Gaea Crozier of the MN DNR is a nongame wildlife biologist out of Grand Rapids who works with wood turtles (Glyptemys insculpta) and other creatures. She spoke for the MHS General Meeting on April 1st about the results of a recently completed project on wood turtles in northeastern Minnesota through MN DNR’s Nongame Wildlife Program. The project examined threats to the turtles and the effectiveness of management aimed at addressing those threats. Crozier also spoke about current efforts related to wood turtles in northeastern Minnesota.
Wood turtles are a threatened species in Minnesota, ranging over the eastern portion of the state. They typically overwinter in streams and emerge in the spring. They become terrestrial after nesting, but generally remain within 100 meters of flowing water (when not nesting).
Threats to wood turtles are numerous, including habitat loss and fragmentation, road mortality, predation, nest flooding, altered river hydrology, illegal collection, forest management and agriculture, contaminants, and climate change.
With limited time and resources, the DNR needed to come up with a Wood Turtle Conversation Plan to identify where to focus their efforts. (It’s on the DNR website at https://files.dnr.state.mn.us/eco/nongame/projects/mn-wood-turtle-conservation-plan. ) This plan will be driving their work for the next 10 years.
The project Crozier presented had been a collaboration between the DNRs of Iowa, Michigan, Minnesota and Wisconsin, with help from additional partners. Ron Moen at the University of MN supervised three graduate students who did most of the work (with grant funding). They are grateful for the assistance of the MHS in contributing to the grant funding.
There were four main goals for the wood turtle project: reduce adult mortality, increase nest success, conduct surveys and monitoring, and perform research to learn more about the turtles.
Four temporary road barriers were installed to reduce the number of turtles on roads. This did reduce mortality but did not keep all turtles off the road. The barriers would be truncated at driveways etc. and It was easy for people to tear them down. Turtles also walked to the end of the barriers and went around them.
Fortunately, they didn’t see a lot of mortality, but there were a few hot spots where there was higher turtle mortality. They plan to monitor 20 sites to see how prevalent this is.
They found a surprisingly large number of 71 dead turtles along one stretch of river during the project. They were not sure what caused that mortality event. There was a large decrease in turtles along that stretch of the river. They are doing surveys to see if it’s still going on. They are also conducting disease testing in live turtles to see if illness has had an impact. A similar incident hasn’t happened since.
To increase nest success, they worked on creating better nesting habitat. They restored or created 23 flood-safe nesting sites near the road barriers as an alternative to nesting on the road. During field surveys they learned that they have been able to increase the number of turtles using restored existing sites. (In one area, the number increased from 5 to around 25).
But newly created nesting sites were not used at all, possibly because they had been placed inland from the river quite a ways due to expectations that rivers will be flooding more in the future. New nesting sites also used more dirt than sand, and vegetation grew in quickly.
The Wisconsin DNR had 50% of their created nest sites used by turtles, but they were placed right off the river and used more sand.
The project monitored nests using field surveys and game cameras. They found that only 5% of nests hatched. Badgers were the main predators (85%) but raccoons, red fox, skunks and ravens also raided nests. Predator presence was high during nesting season but low during the hatching period.
Individual nest cages and electric fences were used to protect nests. The nest cages took a lot of labor. The electric fences could be put in place and maintained more easily. Protected nests had a 50% success rate compared to 5% for unprotected nests. They produced 174 hatchlings from protected nests during phase 1 of the project. They’re going to try nest boxes during the next phase.
A long-term monitoring program has been established, surveying 16 sites. The protocol is to walk 8 parallel transects along the river for 500 m at each site, 6 times during the spring. They use the mark-recapture method to collect data on abundance, sex ratio, age class structure and survivorship.
They plan to monitor sites every 5 years to get an idea of population trends. They collected baseline data in Phase One.
Doing surveys helps them to better understand where turtles are found and where nesting sites are located, so they can identify where to focus conservation efforts in the future.
As part of their research, they have collected telemetry data on 22 female and 6 male turtles for 1-3 seasons. They are analyzing the data to determine preferred habitat types and movement patterns and will use this information to update their wood turtle management guidelines.
Turtles show strong site fidelity to nesting, foraging and hibernacula sites. The average home range size was 544 acres for females and 146 acres for males. Maximum movement along the river corridor was 5.4 miles. Females moved 128 m/day during nesting season (further than expected) and males moved 48m/day consistently across seasons.
They have created a population model based on 30 years of mark-recapture data. The model shows that a 95% survival rate for adults is required to maintain the population. That’s very high.
Increasing egg/hatchling survival is the best strategy for increasing the population, assuming the adult population remains high. There is a lack of data on hatchling survival, and that is needed.
Modeling suggests the population has been fairly stable over the past 30 years—but the growth rate has declined over the last 15 years. That is concerning.
Review submitted by Renee Valois, MHS Recording Secretary; Edited for website by Laura Windels