Most Snapping Turtles have entered hibernation by late October. To hibernate, they burrow into the debris or mud bottom of ponds or lakes, settle beneath logs, or retreat into muskrat burrows or lodges. Once a pond is frozen over, how do they breathe with ice preventing them from coming up for air?
Because turtles are ectotherms, or cold-blooded, their body temperature is the same as their surroundings. The water at the bottom of a pond is usually only a few degrees above freezing. Fortunately, a cold turtle in cold water/mud has a slow metabolism. The colder it gets, the slower its metabolism, which means there is less and less of a demand for energy and oxygen as temperatures fall – but there is still some.
When hibernating, Snapping Turtles rely on stored energy. They acquire oxygen from pond water moving across the surface of their body, which is highly vascularized. Blood vessels are particularly concentrated near the turtle’s tail, allowing the Snapper to obtain the necessary amount of oxygen to stay alive without using its lungs.
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Female Snapping Turtles spend a lot of time and effort finding suitable sandy soil in which to dig their nest and lay their eggs. Some turtles have been found laying their eggs as far as a mile from the nearest water source. Once she has laid her eggs and covered them with soil, the female snapper returns to her pond, leaving her eggs to hatch on their own, and the hatchlings to fend for themselves.
It is estimated that as many as 80 to 90 percent of all turtle nests are destroyed by predators, weather conditions and accidental disturbances. Most of the damage is done by predators – skunks, raccoons, foxes, crows, among others. Most nests are discovered by smell, and most are raided at night. The fluid that coats the eggs, that is lost by the mother during egg laying or is lost through breaks in the eggs, produces a smell that is easily detected by predators. While a majority of nest raids happen within the first 48 hours of the eggs being laid, studies have shown that predation occurs over the entire incubation period (June – September). The pictured Snapping Turtle nest was dug up and the eggs consumed 10 days after they were laid.
If you are aware of a spot where a turtle dug a nest and laid eggs, you can try to protect the nest from predators by placing either a bottomless wire cage or an oven rack over the nest site, and putting a heavy rock on top. The tiny hatchlings will be able to escape through the openings but hopefully, if the rock is heavy enough, raccoons and skunks will become discouraged and give up trying to reach the nest.
The next Naturally Curious post will be on 7/5/17.
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In June, mature female Snapping Turtles leave their ponds in search of a sandy spot in which to lay their eggs. (Capable of storing viable sperm for up to three years, female snappers do not necessarily mate every year prior to laying eggs.) Once this prehistoric-looking reptile locates a suitable location she slowly scoops one footful of earth at a time up and to the rear of her, alternating her left and right hind feet. If the soil is dry and tightly packed, she will urinate on it in order to facilitate digging.
Hole made, she proceeds to slowly lift her body and release ping pong ball-sized, -colored and -shaped eggs, usually one at a time, but occasionally two, into the hole beneath her. Down she comes for a minute or two of rest, and then up she rises again to release another egg. She does this anywhere from 20 to 40 times, a process that can take up to several hours, depending on the number of eggs she lays. Then her large, clawed hind feet slowly begin to scrape the two piles of soil she removed back into the hole, one foot at a time, until the eggs are covered, at which point she tamps the soil down with her plastron, or bottom shell. She then returns to the water, leaving the eggs and hatchlings to fend for themselves.
It is hard to accept that after all the effort that has been put into this act, studies have shown that 90 percent or more of turtle nests are raided by the likes of raccoons, skunks and crows. For those nests that are not discovered by predators, the sex of the turtle that emerges from each egg is determined by the temperature it attained during a specific part of its development. Eggs maintained during this period at 68°F produce only females; eggs maintained at 70-72°F produce both male and female turtles, and those incubated at 73-75°F produce only males. The eggs hatch in September, with many of the Snapping Turtles emerging then, but in the northern part of their range, young Snapping Turtles sometimes overwinter in their nest and emerge in the spring. (Thanks to Chiho Kaneko and Jeffrey Hamelman for photo op.)
Opportunities to see turtles in winter are extremely limited, but a hole chopped in pond ice recently revealed a Snapping Turtle swimming in the water beneath the ice. According to Jim Andrews, Director of the Vermont Reptile and Amphibian Atlas(http://vtherpatlas.org/ ), most turtles don’t often burrow into the mud during winter. They need to take in dissolved oxygen from the water and there is not much available in the mud. Turtles take in oxygen through the linings of their mouths and sometimes thin-skinned, capillary-rich areas in their cloaca and armpits. Many turtles are just sitting on the bottom of ponds. They may use a rock, log, or maybe some leaves for a little protection from otters or other predators.
If the ice is clear, it is possible to see turtles swimming beneath it. Andrews suggests that the Snapping Turtle in the photograph is likely picking up an oxygen boost by using its lungs for a change. It may be four more months before it gets another breath of fresh air. (Thanks to Jim Andrews for post and Barb and Paul Kivlin of Shoreham, VT for photo.)
Duckweed (Wolfia sp.), a free-floating aquatic plant that possesses flowers which are said to be the smallest flowers in the world, is coating our mystery creature. The presence of this plant can indicate that there are too many nutrients in the water, especially nitrate and phosphate. On the plus side, Duckweed provides waterfowl, juvenile fish and other wildlife (including humans in Southeast Asia) with a protein-rich (40%) food.
Under this green coating is a Snapping Turtle, one of the largest freshwater turtles in North America. Most often encountered in June, when females leave their ponds to lay eggs, Snapping Turtles are infrequently observed at other times of the year. This is primarily due to their crepuscular and nocturnal habits as well as their tendency to spend a lot of time under water feeding on plants, insects, fish, frogs, small turtles, young waterfowl, and crayfish.
Found in most ponds, marshes, streams and rivers, Snapping Turtles are not aggressive towards humans. Their size is impressive (a full-grown Snapping Turtle’s top shell, or carapace, can measure up to 20 inches in length) but they shy away from human disturbance. Miniature versions with one-inch long carapaces can be seen this month as the young Snappers crawl up out of their subterranean nests after hatching from eggs laid in June and head for the nearest water.
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Although Snapping Turtles may mate any time between April and November, much breeding activity takes place during April and May. Snapping Turtle mating appears fairly aggressive, with the male chasing the female, grasping the posterior end of her carapace and then mounting her. He holds on to the edges of her shell with all four legs, often biting her head and neck while he inseminates her.
The female Snapping Turtle can keep sperm viable in her body for several months (and perhaps years). Thus, there can be multiple paternity in egg clutches and it may even be possible that a female’s eggs are fertilized in years when she does not mate. (Thanks to Jim Block for photo. To see a photo series of Snapping Turtles mating (and many other very fine nature photographs), go to http://www.jimblockphoto.com/2010/04/snapping-turtles/)