by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station
While walking my dog Swegen at Windswept Bog this past week, I noticed signs installed by the Nantucket Conservation Foundation reminding visitors that June is turtle nesting month. Within ten minutes I found a nesting painted turtle and a spotted turtle traversing the small dike roads between bogs. Swegen was pretty mystified by these little packages and is apparently almost scared of them, which is a good thing. At the Nantucket Field Station over the past two months, I have seen several nesting snapping and painted turtles. The Field Station and areas all over the island support a sporadic parade of successful and not as successful turtle hatchlings crossing our roads and driveways after escaping from their underground birth sites. They are “hightailing it” to the safety of nearby ponds and wetlands. The sight of a female turtle laboriously depositing eggs for an hour or more, covering them, and trudging back to the water may seem sweet and noble, but in reality is it the reptilian equivalent of leaving one’s baby in a basket on the doorstep of a church. Once she is done, that is the last she’ll see of her offspring. And the reality in the spring and summer is that, in spite of several road signs asking us to slow down, and the best intentions of drivers who stop to help them across, inevitably squashed turtles will be found on the roadside. What do those squashed turtles tell us?? Well, obviously, we are disrupting their travel routes, fragmenting their habitat, and that, when so moved, they will travel significant distances to lay eggs or find new digs.
There are three different species of turtles on Nantucket who all love to be near freshwater, the spotted turtle (Clemmys guttata), the painted turtle (Chrysemys picta), and the common snapping turtle (Chelydra serpentina). There is some debate as to whether we have any of the states’ other species such as the Eastern Box Turtle, a Species of Special Concern.
The Nantucket Conservation Foundation has conducted many years of interesting telemetry research on the spotted turtle, which has recently been delisted from the Commonwealth’s List of Endangered, Threatened and Special Concern Species. A description of their research is at http://www.nantucketconservation.org/page.php?section=2&page=current_research. They are examining the range and behavior of the spotted turtles and have been able to document some turtles that go quite a distance to travel between their various seasonal habitats. From the NCF website we learn that “The spotted turtle (Clemmys guttata) is a small, semi-aquatic, freshwater species of eastern North America. It is distributed from southern Ontario to Maine, south along the Atlantic Coastal Plain to northern Florida, and west to northern Indiana. Throughout much of its range, this species is considered threatened, endangered, or vulnerable, primarily due to degradation and fragmentation of wetlands, mortality from crossing roads and collection for the pet trade. In 2006, the spotted turtle was removed from the list of species protected by the Massachusetts Endangered Species Act. However, it is still illegal to collect, sell or possess a spotted turtle. Despite the de-listing of this species, the Nantucket Conservation Foundation believes continued monitoring of spotted turtles on Nantucket is warranted because island populations often face ecological challenges such as physical and genetic isolation from mainland populations, limiting migration and gene flow between populations. Results from research on Nantucket’s populations of the spotted turtle could potentially be applied to conservation and management of mainland populations that have become isolated due to habitat fragmentation.”
Turtles, a generic name for the group of reptiles which includes tortoises and terrapins, are reptiles most of whose body is shielded by a special bony shell developed from their ribs. All extant, or living, turtles are members of the order Testudines, which includes both living and extinct varieties of turtle. The earliest known turtles date from 215 million years ago, making turtles one of the oldest reptile groups and a more ancient group than lizards, snakes, and crocodiles. Of the many species alive today, some are highly endangered. There are two major groups of turtles: sea turtles, which grow to large sizes and live in the oceans in the temperate and tropical regions of the earth, and fresh-water turtles. Fresh-water turtles which spend the majority of their time on the land are generally called tortoises. Fresh-water turtles are generally much smaller, ranging in size from a few centimeters to a few feet long. All turtles have a protective shell around their bodies. The top part of their case is called the carapace, the underside is the plastron, and the two are connected by the bridge. Even though they spend large amounts of their lives underwater, turtles are air-breathing reptiles, and must surface at regular intervals to refill their lungs with fresh air. They also spend part of their lives on dry land.
According to this excellent Massachusetts Division of Fisheries and Wildlife turtle tip site http://www.mass.gov/dfwele/dfw/nhesp/conservation/herps/turtle_tips.htm), Massachusetts has ten native terrestrial and aquatic turtles (not including sea turtles) and six of those are listed under the Massachusetts Endangered Species Act (MESA). In addition, Massachusetts has one widely distributed, introduced (non-native) species (the red-eared slider which we’ll learn more about shortly).
The reason we are seeing some many turtles over the past two months is that they are moving out from their winter mud holes to lay eggs and eventually occupy some warmer often drier meadows and fields and enjoy the summer. The scientific term for animals that lay eggs with a shell from which offspring emerge is oviparous from the Latin oviparus, or ovum “egg” plus the stem of parere “to bring forth.” Not only do many reptiles fall into this category, but also birds and even platypus are oviparous. Most turtles lay eggs once every year or every other year and the mortality rate for young hatchlings is quite high. Turtles also take a while to reach sexual maturity and may live many years (from a minimum of twenty years to up to 100 years for box turtles). Peak nesting season is during the month of June. Females nest in fields or residential yards, areas where the nest will get sunlight throughout the day to incubate the eggs. They prefer patches of bare sandy soil when available. If you find a nesting female the best thing to do is to keep people and animals away from the area until she’s done nesting, which can take several hours.
