Friday, October 10, 2003
When and where seen: Three hatchlings were seen by Betsy Fell, on September 29, on the dirt track down to the garden plots at Foss Farm; also two hatchlings on September 11 in the parking lot at the Town Hall, where one had been run over. The other is the specimen in the photograph. You are more likely to spot the adults in late May or June as the females seek out an area to lay eggs.
Distinguishing characteristics: The snapper is the largest turtle found in Massachusetts. Adults have tipped the scale at 60 pounds. The carapace or topside shell may reach 18 to 20 inches long. It is gray to black and could have a green tinge due to algae. The back edge of the carapace is jagged. The head is large, and the neck and saw-toothed tail are long. The underside shell, or plastron, is relatively small, cross-shaped and yellowish. The claws are long, strong and curved. The hatchlings are perfect miniatures of the adults but a lighter color. The hatchling in the photo was about three inches long including head and tail. The carapace was about an inch long.
Habitat: The preferred habitat is shallow, marshy backwaters and ponds with a muddy bottom and lush aquatic vegetation but just about any permanent water source with sufficient food will do. Snapping turtles are omnivores. They eat whatever animals they can catch and a large quantity of various water plants.
Snapping behavior: The common name describes the method of seizing prey. Humans are not prey but are subject to menacing defensive behavior and potentially a nasty bite from a snapper, on land, if it feels cornered or threatened. Adult snappers are found on land in the nesting season, and at other times if they are looking for a new pond. If you see a snapper on land and watch it from several paces behind, it will probably continue its activity as if you weren't there. People swimming are at little risk from snappers since the turtle will swim away if disturbed by humans.
Napping behavior: Snappers will bask in the sun on logs and fallen trees in their ponds but you are more likely to see this behavior from other species · like the painted turtle. Snappers engage in "aquatic basking" in shallow water. Much of the carapace and the snout will be out of the water. Basking raises the body temperature which helps with digestion and general agility. In the winter, they burrow into the mud at the bottom of the pond for a long nap.
Nests, eggs and hatchlings: Snapping turtles normally select sandy areas for their nests. Riverbanks, shoulders of roads, and lawns are common sites. A female snapper will dig several false nests before selecting the final nest. My garden is visited almost every year in early June by a large, slow, lumbering, prehistoric-looking creature that uses Murphy's law of nest location. She chooses the places I least want her to dig · maybe because these spots are where I have recently planted something and the digging is easy. Snappers lay a single clutch of typically around 30 (but sometimes up to 80) spherical eggs and then return to their pond. Predators, especially skunks, destroy nearly all the nests. The remaining eggs hatch in three to four months so we would expect to see hatchlings in August and September. The gender of the hatchlings is correlated with incubation temperature during a particular stage of development. Researchers have found that a temperature of 58 degrees F results in all females; 73 degrees results in males; raising the temperature to 77 degrees results in all females. (This is probably being studied in parts of China.) The little hatchlings seem to have a secret GPS system that lets them find their way to a pond sometimes as far away as a quarter mile. They take approximately five to seven years to reach breeding age.
References: Leo P. Kenney and Matthew R. Burne, A Field Guide to the Animals of Vernal Pools; Thomas F Tyning, Stokes Nature Guides, A Guide to Amphibians and Reptiles; University Of Michigan.
Submissions for the Biodiversity Corner are encouraged from everyone. You can write the column yourself or tell me what you saw and I will write it. The only requirements are that the subject exists in the wild and was seen in Carlisle. Send a note to Kay Fairweather at 392 School Street, Carlisle MA 01741 or to firstname.lastname@example.org.
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