July 2024 Natural Mystery Answered

Everyone who offered an answer to last month’s Natural Mystery identified it as a front track from a small rodent—and it is indeed. We had a range of guesses about which small rodent left this particular print, however. Congratulations to facilitators Kirsten Welge and Maria Wesserle who correctly identified the species that left this print, as well as the side of the body.


This is the left front track of an eastern chipmunk (Tamias striatus).


Kirsten will start us off with these observations of the track:


To this, Maria adds this note:

"I think that in this photo, we can see a blurry shape below the palm pads and beneath the small gray rock, which I am interpreting as the print of two heel pads."


Maria measured the track as about 2.3 cm (just over 7/8”) long by 1.5 cm (not quite 5/8”) wide. Kirsten gives the same width, but measured the length at just 1.6 cm (5/8”), which is the length of the track without the heel pads.


This is the typical morphology of a rodent front track. Based on the size, Kirsten and Maria narrow the list of candidates down to a small sciurid (a chipmunk, flying squirrel, or red squirrel), or an Old World rat. The track is too large to be from a mouse or vole, and too small to be from a gray squirrel.


Maria notes that the morphology is not a good fit for a rat, writing “rat tracks have a wide splay, whereas these toes point more-or-less forward.” Kirsten concurs, noting that “rat outer toes would splay to nearly a 180° angle.”


Maria compared her measurements to Elbroch’s parameters, writing:

“Elbroch lists red squirrel front tracks as 2.5 – 3.2 cm long by 1.4 – 2.5 cm wide. So this would be a bit small for a red squirrel. Elbroch lists the range for Eastern chipmunk as 1.9 – 2.5 cm long by 1.1 – 2.2 cm wide, which fits this track perfectly.”


She continues by noting:

“Flying squirrels aren't likely to be hanging out under a bridge, but I would also expect them to have slightly longer toes. Furthermore, they have more fur on their feet, which contributes to a blurrier track appearance. Also, their nails are shorter and don't always register, whereas chipmunks nails tend to be prominent in tracks. I therefore believe this is Eastern chipmunk.”


Similarly, Kirsten states:

“The overall blockiness of the foot, chunkiness and size of the palm pad, and placement of carpal pads close to the palm indicate this is a chipmunk. Flying squirrel tracks show longer toes, a more delicate and proportionally smaller palm pad, and carpal pads placed further away from the palm pad.”


And this is indeed a chipmunk track.


To determine which foot, Maria writes:

“To differentiate left from right, we might look for the vestigial toe 1, but it's not clear in this track. We can also look to the curve of the track, which point inwards. This tracks curves to the right, which would make it a left front.”


While Kirsten adds:

“As with humans, chipmunks have different size gaps between their digits. From largest to smallest: T1-T2, T4-5, T2-3, T3-4. The vestigial T1 is not present on this track, but the largest gap is between the leftmost toes – indicating those toes are T4-5.”


I will also point out that toe 3 in this track appears longer than toe 2. This is typical morphology for ground squirrels--the tribe to which chipmunks belong. This feature is more subtle in chipmunks than in many of the more highly fossorial ground squirrels, but may be visible as it is here. From what I have seen, flying squirrels seem to have slightly more symmetrical tracks, with toes 3 and 4 appearing the same length.

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