Keeping Nesting Map Turtles Safe on the Juniata River

In addition to the many Pennsylvania wildlife crossings developed to help animals safely traverse highways and roads, a project in Huntingdon County is keeping threatened species off our roads entirely.

A regional hotspot for a vulnerable species

Huntingdon County, Pennsylvania is a hotspot of turtle diversity. Sitting at the interface of northern and southern species’ ranges, it also is home to vast expanses of undeveloped land. In fact, 78% of the county remains wild[1], and the region is home to large tracts of public lands including Rothrock State Forest, state game lands, and Raystown Lake, the largest lake that’s entirely within Pennsylvania’s borders[2]. Many other wetlands, including the Juniata River and its tributaries, provide ideal habitat for a variety of turtle species, including the northern map turtle[3].

The northern map turtle inhabits large streams and rivers with high water quality, and like many turtle species, has declined across much of its range in North America. Northern map turtles require open tree canopy near rivers for nesting, yet as roads and waterfront development overtakes this habitat, the turtle has been driven out of much of their historic range. For this reason, measures to protect remaining habitat (such as the Raystown Branch of the Juniata River) and to prevent road mortality in these remaining areas, are increasingly critical for this native Pennsylvania turtle species.

Beyond its need for a specific type of river bank habitat that is increasingly rare, two other factors increase the vulnerability of the northern map turtle.

The second factor is the species’ long maturation periods. Female northern map turtles take at least a decade to mature before they are able to reproduce, then only laying eggs once or twice annually after they’ve reached sexual maturity[4].

Third, they have unusually high natal philopatry, meaning they return to where they were born to lay their eggs. This means that if the habitat where they themselves hatched has been destroyed, they are unlikely to move to a similar habitat elsewhere on their own. For these reasons, the northern map turtle populations are in decline and under threat, considered a species of “conservation concern” in Pennsylvania while being listed as endangered in Maryland[5].

A low-tech solution for protecting northern map turtles

In 1999, a new segment of U.S. Route 522 was completed near Mount Union, Pennsylvania, an hour south of State College in Huntingdon County. Located along the banks of the Juniata River, the road was built directly on top of the female map turtle’s historic–and critical–nesting grounds.

In 2000, the year after U.S. 522 was completed, over 50 females were killed crossing the new road when they moved onto land to lay their eggs during nesting season, which runs from May to early July in central Pennsylvania[6].

The blue line represents the location of the exclusion fence between 522 to the west and the Juniata River to the east.Photo by Roy Nagle | Used by permission

While any wildlife road deaths are a tragedy, the deaths of breeding females were particularly troubling. As with most threatened species, the population’s future rests on ensuring the breeding females can safely get to their nesting grounds, lay their eggs and reproduce. Local experts called on PennDOT to put a barricade in place to first keep the female northern map turtles from accessing this busy stretch of highway, emphasizing this was a critical step before any other habitat changes or improvements were made[7]. A simple 1 meter high, 1,150-meter-long chainlink fence was installed between the river and the new highway to prevent turtles from moving onto the road, and it was immediately effective.

The female turtles still instinctively came out of the river and climbed up the bank, but were stopped at the new barrier, initially nesting as high up the bank – and as close to their original sites – as possible[8]. Road deaths immediately began to drop – 10 in 2000, 3 in 2001 and 1 in 2000. In 2024, there had been no map turtle road deaths in the previous two years along the U.S. 522 bypass[9].

The fence keeping nesting map turtles from U.S. 522.Photo by Roy Nagle | Used by permission

Benefits for researchers

The crisis of northern map turtle road deaths at Mount Union was averted, but the nesting ground was now constricted – the females were safe, but crowded. This provided an opportunity to study how to best enhance nesting substrate in this newly contained environment. To that end, conservationists are working to better maximize breeding habitat in the region for the discerning map turtle, experimenting with combinations of sand, shale and the widely available coal waste in the region to understand turtle preferences[10].

The challenges of turtle conservation at Mount Union provided opportunities to compare different strategies and methods of protecting adults, providing habitat, and ensuring incubation of thousands of turtle eggs. Over two decades, researchers marked and released more than 1,200 hatchling turtles into the Juniata River and documented important aspects of the nesting ecology and habitat use of adult females. The strategies developed at Mount Union were implemented later at other habitats in Huntingdon County, in research partnerships with conservation agencies.

As monitoring has continued at these sites, the results have made the importance of protecting the nesting northern map turtle females even more apparent. Monitoring of juvenile turtles has found that more than 50% of the returning females at the Mount Union site are the descendants of just a few “supermoms” – indicating that some individual females are especially critical to population survival[11].

A cautionary tale

While in this instance, mitigation measures were effective in eventually protecting the target species after significant initial losses, it’s also a reminder of the impact that projects like highway expansions have on the habitats they fragment – or eliminate entirely. The initial deaths and the rush to find a solution could have been avoided by taking critical habitat into account when siting the project.

References

1. PA Department of Environmental Protection, Countywide Action Plan Snapshot: Huntingdon County, Pennsylvania.
Phase 3 WIP County Snapshots, 2020.

2. Baltimore District, Army Corps of Engineers, Raystown
Lake – Natural Resource Management, accessed at: https://www.nab.usace.army.mil/Missions/Dams-Recreation/Raystown-Lake/Natural-Resources/ 20 February 2025.

3. Western Pennsylvania Conservancy, Juniata Forward:
Building on 25 Years of Conservation (draft), September 2024, accessed at: https://waterlandlife.org/wp-content/uploads/2024/09/Juniata-Forward-Full-Plan_DRAFT-2024.pdf 20 February 2025.

4. Roy D, Nagle and Justin D. Congdon, “Reproductive
ecology of Graptemys geographica of the Juniata River in central Pennsylvania, with recommendations for conservation,” Herpetol. Conserv. Biol., 11(1):232-243, April 2016.

5. Roy D Nagle and Travis J. Russell, “Nest Site Fidelity of
Northern Map Turtles, Graptemys geographica,” Chelonian Conserv. Biol., 19(2), doi:10.2744/CCB-1439.1 December 2020.

6. Ibid.

7. Roy D Nagle, Research Ecologist, University of
Michigan, personal communication, 16 August 2024.

8. Roy D Nagle and Travis J. Russell, “Nest Site Fidelity of
Northern Map Turtles, Graptemys geographica,” Chelonian Conserv. Biol., 19(2), doi:10.2744/CCB-1439.1 December 2020.

9. Roy D Nagle, Research Ecologist, University of Michigan, personal communication, 16 August 2024.

10. Ibid.

11. Roy D Nagle and Travis J. Russell, “Nest Site Fidelity of
Northern Map Turtles, Graptemys geographica,” Chelonian Conserv. Biol., 19(2), doi:10.2744/CCB-1439.1 December 2020.