Radio Towers and Tiny Tags: Tracking Olympic's Bats Through the Winter

The new solar-powered Motus receiver at the Glines Canyon Spillway Overlook, above the Elwha River's former lakebed — good habitat for many kinds of bats. USGS photo / Hansen.

A winter mystery

September 2023. Three miles past the locked gate, beyond where floods washed out the road, stands the concrete spillway of the Glines Canyon Dam in Olympic National Park. The dam came out in 2014 in the Elwha River restoration, and the spillway now overlooks the old reservoir. Scientists are fixing a new instrument to it.

The question it's meant to answer: what do the park's bats do in winter? Nobody knows — and winter is when they're most at risk from white-nose syndrome (WNS), a fungal disease that attacks bats while they hibernate. WNS was first seen in Washington in 2016; at least 150 cases have turned up in the state since.

Where bats hibernate in big groups, whole colonies can be infected and die off. In the Pacific Northwest, many bats hibernate alone or in small groups; some species leave for unknown places, others may stay active all winter. Tracking single bats over long distances and long stretches of time is hard, so little is known. Wildlife biologist Rebecca McCaffery, who leads the U.S. Geological Survey's Olympic Field Station in Port Angeles and co-leads the project, says no one yet knows how the disease will spread here — or whether some places will be spared the worst while others see big declines.

A worldwide network

USGS scientists, working with the National Park Service, were fixing a solar-powered array of radio antennas to the spillway that day. It joins the Motus Wildlife Tracking System — named for the Latin word for movement — a network of more than 1,700 such stations (over 1,780 in 34 countries, by the network's own map).

• Any Motus receiver can pick up the signal from tiny transmitters called nanotags.
• Migratory bats caught at the former Lake Mills reservoir will each get a unique nanotag, so any tower they pass on their journey can log them. The bats move; the towers don't.
• Built for birds, Motus has since been used to study over 320 species of bats, birds, and even migrating dragonflies and butterflies. Now Olympic's tower can also catch far-travelling animals from elsewhere passing by.
• For bats that stay all year, the tower should show how often and how long they move as they settle into winter roosts — a bat that hides under bark for three days and comes out again will register.

A researcher fits a nanotag to a bat caught at the Glines Canyon Dam site. The tags weigh less than a paperclip and fall off after several months without harming the bat. USGS photo / McCaffery.

One piece of the puzzle

Since WNS reached Washington, parks in the North Coast and Cascades Network have stepped up bat work with the USGS:

• Listening: six parks — Mount Rainier, Olympic, North Cascades, San Juan Island, Lewis and Clark and Ebey's Landing — run permanent acoustic recorders that capture ultrasonic calls, later analyzed to identify species and behavior.
• Elevation: recorders along transects from valley floors into the mountains of Olympic, Mount Rainier and North Cascades picked up all ten resident species over two years, showing how each uses different elevations through the year.
• Early warning: each spring, colonies in Olympic, Mount Rainier, North Cascades and San Juan Island are tested for the fungus.
• Banding: at Mount Rainier, where one colony tested positive in 2017, park scientists and partners put light metal bands on bats' forearms. Recapturing banded bats gives a snapshot of a colony's health, and tissue samples help show how genetics may relate to survival.

Banding bats at Mount Rainier. Protective gear keeps diseases from passing between bats and people. NPS photo / Chestnut.

Above the Elwha

From the new station, the Elwha's larger comeback is in view: Chinook salmon run upstream to spawn and die, enriching creeks where dippers have rebounded over the past decade, and bats rise at dusk over young cottonwood, alder and willow on the old lakebed. Through the fall and winter, the antennas will log bats passing or roosting nearby and send the data over the cellular network to the Motus database. McCaffery calls it a thrill to find that such common species are still so little understood — and this is one piece of learning where the disease will hit hardest and what can be done.

More: what white-nose syndrome is and where it has spread; Motus and bat migration in the San Francisco Bay Area; the Motus Wildlife Tracking System.

Sources

Based on "Automated Radio Telemetry Will Shed Light on Olympic's Bats," Olympic National Park, National Park Service; a work of the United States government in the public domain. The Motus network's own map of its stations is not reproduced.