9/18 Turtle Weather

 

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Female Box Turtle trying to avoid me at BCSNP

What’s a Box Turtle’s favorite weather? I’m guessing it’s two days (at least) of steady light rain, to saturate everything and bring out the snails and earthworms. Last Wednesday’s weather was close to ideal; I was out early scouting the site of an invasive plant workday, when I almost stepped on the first turtle. My foot slid off his wet slippery carapace; the boxie quickly retreated into his “box” and stayed there. He was a large chunky turtle, with a brightly outlined pattern on his carapace, and unique fine mottling below.

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He was  entered in my data book as #205 (of all recorded box turtle sightings since 2013). As a middle aged male, he is part of the most commonly observed demographic at BCSNP. Within the next hour, as the rain got more steady, the turtles just kept appearing – good turtle weather was here. Even in places where they’re abundant, Box Turtles can lie low for weeks or even months, particularly if conditions are hot and dry. Visiting only during such times, one might mistakenly assume no boxies lived there. Such was the case at a very large MSD construction site on the edge of BCSNP, where (unsurprisingly) a biological survey turned up none. Fourteen Box turtles were later rescued from the site over the course of the summer before construction started.

The next turtle I encountered was also a large male, but visually quite different from #205.

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As  you can see in the pic of his carapace, the edges are flared and scalloped like a pie crust, and there’s good bit of wear on them. Though his coloration is duller and darker then the first turtle, like wet paint it appeared brighter in the rain. This helps explain why I was able to spot so many turtles on one rainy morning.

The third Boxie I spotted was a young female. Females are often duller in coloration than males; sighting #206 was a small, plain looking turtle with a bright plastron (underside) pattern.

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The next turtle (these sightings were about a half hour apart) was also a female – a very good sign for the population. The green dot on the rear of her carapace indicates she has been observed before.

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Though biologists aren’t sure why, there is a “skewed” gender ratio in many Box Turtle populations. Males often outnumber females, and the data I’ve collected at BCSNP follows this trend. Male turtles in this forest seem to  outnumber females by almost 2:1!

A mechanism called Temperature Dependent Sex Determination, or TSD, determines what gender a baby turtle will be, with more males produced at lower temperatures. Woodlands such as BCSNP, with a mostly closed canopy and understory infested with large Bush Honeysuckle, tend to be shady and cooler at ground level. So it’s possible that under such conditions Box Turtle nests would produce a higher number of male turtles. But if females venture out of this shady environment to seek warmer nest sites they’re at risk from mowers and cars, again resulting in fewer female turtles. Sound like a turtle catch-22?

Another previously marked turtle was spotted, as the rain really picked up. This large male was possibly older than the others, judging by the wear on his carapace. (Apologies for the poor image quality – blame the rain and dim lighting).

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Every Box Turtle has a completely unique pattern. A big reason I’m fascinated by turtles is simply this – each new sighting is a chance to see yet another randomly generated variation on a theme. All the turtles in this post live in a tiny part of a tiny fragment; though they look very different from each other, they’re likely related. How could they be so varied in appearance? Research on Box Turtles has shown that some individuals will make make long distance journeys out of their home range, for reasons unknown.  It’s one way new genes are introduced in a mostly sedentary population. And in an urban forest like BCSNP there’s also the issue of intentional releases of turtles from other places.

On a completely different note – Where does a turtle go when you turn your back?  Once I’ve spotted a turtle, I’ve learned not to walk away to get my data book if it takes longer than 10 seconds. Otherwise the turtle will be gone. The little female in this post’s opening pic lives near a spring, where I’ve seen her many times. I saw her again last Wednesday; after taking her picture for the data book, I walked off for a couple minutes. Returning to see if she was still there (she was not), I decided to do a search. Turns out she had not gone far, but wedged herself into a hiding place behind a tree trunk. Box Turtles live in such a small home range they can be intimate with its every feature – when sensing a threat, the closest fallen log is where they head to.

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Her underside pattern is quite striking and not exactly “cryptic”; it’s interesting to speculate about what purpose the plastron pattern could serve, as it’s in a place that’s rarely exposed.

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If you’ve made it through this post, you’re likely  weary of looking at pictures of Box Turtle shells by now. So let me offer this final pic…

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The fruits of Jack in the Pulpit are ripe now, and can be startlingly bright on the shady forest floor. There seems to be an increase in the number of plants each year (deer don’t eat them). However, Box turtles eat the berries and are helping spread them around.  How do they find them? Turtles, like birds, have great color vision and are very good at seeing shades of red in particular. For the reason why, check out this research:

http://www.cam.ac.uk/research/news/red-gene-in-birds-and-turtles-suggests-dinosaurs-had-bird-like-colour-vision

And if you want to see Box Turtles, hit the trail on a rainy day.

 

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