Snapping Turtles (Chelydra serpentina) mate and lay eggs from April through November, with their peak laying season in June and July. The females can hold sperm for several seasons, which greatly increases their ability to lay eggs without needing to find a male each year. Socially, that may not be the best practice. Females travel over land to find sandy soil in which to lay their eggs, in some instances traversing a mile of terrain. After digging a hole, the female typically deposits 25 to 80 eggs each year, guiding them into the nest with her hind feet and covering them with sand for incubation and protection. Incubation time is temperature-dependent, ranging from 9 to 18 weeks. In cooler climates, hatchlings may overwinter in the nest, although that doesn’t always insure survival in a frigid winter.
The painted turtle (Chrysemys picta) is the most widespread native turtle of North America. It lives in slow-moving fresh waters, from southern Canada to Louisiana and northern Mexico, and from the Atlantic to the Pacific. Although they are just as susceptible to habitat loss and road side squashing, they have become the most abundant turtle in North America due to their ability to live in human-disturbed settings. The turtles mate in spring and autumn; between late spring and mid-summer females dig nests on land and lay their eggs. Painted turtles may nest two or three times per year, at two to three week intervals as opposed to spotted turtles that only nest once a year. Painted turtles engage in an interesting courtship ritual in which the male uses his long claws, “palms” facing outward, to stroke the female on the cheeks and neck (no definite literature on whether they prefer Barry White or Sade). The eggs of painted turtles in Massachusetts are usually deposited from June to mid-July; the average clutch size is 5-6 eggs; and hatching occurs from mid-August through September after a 70 to 82 day incubation period (http://www.bryoecol.mtu.edu/chapters_2011/15Reptiles.pdf ). Hatched turtles grow until sexual maturity which is 2–9 years for males and 6–16 for females. Adults in the wild can live for more than 55 years. They are dependent on the sun for warmth, basking for hours at a time and hibernate during the winter, in fact, they sound a lot like our summer beachgoers. Here on Nantucket some painted turtles will overwinter in their eggs; the first tiny hatchling I saw this year appeared in later March and was the size of a quarter.
Confounding the spotted turtle’s (Clemmys guttata) ability to proliferate is their small size and small clutch (egg) size; the spotted turtle may lay only three to five eggs in a nest. Spotted turtles are a shallow-water turtle and they prefer a soft bottom substrate with both submerged and emergent vegetation. Therefore, boggy ponds, fens, and sphagnum seepages which can be found around Nantucket provide suitable habitats. In the spring, the turtles sometimes travel to seasonal or even more permanent pools, then search for nesting sites which can vary from sphagnum patches to loose or sandy soil in open areas, fields and meadows. Their nesting season occurs in mid to late June (varies slightly depending on latitude); they prefer to lay their eggs at night and may take up to 8 hours to dig a site and deposit their eggs. Not a lot of research has been done on spotted turtle nesting but the few I could find say that the size of the female determines the number of eggs and the number of times they can nest. In a paper by Litzgus and Brooks (1998), the mean clutch size was 5.3 eggs in Ontario, while Mass Audubon lists 3-4 eggs on average for spotted turtles in Massachusetts. As predicted from optimal egg size theory, clutch size was positively correlated with female body size, whereas egg size was independent of female body size. According to Mass Audubon, spotted turtles eggs experience a 70 to 83 day incubation period and then hatch in late August or in September.
You may recall that at the Nantucket Field Station lab we have our resident (and extremely popular) interloper turtle, a red eared slider named Trawalney. The red-eared slider Chrysemys scripta elegans (formerly known as Trachemys scripta elegans) is a semi-aquatic turtle belonging to the family Emydidae. The “slider” part of their name comes from their ability to slide off rocks and logs and into the water quickly. These turtles are introduced into the wild from the pet trade and have become the most entrenched invasive turtle species in the United States and the most widely invasive reptile species in the world. Although native to the southern states, these turtles have taken over habitats around the world and can now be found in most northern states.
The one saving grace for turtles is that people identify with them. I was picking up a rental car recently and when I mentioned the Field Station, the rental agent enthusiastically started detailing his many valiant efforts to protect nesting turtles on his property down on the Cape. If you see a turtle trying to cross a road on island, it is possible to help them across. First and foremost, do not risk getting hurt or causing harm to others by unsafely pulling off the road or trying to dodge traffic. However, if the opportunity to safely move a turtle occurs, move it in the direction it was heading and off the edge of the road. It is trying to get to habitats and resources it needs. Do not take turtles home or move them to a “better location.” And keep your eyes open and slow down at the island’s several turtle crossing locations, many of which are marked by cute signs.
Portions of this article were previously published in 2009 and 2010 and can be read at nantucketconservation.org/page.php?section=2&page=current_research and www.yesterdaysisland.com/2010/science/21.php. An excellent turtle blog with lots of science and pictures can be found at http://borbl426-526.blogspot.com/2012_01_01_archive.html.