Manistee dam removal yields snake hibernaculum

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Snake Hibernaculum

A restoration specialist uses a video-scope to detect snakes. Image: Herpetological Resource and Management (HRM)

Conservation biologists have built the first artificial home for snakes in northern Michigan.

And they removed an entire dam to do it.

Experts say that the snakes need the help.

Native snakes, including the Eastern Massasauga rattlesnake and Northern water snake, require shelter from cold winters. But development threatens their habitat in what is “the greatest impact to amphibian and reptile populations and reproduction,” said David Mifsud, a wetland ecologist at Herpetological Resource and Management who helped with the restoration.

To meet their needs, some biologists create homes for snakes out of existing restoration projects. That’s what recently happened on the North Branch of the Manistee River near Kalkaska.

The Conservation Resource Alliance, a private conservation group that helps groups collaborate on restoration projects, restored nearly 150 miles of the river’s habitat. The project restored trout passage and the adjacent riverbank.

And biologists threw in an underground snake refuge as an unexpected bonus.

In 2008, the nonprofit group restored the 1,720-acre Flowing Well Trout Farm after it was bought by the state of Michigan. The former hatchery near Kalkaska was shut down after officials identified a whirling disease infestation in the trout it raised. The disease stems from a parasite that inflicts neurological damage in salmon and trout, causing their spines to harden. The fish can’t escape predators because they are forced to swim in a circular motion.

By 2013, the organization and its partners had removed a dozen 8-foot dams and five undersized culverts on the Upper Manistee River. That let fish swim through the newly connected floodplains. Until then, the Mecum Road crossing over the North Branch Manistee was considered the “worst remaining [stream] crossing on the North Branch of the Manistee,” said biologist Chris Pierce.

Dam removal and culvert construction left behind concrete on the site. Instead of hauling it away, restoration workers used it to restore snake habitat, Pierce said.

There was precedent for the move.

The U.S. Fish and Wildlife Service and the Natural Resources Conservation Service had done something similar in Wisconsin a couple years earlier. The restoration’s biologists copied that effort and made what is technically known as a snake hibernaculum.

Hibernacula are natural or synthetic structures used by dormant or hibernating species. They include existing burrows, caves, sinkholes, dikes and bridge foundations — anything that offers stable temperatures.

Snake Hibernaculum

HRM team member monitoring hibernacula for proper function. Image: Herpetological Resource and Management

When temperatures reach extremes, snakes seek refuge. As poikilotherms, snakes escape the cold by basking in the sunlight and the heat by burrowing underground.

Herpetological Resource and Management LLC, a Chelsea-based environmental firm, and Conservation Resource Alliance biologist Eric Ellis identified this opportunity for habitat improvement.

The conservation group built the hibernaculum following a snake model. It has already documented several species that use it, including the eastern hog-nosed snake. The environmental management firm continues to monitor the presence and distribution of reptiles, amphibians and aquatic macroinvertebrates.

An Eastern Hog-nosed snake after a recent meal (note the swollen body) observed while touring restoration sites Aug. 22 along the North Branch of the Manistee River east of Grayling, Mich. Part of the restoration of the former Flowing Well Trout Farm property involved a hibernaculum for snakes and other reptiles. Image:   Terry S. Heatlie

An Eastern Hog-nosed snake observed along the North Branch of the Manistee River. Image: Terry S. Heatlie

In summer 2011, a 14-foot pit was dug to keep the hibernaculum below the frost line so that it didn’t freeze in the winter. Workers then transported the excess concrete from the dam removal to the new site.

The move also made financial sense.

The hibernacula cost less than $2,000, but it would have cost “up to three times more to haul the concrete offsite,” said biologist Kim Balke, the Betsie River project manager for Conservation Resource Alliance. Balke recently oversaw the completion of a similar hibernacula in the Betsie River Watershed.

Large rocks and 3-foot concrete pieces were placed at the bottom of the pit to create natural voids where the snakes can hide. Smaller rubble and natural debris were layered over large concrete pieces to fill larger gaps. The structure was then concealed with a geotextile “filter” fabric and several feet of dirt, allowing for several points of entry.

Species inhabiting the North Branch of the Manistee are sensitive to environmental inputs such as pollutants and act as bioindicators — species used to monitor environmental health.

The Conservation Resource Alliance created the artificial hibernaculum to promote ecosystem growth and offset damage from development. The habitat adjacent to the Manistee provides a regional wildlife refuge buffered by thousands of acres of state-owned land.

Natural hibernacula created by other native species can be a “limiting resource,” Mifsud said. Design of these structures generally targets a specific species, but North Branch of the Manistee is the home to many species requiring safe living spaces. Critical microhabitats, like hibernacula, are often “unintentionally destroyed due to ignorance of what they are and their value to wildlife,” he said.

Removal of dams and the construction of microhabitats improve land degraded by mismanagement.

Support from the U.S. Fish and Wildlife Service and funding from existing partnerships allowed the Conservation Resource Alliance to complete the Flowing Well Dam Removal Project.

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