Moles are digging, Woolly Bears are emerging and preparing to pupate and develop into Isabella Tiger Moths, and Painted Turtles are emerging and warming their cool bodies by basking in the sun. Red-winged Blackbirds, Killdeer and Wood Ducks are back. Silver Maple buds are beginning to swell. Ticks are out and about. New signs of spring are appearing on a daily basis, and those of us who keep nature journals are busy recording our discoveries. These events may happen every year, but they never get old.
Studies based on the records that Henry David Thoreau and other naturalists kept for Concord, MA in the middle of the 19th century have found that the flowering of plants, leaf-out, butterfly emergence and the arrivals of some migratory birds are occurring earlier now than they did 165 years ago — anywhere from a day to three weeks earlier depending on the species — driven mostly by warmer spring temperatures. Since the mid-1800’s Concord has lost roughly a quarter of its wildflowers while an additional third have become rare.
Whether it be through a written journal, sketches, photographs, videos or taped voice recordings, the observations we make today are a valuable resource for phenology (the timing of biological events) and climate change studies and for our own personal histories of natural places we visit year after year. We are so fortunate that the current state of the world doesn’t prevent our appreciation of and participation in this annual spring ritual.
Water temperature of fifty-nine degrees Fahrenheit is the magic number for Painted Turtles in the fall. Below it, their metabolism slows to a near standstill – their heartbeat slows to only one beat every few minutes and they do not breathe through their lungs (if conditions allow, they may absorb oxygen dissolved in the water through specialized skin cells near the tail). Their body temperature averages 43°F. when hibernating in the mud at the bottom of ponds. Occasionally a Painted Turtle is seen swimming under the ice, but for the most part, hibernation rules from October to April in northern New England.
When the water reaches 59°F.- 64°F. in the spring, Painted Turtles become active again. In addition to foraging, they immediately start basking in the sun. Being cold-blooded, or ectothermic, they need this external source of heat to warm their body, but the UV light also regulates their metabolism and breeding as well as helps produce Vitamin D3, which is essential for the health of their bones as well as their internal organs.
Basking can also help relieve aquatic turtles of ectoparasites. Leeches are a blood-sucking ectoparasite that can cause anemia in reptiles. Drying out in the sun causes the leeches to shrivel up and die. Algae on basking aquatic turtles can also dry out and fall off, allowing the shells to retain their aerodynamic nature.
When a Painted Turtle crawls out of the roughly 39° F. degree mud at the bottom of a pond in early spring, it immediately heads to the nearest log or rock to bask and raise its body temperature. Turtles are ectothermic (cold-blooded) and must rely on external sources for the regulation of their body temperature. Thermoregulation is achieved both physically and behaviorally. A dark carapace (top shell) absorbs the sun’s heat, warming up the turtle’s internal temperature and the turtle regulates its temperature by shuffling in and out of the sun. It is imperative for the core body temperature of male Painted Turtles to reach 63° F., for only then can they start to produce sperm.
Naturally Curious is supported by donations. If you choose to contribute, you may go to https://naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.
Painted Turtle eggs hatch in late August or early September. The young turtles remain in their nest for varying amounts of time, often emerging soon after hatching but frequently not until the following spring in the northern part of their range. Once hatched and out of the nest, they head to ponds and rivers. Because they’re so small (roughly the size of a quarter) they are vulnerable to a wide variety of predators, including frogs, snakes, birds and fish.
Adult Painted Turtles leave their ponds in May, June and July to find a sandy spot in which to dig a hole and deposit their half dozen or so eggs. In most of their range, Painted Turtles hatch and emerge from their nest several months later, from August through early September. In the northern part of their range, however, the young turtles hatch in the fall but usually overwinter in their underground nest and emerge in the spring.
When turtles hatch, they use a modified scale called an egg-tooth, or carbuncle, located on the front of their upper jaw, to puncture their leathery egg shell. (Although referred to as an egg-tooth, it is not a real tooth.) Typically the egg tooth disappears in a matter of days or weeks after hatching. However, Painted Turtle hatchlings in northern New England retain their egg teeth through the winter, and emerge in the spring with it still intact, as this photograph demonstrates. (Thanks to Nancy and Rob Foote for photo op.)
Being an aquatic species, most painted turtles hibernate in the mud at the bottom of ponds. They dig down as far as ten feet where they spend the winter hovering around 43°. In the spring, when the temperature of the water approaches 60°, painted turtles begin actively foraging, but the first priority upon awakening is to warm up their bodies. Turtles are ectothermic, or cold-blooded, thus the temperature of their bodies is determined by the environment that surrounds them. To be active, painted turtles must maintain an internal temperature of 63°- 73°. They reach and maintain this temperature by basking in the sun, particularly in the cold, first weeks of spring. Once warmed up, the turtles will forage, and when they begin to cool off, basking resumes.
Competition for basking sites such as floating logs and rocks can be fierce. It is not unusual to see many painted turtles lined up on a floating log, or turtles piled one upon the other on a rock in an effort to maximize the effect of the sun’s rays. The heat they’re obtaining increases their metabolism, aids in digestion and allows males to start producing sperm. The sun also strengthens their shells and reduces the amount of algae on them, thereby reducing the chances of bacterial or fungal infection.