As the spring and early summer heavy rains gave way to heat and drought, Box turtles were a little less active. On 7/30 I encountered this large male, one of the most strikingly patterned turtles I’ve ever observed. He was near the edge of the preserve and a busy road, and unfortunately rather boxed in (excuse the pun) between the road, the deeply channelized creek and open, mowed parkland. It leads me to wonder how he came to be in this little island of habitat – is it part of his home range or did he come here seeking a mate? If he wandered in from the forest, he had to clamber down a very steep bank, swim the creek, and climb back up the equally steep far bank.
This pic shows the carapace of the same turtle, also highly patterned. I understand the value of the great variety of Box turtle scute patterns on the upper shell – but why on the underside too? Science has not explained this to my satisfaction (and I have searched for studies). It remains a mystery why Eastern Box turtles have such strikingly varied, and often asymmetrical plastron patterns. If these turtles were spending a lot of time on their backs, it might make sense as camouflage – but even so the underside patterns are often considerably more bold and striking than those on top. The only time I have seen a Box turtle voluntarily exposing its plastron is during mating, when the male leans back to facilitate coitus.
The images above are a sampling of plastron patterns on Box turtles in this forest. Studying the pics closely, I realized that the posterior end of each scute or scale is dark pigmented. This dark pigment creates a pattern on each scute that often, but not always, has bilateral symmetry. It can be quite varied from turtle to turtle, ranging from very clear-cut pattern blocks, to more wavy or flame-like displays. The range of plastron patterns is quite a bit more diverse than those found on the carapace. When I encounter a Box turtle in this forest, I often can remember if I’ve seen it before by looking at the underside pattern.
Of the five Terrepene carolina subspecies found to the south and west, three are relatively dull and muted above, and mostly featureless below. The Ornate and Florida subspecies are very crisply patterned above and below in a more linear, symmetrical way, suggesting their habitat is relatively open and grassy. But none have the degree of variation, above or below, of the Eastern box turtle. There is however another North American turtle with a plastron puzzle – of the four subspecies of Painted turtle, only the Western subspecies has a colorful and varied pattern below. Conceivably this would communicate a message to other turtles swimming below it, yet the Eastern, Midland and Southern Painted turtle subspecies have dull pale undersides. Evolutionary biologist Jeff Mitton noted this difference and blogged about it:
Besides plastron patterns, other unique markers such as missing scutes, healed injuries, and bright pigmentation can help me remember if I’ve previously encountered a Boxie. I met the older male above on 9/8 in the mid morning – my notes say 86 degrees and “hot”. He pulled in his orange head when I approached, but the deep pigmentation and damaged scutes jogged my memory.
Sure enough, he’d last been recorded in 2014, and not very far away. That’s him sitting on my notebook.
On 9/21, another hot dry day, I came upon these two in the middle of the dusty trail. The female is wearing a transmitter, and it had apparently been reglued since there is dried epoxy on her carapace. They’re not mating yet – the male is just “courting”, which often consists of biting her on the head and the front of her shell. I left after taking the picture, so I can’t say whether they hit it off or not.
I had the good fortune this summer to see some relatively younger and older Boxies, in contrast to the mostly middle aged population. Older females, like the small one above with the very worn carapace, are particularly uncommon. The smooth condition of her shell and loss of pattern complexity are markers of advanced age. Unlike many of the females I saw this year, she was in the forest interior, far from any edges – perhaps a clue to her long survival!
The pic above shows her underside, equally worn and pitted by all the years of walking across the forest floor and navigating over and under obstacles. How old could she be? For a reptile with a lifespan analogous to our own, I would guesstimate her age at sixty to eighty years.
On the younger end, the two Boxies above appear to be less than ten years old. The orange pigmented one was only four inches long, and both have the blurry, still developing scute pattern and knobby ridge atop the carapace, that indicate an immature Box turtle. Young turtles are particularly vulnerable to predation since their shells are smaller and thinner, and easier for teeth to penetrate.
On 10/14, while cutting Bush honeysuckle near the creek with a few other forest stewards, I almost stepped on one of the most beautiful Box turtles I’ve ever seen.
His underside pattern was pretty amazing too.
And now for the numbers – I recorded 41 observations of Box turtles for 2019, making a total of 250 sightings over 7 years. None of these were found by searching, just encountered in the course of daily forest restoration work. There are a lot of turtles in this little forest, but as time goes on it’s clear that some turtles are being recorded multiple times. Some boxies just seem to be out and about more, in well traveled areas, so are recorded more often. The challenge is to compare the various sightings and determine just how many individuals there are. The gender ratio this year was 19 males, 22 females, and 6 turtles too young to sex accurately. Those six are a very hopeful sign for the future.
On 10/20, the last turtles of the year – proving that for male boxies anytime is mating season.