology doesn't quite match. Then I noticed that when you draw lines between the claw marks you can create a K-shape, which made me wonder if this could be a great horned owl. Though on the large side, it is within range according to Jon Poppele's Bird Tracks book. But why weren't the toes registering?

Looking closer at the photo, I realized that I could make out the shape of talons. The four impressions were not created by dragging claws, but by sharp raptor talons pressing directly into the sand. The shape of each talon indicated that they were pointing toward each other, which means the raptor must have been holding onto a prey species. This is why the toes didn't register!

Given the large size and location along a river, I added osprey and bald eagle to my list of potential candidates. I couldn't find osprey tracks listed in any of my books, but did find a research grade photo on iNaturalist that showed a 3" length for osprey—much smaller than what we see here. Bald eagle tracks are 6-8" in length according to Poppele, which is larger than the track in the photo. However, this large raptor foot is grasping a prey species; the size of the track registers as smaller than the actual foot, due to the curving toes and claws in this position.

We are therefore looking at the track of a bald eagle grasping prey in its talons—probably a fish. I expected the fish's body to be imprinted in the sand, but I don't see any clear evidence of this. There is some disturbance on the right side of the photo that might possibly be from the fish's tail flopping around. Regardless, we can clearly see the impression of the talons from the flexed foot of the eagle."

This is exactly right. Nicholas Wazeegale found this track in the field and he and I worked out the story. The eagle was indeed holding a fish in its left foot, which is why it was walking on its talons. Its right foot was also leaving faint tracks. Maria is also spot-on about why the track measures smaller than the parameters given in the tracking literature--these measurements all include the length of the claws extending out from the tips of the toes. But if you compare the life-size illustration from Bird Tracks, you can see that this track is exactly the size of a Bald Eagle track measured toe-tip to toe-tip.

Congratulations again to Maria, and big thanks for sharing her process with all of us. And thank you as always to everyone took a crack at untangling this exceptionally challenging Natural Mystery.