Along a rushing river in Minnesota's north woods, Maria Berkeland and I are slogging through stagnant oxbows, combing the river banks, and fighting our way through thick brush as we search for a rare reptile, the wood turtle. It is a sunny day in early June, and turtles should be out basking in the warm sun. But wood turtles are well camouflaged against the dark, mucky soil, and they like to tuck into thickets of dead grass and under downed trees, so we must walk slowly, constantly scanning the ground.
The wood turtle (Glyptemys insculpta) is a medium-sized turtle, likely unfamiliar to most Minnesotans. Its shell is brown with yellow markings and has an intricate pattern of circular grooves that form what look like irregular pyramids. The underside of the shell is a golden yellow with large black blotches. The colors are especially vivid and beautiful when the shell is wet. The pattern of underside blotches is unique on each turtle, allowing individual turtles to be identified from just a photograph. Wood turtles look almost as if they are smiling at you.
Wood turtles occupy a range that includes the Upper Midwest, the northeastern United States, and parts of eastern Canada. They are found only in a small number of places in southeastern and northeastern Minnesota. They prefer fast-moving rivers and streams with a sand or gravel bottom and bordered by deciduous and coniferous forests. In spring, wood turtles spend much of their time in or close to the river, nesting in openings such as sand points, sandbars, and cut banks along the river's edge. In the summer and early fall they spend most of their time on land searching for berries, leaves, mushrooms, insects, and earthworms to eat.
On this early summer day we are sticking close to the river, hoping to find wood turtles and learn more about them so we can help their kind.
A Vulnerable Species.
The wood turtle is a threatened species in Minnesota. It is the most terrestrial of the state's riverine turtle species, and it faces hazards in its travels between hibernation sites in the river and nesting and foraging sites on land. Among the many threats facing wood turtles are road mortality, nest flooding, predation, habitat fragmentation and destruction, invasive species, and poaching. The cumulative result of these threats is a species that is declining across most of its range and is being considered for protection under the federal Endangered Species Act.
The Minnesota DNR's Nongame Wildlife Program is studying wood turtles to figure out how we can help this vulnerable species. The project is funded by citizen donations to the Nongame Wildlife Program and a grant from the U.S. Fish and Wildlife Service. It is a collaborative effort with the University of Minnesota Duluth's Natural Resources Research Institute, West Virginia University, the U.S. Forest Service, and the Fond du Lac Band of Lake Superior Chippewa. Maya Hamady, now retired from the Nongame Wildlife Program, initiated the project with partners from Wisconsin, Michigan, and Iowa so the four states could combine efforts and collectively identify ways to help wood turtles in the region.
Along the river bank, Maria spies a wood turtle and grabs it before it can slide back into the safety of the river. Maria, a graduate student at the University of Minnesota, is among the researchers who have spent the past four years searching for wood turtles along northeastern Minnesota rivers. The turtle flails its chunky legs trying to escape from Maria's grasp. Having no luck, it tucks tightly into its shell.
It turns out the creature has been through this before. Maria counts the notches that researchers previously engraved into the edge of its shell. Turtle number 3318. This turtle was last captured in 2012 along this stretch of river. Maria measures, weighs, and photographs the turtle, then turns it over to determine its age.
The bottom of the shell has growth lines that resemble growth rings on a tree. And indeed, they can be used the same way. Maria counts each growth line to estimate how old the turtle is. When a turtle reaches 20 to 25 years of age, the lines begin growing close together, and they wear away after years of sliding over sand and rocks. The growth lines are becoming too difficult to count on this turtle, but it was 20 when it was last captured in 2012, making it 26 years old now. The oldest wood turtle documented in Minnesota was at least 55 years old when it was captured in 2014.
Maria releases turtle 3318, and it quickly slips into the river. The University of Minnesota will use the information from this turtle to assess how the population is doing. Ron Moen, head of the Natural Resources Research Institute lab studying wood turtles, says, "With over 1,000 turtles marked since 1990, we can reconstruct the population over the past 30 years. The model shows that adult survival needs to be very high to maintain a stable population."
Few wood turtles make it to adulthood. But those that do typically have long life spans and go on to replenish the population, albeit slowly, for many decades. Even a small increase in adult mortality can cause the population to slowly decline over time.
Turtle Survival Techniques.
It can be tough out there for wood turtles. When they cross roads or trails, the slow reptiles are no match for fast-moving vehicles that can kill or injure them. Predators such as raccoons and foxes are an ongoing threat. Flooding can destroy their nests and reduce their reproductive success for a season.
Turtle road mortality is related to habitat destruction and loss of habitat connectivity, which alone are major threats to wood turtles. Increasingly, development, agriculture, and roads are fragmenting the areas these turtles call home. This puts turtles at risk. They often cross roads to get to nesting and foraging habitats—a difficult task for slow-moving turtles, especially when your strategy is to tuck into your shell and stay in place when frightened.
Wood turtles nest in sandy or gravelly areas, and they are attracted to sand mines, gravel pits, agricultural fields, and roads when these places are conveniently located near the river or if natural nesting sites are lacking. But this can be a risky gamble, resulting in high nest failure and female turtles killed while crossing roads. Adult females are particularly susceptible to being killed by vehicles as they travel to seek out a nesting site, and loss of breeding females can be detrimental to population sustainability.
