The turtle lives 'twixt plated decks
Which practically conceal its sex.
I think it clever of the turtle
In such a fix to be so fertile.
-Ogden Nash-
Today I’m going to talk about Eastern box turtle reproduction. Some of what I will describe here comes from textbooks on the subject that I have in my possession, so I will attempt to strike a balance between being unreadably scientific and grossly oversimplified.
First of all, in part because Eastern box turtles are comparatively small, they typically do not lay very many eggs. Unlike a sea turtle, which can lay over 100 eggs in one session, the average size of an Eastern box turtle’s clutch of eggs is 4-6, although the largest clutch on record is 11 in one egg laying/nesting session.
Although mating activity is somewhat seasonal in nature, it has been my experience while observing the turtles here that they will mate when the opportunity arises. Their activity usually settles down during the nesting season and the heat of the summer, but they will grab the opportunity to mate during a cooling mid-summer rain shower. I have witnessed my turtles mating immediately upon emerging from hibernation, and also into the autumn months.
In the wild, Eastern box turtles mating encounters are somewhat haphazard, in that they mate when they happen to encounter one another. There is no evidence (at least not yet) that scent, or pheromones play any kind of a role in finding a mate. But, because they can and do congregate around seasonally available food sources, this may be one reliable way of finding a mate. So go ahead and think of that blackberry patch as a sort of singles bar.
Eastern box turtle courtship behavior is typically divided into three phases, and if you are not watching carefully and paying attention to certain nuances of behavior, it is easy to mistake this behavior for aggression, and vice versa.
First, the male will circle, shove, and bite at the carapace of a female. When a male approaches a female, he straightens his legs so that he ‘stands tall’. The female usually retracts in to her shell, so the male may even roll her over a few times.
Then there follows what is referred to as a preliminary mounting. When the male does this, he immediately uses those thick curved claws on his hind feet to hook himself on to female’s plastron.
Until this point there is little difference between courtship and aggression: males will do these same things to other males that they want to challenge.
The male will peck at her head and carapace, sometimes to the point of doing some damage. Many females have had their carapaces chipped by overly enthusiastic males. It is not always a pretty process. Captive males can really harass females due to the fact that they are kept in confined quarters, and I have found that I have had to, on occasion, put one or two of the boys here in ‘solitary’ for a day or three.
If the female is receptive, she will use her hind legs to secure his: they link legs, as it were. His hind feet will shift forward, and she will clamp down her plastron.
The final phase is actual coitus. For copulation, the male will actually lean back, to a point where he is vertical, or perpendicular to the ground, with the back edge of his carapace touching the ground. By leaning even further back, and then returning to this vertical position, intromission can occur.
You may never think of that airline seat tray the same way again.
On occasion, the females will even move about a little, dragging the males along with them!
Time for some somewhat technical stuff:
Sexual cycles inbox turtles are seasonal: males produce spermatocytes in the early summer, and spermatozoa are present throughout the year.
In females, the oogenic cycle begins in mid to late summer, follicle accumulate in the autumn, with ovulation occurring in May, and nesting and egg laying occurring any time from late May in to July.
The period of inactivity during hibernation may play a vital role in hormone production, but this aspect of the reproductive cycle is not fully understood.
A very interesting feature of Eastern box turtle reproduction is a “back up system” that females have. Because there is no guarantee that they will find a mate and breed every year, they can actually store viable sperm for up to 4 years. Yes, you read that correctly: they can lay fertilized eggs for several years after their last mating, albeit with diminishing returns. The sperm is ‘stored’ in albumen secreting ducts in the oviducts. These ‘storage’ ducts are restricted to one specific area of the oviduct.
So, unlike humans, one cannot count the days after sex to calculate when the baby will be due...
Back to the cycle:
Sometime in late May or early June, female turtles will begin their search for a suitable nesting site. Sadly, this is when many females turtles are killed while trying to cross roads in search of a nesting area. Unlike other species of turtles, Eastern box turtles do not necessarily return to the same area year after year, nor will you typically find gravid females congregating in one area to dig their nests, the way more aquatic species might.
Gravid females often travel considerable distances (up to several hundred meters) to find a nesting site. Frequently the nesting site is in a somewhat open area where there is plenty of sun, and little in the way of obstructing tree roots and large rocks. Frequently, Eastern box turtles nest in meadows, as grass roots are of little consequence when digging a nest.
For the most part, nesting begins in the early evening, and is typically completed well after dark. If soil conditions are unfavorable (hard clay, stony), the process may take all night or the female may even give up and try again the following night. If conditions are favorable (soft loamy soil with no obstructions), the entire process can take as little as 3 hours. Often nest digging begins shortly before, during, or after a rain.
The nest cavity, which is dug entirely with the hind feet, is flask shaped, with a comparatively narrow opening about 2 inches in diameter and a main cavity somewhat larger, depending on the size of the female and the length of her legs and usually measures about 3 inches from top to bottom. It can take several hours for her to dig the nest to her satisfaction.
When digging is complete, she lays the eggs, one at a time, carefully positioning each one within the nest with her hind feet. Based on my own observations of the turtles here, the first eggs are typically maneuvered forward to the ‘front’ of the nest, later eggs go to the rear, and any that do not fit in to the bottom of the nest will sit on top of the earlier eggs.
The egg-laying phase of the operation only takes a few minutes: for an average sized clutch, about 15 minutes.
Then begins the nest covering. The first thing the female does is she reaches waaay around with a hind leg and grabs toefulls of debris: the first material out is often the first material back in. bits of leaves or grass that were on the surface are deposited on top of the eggs. What this does is allows for an airspace between the eggs and the nest ‘cover’ which is essentially a tightly packed ‘plug’ of soil that fills the neck of the nest. The plugging process involves loads of tamping and treading, almost a little dance, with toes curled under, or with heels, or even knees. The very final touches are even done with the plastron.
Once the covering is completed, the nest is often further camouflaged, with loose dirt and debris swept over the nest. Often it is impossible to detect a nest once the final touches have been added, although sometimes they do leave evidence:
When this is all finished, the female may leave the area entirely, or stick around to rest and possibly guard the nest, but that is the extent of her maternal care.
