Research provides new information about turtle species
Assistant Professor of Biology Joshua Otten’s research findings about northern map turtles were recently published in two scholarly journals.
Bigger is better
The first, “Bigger is Better: Age Class-Specific Survival Rates in Long-Lived Turtles Increase With Size,” published in January of 2024, involved capturing 1,726 turtles over three years in Michigan’s Kalamazoo River. Otten used mark-recapture methods to determine survival rates for turtles of all ages to understand population stability.
“There hasn’t been a study like this,” Otten said. “Before, biologists would evaluate egg survival, because the eggs are easy to count how many hatched, or the adults. There was missing data on the age class of zero to 2-year-old turtles, but because we were able to capture so many turtles, including younger individuals, this study fills in this knowledge gap.”
Otten confirmed the hypothesis that as the turtles grew larger, they had a higher annual survival rate. The data is helpful for habitat management practices, especially because the results indicated that this common turtle species is undergoing a population decline that will continue if there are no management interventions.
“I really think it was interesting to see that the 1- to 2-year-old turtles survived better than what I originally thought,” Otten said. “It was about a 40% annual survival rate, which is still much lower than adults, which have 90-95% annual survival. Knowing that those young turtles have a higher chance of survival provides important data for long-term conservation practices. If a turtle can at least hatch out of the egg and into where it would live as an adult–it has a pretty decent chance of surviving.”
Otten said spending funds to protect turtle nests, or reducing predators that eat turtle eggs, would increase the likelihood that hatchlings will make it to adulthood.
Sun Basking
In Otten’s research, “Here Comes the Sun: Thermoregulatory Behavior in Ectotherms Illuminated by Light-Level Geolocators,” published in April of 2024, a team of researchers proves the functionality and usefulness of a new form of data collection to quantify the behavior of wild turtles.
They used commercially available, multi-purpose light-level geolocator dataloggers to continuously record light environment and time spent out of water for five months in the life of northern map turtles in the Kalamazoo River. Otten says this is the first time biologists have been able to collect minute-by-minute data on what the turtle is doing all day. Researchers put radio transmitters and dataloggers on male and female turtles, tracking them down the following year to download the data onto a computer.
Otten and his team learned a lot from the dataloggers. They already knew that turtles need to bask in the sun because they can’t regulate their own temperature like humans, but they knew little about the basking behaviors of the turtles.
“The big thing we found was in the springtime, the turtles are more exposed and bask a lot more,” Otten said. “As the water and air warm up, the turtles don’t have to be out of the water as much to hit their optimal temperature. So the amount of time they are basking decreases by about August and then you see a bit of a spike again before they go into hibernation in October.”
Otten plans to continue studying the data he has collected to learn more about the hibernation of additional turtle species and why they sometimes come out of hibernation in the middle of winter. He also says collecting data over time can explain how climate change is impacting turtle populations.
“Turtles need the sunlight to metabolize their food and if they’re getting too hot, they are going to be hidden more often and not be as active,” Otten said. “This might slow growth rate, it might slow how long it takes for an individual to reach sexual maturity. The earth warming slightly each year potentially alters their behavior quite a bit from one year to the next.”
This summer, for his next round of research, Otten, and his Cornell Summer Research Institute students plan to continue using dataloggers to record the temperature and behavior of ornate box turtles in Iowa. They will evaluate potential anthropogenic impacts, such as climate change, on population demographics, movement patterns, and nesting behavior. Ornate box turtles are temperature-dependent sex-determined species, meaning that the temperature at which eggs are incubated influences the sex of the hatchling.
“If a nest is incubated two degrees warmer than the pivotal temperature then a nest might produce all females, and two degrees cooler, all males,” he said.
Why this research is important
Turtles play an important role in our ecosystems but are losing much of their habitat to farms and cities. They eat a variety of small plants, insects, and animals, including dead biomass, which cycles important nutrients for the health of our ecosystem. Turtles are often considered the cleaning crew, removing harmful bacteria from the land and water where they live. Turles also carry seeds to replenish and restore the land and water.
Understanding turtle activity, development, and population growth can provide more insight into the management of their habitats and conservation practices people can observe to keep the ecosystem we all live in healthy.