Accordingly, the Nongame Wildlife Program, with additional funding from the Minnesota Herpetological Society, is experimenting with ways to help wood turtles: putting up fencing to keep them off roads, creating flood-safe nesting habitat, and installing barriers to protect nests from predators. Fencing was installed in locations where turtles were at risk of being killed. Nesting habitat was created nearby as an alternative to the road. At each created nesting site, vegetation was removed and the soil loosened to create open areas for nesting. These created nesting sites are strategically located in areas with good foraging habitat, near the river, and accessible to turtles without crossing roads, increasing habitat connectivity. However, keeping turtles off roads has been a challenge, and we are still experimenting with different fence material and design.
The Natural Resources Research Institute is using field surveys, trail cameras, and telemetry to determine if these techniques are successful at reducing the number of turtles that are killed and increasing the number of eggs that hatch. It's also establishing long-term monitoring sites because the real measure of success will be if these techniques help sustain or even increase the population over the long term.
Catch and Release Science.
Maria and I visit one of the created nesting sites and nearby fences. We walk past the fencing, wade through a small alder wetland, and climb an embankment to a mound of sand and gravel next to the river. Searching the grasses around the site, we find three female turtles basking in the sun. Picking one up, Maria gently extends its hind leg so she can press her finger inside the shell and along the body cavity. She feels eggs, about the size of small gumballs. The turtle still has a couple of weeks until she is ready to lay them.
We know this turtle has not been captured before because it has no notches on its shell. Maria gets out an electric file and notches the side of the shell in a pattern that is unique to this turtle, allowing researchers to identify it when it is caught again. The outer layer of the shell is made of keratin, the same substance as fingernails, so this does not hurt the turtle. When we are done measuring and photographing her, we let the turtle go and hope she will lay her eggs on this site in a couple of weeks.
If she does, the odds are not good that they will hatch. The Natural Resources Research Institute is finding that the vast majority of wood turtle nests are being destroyed by predators, often within hours of eggs being laid. Using motion-sensor cameras, scientists have found the main culprit is badgers. Raccoons, ravens, and skunks are also guilty. To help reduce predation, the university has put metal cages over some nests, but badgers still managed to dig up nests. We installed an electric fence on one of the created nesting sites to see if this was more effective. So far it has been. No predators have made their way through the electric fence, and the site is producing hatchlings every year. Some hatchlings are given a microchip that will let us identify these turtles if they make it to adulthood.
Nest flooding can be related to human-caused changes on the landscape. For wood turtles to thrive, they need both healthy river systems and healthy terrestrial habitats. Our northern forests have changed significantly since Euro-American settlement. Many forests once dominated by pines have been converted to aspen. In addition, lack of fire and introduction of invasive species, like earthworms, have changed the ground layer where turtles forage. Other land-use changes such as increased urbanization, agriculture, and roads have decreased and fragmented habitat. All of these changes in how we use the land also affect rivers. Under natural conditions, large rainfall events occur periodically, causing large flows of water to enter the river and spill out over the riverbanks into the floodplains. These pulses of water are important for maintaining turtle nesting habitat; they scour away vegetation and deposit sand, creating open sandy areas for nesting.
When too much of the land around the river is developed or otherwise disturbed, river dynamics are affected. The amount of water running into the river increases and water quality decreases. The riverbed and banks can erode, and the banks can become steep enough to disconnect the river from the floodplain. The energy of the floodwaters becomes concentrated within the river's banks, causing sand points and sandbars to wash away in frequent floods. Wood turtle nests are more likely to become flooded and fail. Climate change, an emerging threat for wood turtles and many other Minnesota creatures, is already causing more flooding in Minnesota rivers.
An uncertain threat for wood turtles is poaching. Although it is illegal to take wood turtles from the wild, they are highly sought by the pet trade in the United States and abroad. People have been caught illegally capturing and selling wood turtles in other states, contributing to population declines in some areas.
Though these threats are significant, the Nongame Wildlife Program is actively working with partners and the public to address these risks. People who recreate outdoors or live in eastern Minnesota can help wood turtles by keeping a watchful eye for poachers and by using sandy areas along rivers lightly, leaving no trace behind. Bonfires, camping, picnicking, and off-road vehicles can harm nests, and garbage left behind can attract predators. Wild turtles should not be brought home as pets, and pet turtles should not be released into the wild.
A Plan for Protection.
Because of all the perils that wood turtles face, the Nongame Wildlife Program and our partners are developing a conservation plan for the species in Minnesota that will identify project priorities and set conservation goals. The plan will identify monitoring, research, and management projects needed to sustain wood turtle populations in the state.
After a successful day on the river, with nine turtles caught, Maria and I head back to our truck. Piling our field gear in, we hope that the turtles we caught today will be able to overcome the numerous threats that lay ahead. With a little luck, we will see them—and their grinning faces—again as we capture them on future surveys.
The Nongame Wildlife Program is primarily funded by citizen donations, making projects like this possible. See mndnr.gov/nongame for information on how to donate.
To see a video of wood turtle researchers in action, visit the Minnesota Nongame Wildlife Program on Facebook.