October 2024 Natural Mystery Answered

We had a great response to last month’s Natural Mystery. Thanks to everyone who submitted an answer—especially to all of you who shared the details of your process. Congratulations to Blake Southard, Alan Holzer, Erin Anderson, Collin Arnett, and Kirsten Welge for correctly identifying the species that left these prints. A further shout-out to Blake, Alan, Collin and Kirsten for identifying which foot made the track at the 3 ½” mark on the ruler.

These are the tracks of a painted turtle (Chrysemys picta), which is sometimes colloquially (and confusingly) referred to as a “mud turtle.” Most commonly, the colloquial name “mud turtle” is used for members of the genus Kinosternon, which belong to a different family.

Erin starts us off with her first impressions:

“When I first saw this picture, I was immediately drawn to turtles as the obvious candidate due to the sharp claw marks, the shape of the front heel pad that is wider than long.”

Alan points to the “wide trail and closely-spaced tracks” indicating a turtle, while Collin and Kirsten note the pebbly texture typical of clear turtle tracks.

Erin then noted that this leaves us with the question “which turtle?” Alan points out that “the most common turtles in this spot are painted and snapping turtles, though there are many other possibilities as well.” Erin looked up common turtles in the Minnesota Valley National Wildlife Refuge and came up with a slightly longer list including snapping, false map, painted, smooth softshell, and spiny softshell. A search on iNaturalist for turtles observed in the Refuge adds pond slider, northern map turtle, and Blanding’s turtle to our long list.

Referring to Filip Tkaczyk’s Tracks and Sign of Reptiles and Amphibians, Alan notes that “snapping turtle front tracks [are] much more angled in toward the center of the trail, and also [show] more variety in the size of scales on the ball of the foot. Painted turtles have an oval shape to the front foot pad, with the front feet pointed straightforward as they walk, and more evenly-sized scales on the bottom of their feet.” A quick glance at Tkaczyk’s entries for softshell turtles shows that these highly aquatic species have quite different foot morphology than we see here. Tkaczyk also notes that pond slider tracks and trails are typically larger than we see here and that, like snapping turtles, their front feet tend to pitch in between 45 and 90 degrees.

That narrows our list down to painted turtle, false map turtle, northern map turtle, and Blanding’s turtle. Collin takes a simple and direct approach, noting “common being common,” and the morphology being a match, these are most likely painted turtle tracks. This may be as good as we can do for now. Tkaczyk does not include any information about false map, northern map, or Blanding’s turtles.

Both Collin and Erin also pointed out that the illustration of painted turtle tracks in my Animal Tracks of the Midwest guide are a remarkably good match for the tracks in this photograph. That is even more true than they may have realized. This photograph, and others I took of this trail, are the references I used to create my illustrations of painted turtle tracks.

Which Foot

The track immediately below the 3 ½” mark on the ruler is a right front. Kirsten notes that it "on the right side of the trail, and shows a squat, oval, pebbled pad. Five fine claws register separately above the pad.” Painted turtle hind tracks are longer than they are wide and only have claws on four of the five toes. The outermost toe is shorter than the others and lacks a claw. Collin uses this feature to distinguish the left and right sides of the trail, noting that the hind track just below the 5” mark on the ruler “has a recessed fifth digit to the outside of the trail which makes it a right-sided track.”

Age & Sex

It may be possible to determine the sex of mature painted turtle from their tracks. My interpretation is that these are the tracks of a mature male—and that was my interpretation when seeing the animal as well. Alan was on the right track when he noted that, “for painted turtles, males have very long claws on their front feet, and are somewhat smaller than females as adults."

Getting a rough sense of the size of a turtle from its trail is simple—large turtles take longer strides and leave wider trails. But converting trail measurements into precise body measurements is not so straight forward. Stride length and trail width will vary with substrate and with speed, and different types of turtles have different limb postures. One thing we can do is compare the measurements of this trail to Tkaczyk’s published parameters.

I measure the stride length in this photo as averaging roughly 8 cm or 3.1 in, putting it toward the lower end of Tkaczyk’s published range of 2.3–5.5 in. The trail width is roughly 11.3 cm or 4.3 in, which is again toward the lower end of Tkaczyk’s range of 4–6.6 in. This suggests a smaller individual.

Front tracks measure 1.7 cm (0.68 in) wide, which is smaller than the smallest measurements Tkaczyk reports for front track width (0.7–0.85 in). Hind tracks are 1.55 cm (0.62 in) wide, which is near the bottom end of Tkaczyk’s range (0.6–0.75 in). These measurements again suggest a smaller individual.

Front track length, on the other hand, measures a minimum of 2.3 cm (0.9 in) and perhaps as long as 2.9 cm (1.15 in). Even the minimum measurement is longer than the upper end of Tkaczyk’s range of 0.6–0.8 in.

Taken all together, these measurements suggest that these are the tracks of a relatively small adult painted turtle with relatively long claws—indicative of a sexually mature male.

Tkaczyk (p 324) notes that the claws on a male painted turtle may make up half of the total track length—which appears to be the case here. We can contrast the way the nails show here with how they appear in Tkaczyk’s photos and Seb Barnett’s illustrations, which show the tracks of female painted turtles.

Congratulations again to Blake, Alan, Erin, Collin, and Kirsten! And thanks again to everyone who submitted an answer to this Natural Mystery.

Resources:

Frazer NB, Greene JL, Gibbons JW. 1993. Temporal Variation in Growth Rate and Age at Maturity of Male Painted Turtles, Chrysemys picta. The American Midland Naturalist. 130(2):314–324. doi:10.2307/2426130.

Detailed information about plastron size and claw length in painted turtles: The longest foreclaws on mature females are typically 6-8mm in length, while the longest foreclaws on mature males are typically 10-13mm. Plastron length ranges from 75-125 mm in adult males, and from 100-145 mm in adult females.

Tkaczyk F. 2015. Tracks & sign of reptiles & amphibians: a guide to North American species. Mechanicsburg, PA: Stackpole Books.

Female vs Male Eastern Painted Turtles (video)

https://www.youtube.com/watch?v=Xc0MqM1UK3E

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