Hibernating Bats at Tippy Hydro at Highest Number to Date

The Indiana bat is one of the species identified in the Tippy Hydro spillway.

A group of bats at our Tippy Hydro on the Manistee River are hanging out for yet another winter. Clustered in large groups, approximately 24,000 bats of at least four different species are hibernating in the dam’s cavernous spillway this winter, making it the highest population counted to date.

Dr. Allen Kurta, professor of biology at Eastern Michigan University and bat expert has been monitoring the population for the past 18 years. He and his team of students check for size of the population, disease and presence of endangered species. White-nose syndrome, a new fungal infection that can be deadly for bats, was not found on any of the bats.

“The population of bats at Tippy appears healthy,” Dr. Kurta said.

The group includes at least one female Indiana bat, an endangered species. Dr. Kurta noted that thanks to a numbered band on the bat, he knows that she was first seen in the spillway in 2001, making her at least 11 years old. Dr. Kurta and his team also found and banded 10 eastern pipistrelles, a species of special concern in Michigan.

A small portion of the approximately 24,000 bats which hibernated in Tippy dam’s cavernous spillway this winter.

Tippy Hydro, completed in 1918, has been a winter home for bats for as long as employees can remember. With temperatures a few degrees above freezing and moist walls, the spillway is similar to a natural cave and acts as a hibernaculum, or a place where bats hibernate. It is the largest hibernaculum in the Lower Peninsula and second in the state only to the copper mines in the Upper Peninsula.

“It’s a bit of an educational factor to those who don’t work at Tippy,” Lorren Hannahs, Manistee River hydro supervisor, said. “They don’t always get it, but we like how unique it is because of the bats.”

To protect the bats, strict regulations are in place regarding operations at the dam. Employees are only allowed to do maintenance work that would require using the spillway between June 1 and Sept. 1. There also are regulations on when timber can be cut within the boundaries because the bats raise their young under loose tree bark of dead trees during the summer months.

In the past, Dr. Kurta has tied glow bands to the bats to track hunting territory and to determine what types of trees are used most frequently.

Hannahs said school groups come in every year and they spend a lot of time focusing on educating students about the bats.

“We have posters up that explain things,” Hannahs said, “like the reason bats hang upside down is because their bone structure is light framed and therefore too weak to support their weight.”

Bats help the environment by controlling insect populations, pollinating plants and dispersing seeds. With a lifespan of approximately 10-20 years and a pattern of returning to the same hibernaculums, it’s safe to assume the bats at Tippy Hydro will continue to thrill visitors and serve as a symbol of the importance of conservation.

By: Sarah Hood