It’s an exciting and surprising discovery for those who didn’t know they had been working, or more likely sleeping, for years with the endangered bats flying overhead.

“They’re out there, we’re just not seeing them,” nature resource specialist James Bruch said Wednesday.

The Kaho’olawe Island Reserve Commission confirmed the presence of the ‘ope’ape’a, which gained endangered species status in 1970, by placing eight detectors across the island in April 2016. The detectors record bat sounds using high-frequency ultrasonic microphones with a range that exceeds the human hearing limits of 20 kilohertz. Most bat detections were above 25 kHz.

“They can make noises that are in the level of human hearing, but most of them are higher than that,” Bruch said. “They’re basically echolocating — much like dolphins — locating insect prey. When it bounces off an insect, it’ll come back to them and it’s a way to see in the dark. It tells them there’s an insect or food resource.”

Bat detectors featuring high-frequency ultrasonic microphones listen for bat sounds beyond the human range of hearing. -- Kaho‘olawe Island Reserve Commission photo

The first bat was detected in June 2016, but none were recorded thereafter until August, Bruch said. Detections peaked in September and October, but went down again in December and January. Detections stopped in February and March, though April had a couple detections.

The study found that bats only visit seasonally, and during peak months a bat would be detected one in every four nights. All of the detectors recorded bats in habitats across the island.

The U.S. Fish and Wildlife website says that the hoary bat, with a heavy dark fur coat, has been seen on Maui, Hawaii, Molokai and Oahu but only may live on the Big Island, Maui and Kauai. Population estimates have ranged from hundreds to a few thousand, though those estimates are based on limited and incomplete data.

Bruch, who has been working for KIRC for the past 15 years, said he has never seen a bat on the island, but knows many workers and visitors have reported sightings over the years.

“Every once in a while either a worker or volunteer would say, ‘Oh, I think I saw a bat,’ but no one could verify it,” Bruch said. “We’ve put out a detector one or two nights out of the year and nothing was ever picked up.”

Difficulties in seeing Hawaii’s state land mammal may be due to its small size and dark color. Females, which are larger than males, have a wingspan of about a foot, weigh about half an ounce and are dark brown and black.

Their active times also are at night with 86 percent of detections occurring between 8 p.m. and midnight. The peak time was 10 p.m.

Bruch said detectors at the commission’s base camp picked up bats without workers or volunteers even knowing they were overhead. He said many of them work hard during the day and fall asleep without seeing or hearing the bat.

“It makes you really think,” he said. “Knowing they’ve been there the entire time is pretty amazing.”

“That’s the neat part about it that they’re there right over where people camp,” Bruch added. “It adds a whole other element of interest to Kahoolawe that there’s this rare native Hawaiian species flying around out there, and we had no idea. The more we look the more we find.”

Data of the detections suggest that the bat migrates to Kahoolawe and then returns home to Maui, and possibly Lanai, on a nightly basis, Bruch said. He said a small resident population also is possible and the bat may be using the island for breeding.

Bruch sees no reason why the island cannot be a sanctuary for the bat, which fits into the overall mission and vision of KIRC. The bat survey was a collaboration with U.S. Geological Survey, Island Conservation, Maui Nui Seabird Recovery Project and Starr Environmental as part of the Kaho’olawe ‘Ope’ape’a Working Group.

“If their threats are minimized, I don’t see why not,” Bruch said of the bats making Kahoolawe their home. “In ancient times, it could sustain a bat population pretty easily over there when the entire island was native Hawaiian dryland forest and shrub land.”

The commission has been working diligently to eliminate invasive species and predators to make the island sustainable for native plant life, insects and animals, such as seabirds and bats.

It still is unknown how many bats visit the island, what sort of habitat could sustain a local population and how Maui’s wind farms are affecting migration to Kahoolawe.

The bat detectors were on loan from USGS on the Big Island and the commission had to return them, Bruch said. He said the commission is actively reviewing the bat data and is hoping for additional funding for more research.

“It’s amazing how little we know about the species,” he said. “They’re cryptic. They’re harder to detect, but the technology is much better and the prices are coming down to where it’s more reasonable to do studies like this.”

* Chris Sugidono can be reached at csugidono@mauinews.com.