Instinct guides snappers, rewards predators
- John Lorson: The Rail Trail Naturalist
- June 11, 2021
- 1186
Life and death along the trail: In the top right, a female snapping turtle deposits a clutch of eggs in a shallow, excavated nest, which may take several hours, followed by the female covering the eggs and then leaving the site for good. In the bottom right, a single egg is all that remains of the nest after it was destroyed overnight. The tragic result can be seen in the photo on the left, with the raccoon, skunk, fox and mink high on the list of suspects.
When I wrote about turtles a little over a month ago, the mating season was just heating up, and if you remember one of the more fascinating nuggets from that column, you’ll remember heat plays a very important role.
Ambient temperature, or the warmth of the egg’s immediate surroundings, determines whether offspring develop as male or female. This phenomenon, known as “temperature-dependent sex determination,” is present in a handful of reptile species including both turtles and crocodilians (alligators and crocodiles).
The female snapping turtle is genetically programmed to seek a place with just the right temperature characteristics — not too hot in the day, not too cold at night — to yield a mixed bag of offspring. The optimum temperature is 70-72 F. An average lower than that will produce only females and above, only males.
What never ceases to amaze me is the fact that no turtle that ever lived was taught what the perfect nesting spot looks like or, in terms of temperature, feels like. Nesting behavior is built in to the animal’s genetic code. The same is true of birds. Think for a moment about the complexity of the hanging nest of a Baltimore oriole or of the incredible strength, weight and durability of an eagle’s nest.
The brain of each of those creatures comes filled with a set of instructions for reproduction, and if the instructions are complete and accurate, that animal is far more likely to be successful in producing viable offspring than fellow members of its own species. That’s what makes the species “better” as it moves through time.
Temperature, however, isn’t everything when it comes to hatching a successful turtle brood. In the presence of predators, concealment of a nest that will be entirely unattended is a hit and miss game. Just as no turtle has seen a nest built, neither has one hung around to see if the spot she chose went undetected and her eggs, consequently, remained unmolested for the duration of their incubation period.
Some nests win and some nests lose, and the only way the species improves its nesting abilities through time is the very simple fact each turtle came from a mother who somehow did it right.
Hopefully, the young turtles from this year’s hatch aren’t simply lucky and will carry with them a little something to help them get a leg up on nest predators. From what I’ve been seeing, the predators are presently winning the battle in a landslide.
In recent weeks during my morning rides, I’ve spotted nearly a dozen egg-laying snappers, and nearly every morning subsequent to the sighting I’ve found nests destroyed in the overnight hours. Granted, turtles don’t do a great job of “hiding” their nests. They merely excavate a shallow, frying pan-sized hole, deposit 20-40 leathery, round eggs about the diameter of a quarter, then scrape the soil from the hole back over the whole mess and get on with their lives. This does not bode well in an area ripe with predators hunting by sight or by smell.
A snapper nest jumps out of the landscape like a buffet warming tray to the likes of both aerial opportunists like crows and ground-bound hunters like fox, mink and skunk.
The most likely and effectively devastating nest predator in the area where I’ve been making my observations has been the raccoon. Imagine the joy with which a mother raccoon and her kits revel in the discovery of an unattended “basket” of free eggs. The results are both maddening and saddening, knowing an entire breeding season for that individual is effectively canceled in one meal.
Hopefully, a handful of nests will make it through the nightly assaults and the young snapping turtles, be they male, female or a balanced hatch of each, will make their way into the relative safety of the marsh to pass along their built-in survival smarts to a generation of their own offspring.
Remember, of course, to never disturb a turtle (or any other wildlife for that matter) as it goes about the business of reproduction. An egg-laying snapping turtle will allow you to watch all you like from a safe distance several yards away, but don’t get too close.
Remember, if you have comments on this column or questions about the natural world, write The Rail Trail Naturalist, P.O. Box 170, Fredericksburg, OH 44627, or email jlorson@alonovus.com. One also can follow along on Instagram @railtrailnaturalist.