Going batty

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Hawaii’s newest state symbol also is one of its least understood.


Hawaii’s newest state symbol also is one of its least understood.

The ‘ope‘ape‘a, or Hawaiian hoary bat, officially was named state land mammal last week in a bill signed by Gov. David Ige.

Though the bill was four years in the making, the bat was a shoo-in for the eventual title: It’s the only land mammal endemic to Hawaii.

Researchers on Hawaii Island hope the designation will lead to more interest in the elusive animal, which was put on the federal endangered species list in 1970.

“I think it’s fantastic for the people and the state to become more aware,” said Frank Bonnacorso, a research wildlife biologist with the U.S. Geological Survey. Bonnacorso works out of the Kilauea field station at Hawaii Volcanoes National Park and has studied Hawaiian hoary bats for 11 years.

Much of what is known about the ‘ope‘ape‘a comes from work produced by the University of Hawaii Cooperative Studies Unit, a collaboration between the University of Hawaii at Hilo and the USGS Pacific Island Ecosystems Research Center.

“We’re still trying to figure out their status statewide,” said John Vetter, wildlife biologist with the state Department of Land and Natural Resources.

Breeding bat populations have been documented on Kauai, Maui and Oahu, Vetter said, but “the Big Island is where we have the best information.” Most of that only recently was gleaned.

“Until 15 to 20 years ago, we knew almost nothing,” Vetter said.

The bats don’t make it easy on researchers. Solitary by nature, they roost in the shade of tall treetops during the day. And they are tiny: Females, the larger of the two sexes, typically weigh just 18 grams.

“The only time people get direct visual contact with these animals is maybe a small period of twilight around sunset and sunrise,” Bonnacorso said.

Because the ‘ope‘ape‘a is solitary, it’s nearly impossible to get an accurate population count. Bat species that roost in colonies can be counted en masse as they leave their homes to hunt at night, but figuring out a count based on individuals is a different matter.

“I wish I could; I can’t begin to guess,” Bonnacorso said. “Lots of agencies would like to know that. There’s no scientific way to come up with a population, so we’re dealing with individuals and trends that we see in individuals.”

Researchers place tiny radio transmitters on bats to detect migration patterns and go out at night to record echolocating bats as they hunt for prey. Those methods can give a sense of where a certain bat is traveling, but they can’t account for an entire population.

“It’s a bit like studying a snow leopard — low abundance and widely dispersed,” said Marcos Gorresen, a biologist at the cooperative studies unit.

But the radio transmitters and acoustic readings do help give a sense for the bat’s habitat. It’s found just about everywhere on the Big Island, from sea level to the mountain summits, moving into the warmer lowlands in the summer when pups are born.

Acoustic readings are most frequent and consistent at Laupahoehoe Natural Area Reserve, Gorresen said, and distribution trends are fairly stable.

“They’re very wide-ranging for such a small animal,” he said. He’s measured one-way flights of more than 9 miles as the bats go out to forage.

The ‘ope‘ape‘a’s greatest strength might be its versatility. It’s an opportunist, not only in terms of habitat but also diet.

Christopher Todd began studying the bat’s eating habits as a UH graduate student. Like so many other aspects relating to the bat, diet hadn’t been fully analyzed before.

Todd found that the bat eats at least five different species of beetles, most of which are invasive. It also feeds on moths, and has been seen gathering at cave mouths specifically to forage on the moths as they leave.

“You’re constantly finding out things that were not known,” Todd said. “They’re pretty amazing.”

Gorresen is struck by the tiny animal’s overseas migration from North America to Hawaii.

“They made it across thousands of kilometers of open ocean,” he said. Another species of bat appears in the fossil record here, but that animal lived only in the Pleistocene era.

“They really are remarkable evolution(ary) creatures,” Todd said.

The best place for the casual bat fan to catch a glimpse of the ‘ope‘ape‘a is at Hilo High School’s track, when the lights are on. Moths are attracted to the lights, and bats in turn come out for the easy prey.


“Watch up, and watch the moths — you’ll see them,” Bonnacorso said.

Email Ivy Ashe at iashe@hawaiitribune-herald.com.

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