Tagging Bats in Great Basin National Park Ahead of White-Nose Syndrome

Bats are worth a great deal to people. By eating agricultural pests, they provide pest control estimated at $40 billion to $53 billion a year in the United States alone. Yet human activity threatens them in many ways, and the most pressing threat in North America is disease. White-nose syndrome has killed millions of bats in the northeastern United States over the last decade, and the unprecedented deaths have led to several species being listed under the Endangered Species Act.

In 2015 the disease was predicted to reach White Pine County, Nevada, home of Great Basin National Park, within 10 years. That made baseline information urgent: which species live in the park's different habitats, which roosts they use locally, and how active they are through the seasons. Colonial bats that live in caves, several species of which occur in the park, are the most vulnerable, because of the climate inside caves and how closely packed their colonies are.

Park staff help the Nevada Department of Wildlife set up nets at a cave mouth during Nevada Batweek, an event to gather data on an area's bats, held in and near Great Basin National Park in 2015. NPS photo by Gretchen Baker.

Why bats are hard to study

Bats are active at night, which makes them hard to watch; they can fly across large landscapes quickly, and they roost out of sight, which makes them hard to follow. New research technology, usable for more and more purposes, is giving researchers powerful tools.

PIT tags

A passive integrated transponder (PIT) tag is a kind of radio-frequency identification (RFID). A transponder receives an "interrogating" radio signal and at once answers with a signal of its own — the same technology used to microchip cats and dogs, collect electronic tolls, open hotel locks and scan ski passes in a pocket.

Fish biologists developed PIT tags in the 1980s to follow the migrations of their fish, mostly in fresh water. The tag is a microchip sealed in glass. It has no battery: the electromagnetic field of a reader or antenna activates it (hence "passive"), and it replies with an alphanumeric code. In fish and other vertebrates the tags have proved a sound way to gather vital data, with no harm to growth or survival, though their use in bats is still fairly new. Each tag gives a reliable unique number, like a barcode, for the animal's lifetime, and the data can reveal sex ratios and age structure across a population.

For bats, tags on the fur or skin are easily lost, because bats moult and groom themselves and one another. A PIT tag goes under the skin. It is especially useful for cave bats: an antenna around a cave entrance reads each tagged bat every time it flies in or out.

The first season

In July, park biologists went to a workshop in Colorado to learn from experienced Colorado Parks and Wildlife staff how to insert the tags under bats' skin. Over the summer the park tagged 207 bats of seven species at nine sites. Several were recaptured later, confirming that the bats recovered from the implant; within a month of their first capture, many showed barely a trace of it.

The focus was Townsend's big-eared bat, which roosts only in caves and mines and is the commonest species in Lehman Cave. It is hard to catch in mist nets where it feeds and hard to pick up by sound — the two methods bat researchers rely on most — but trapping bats at their roosts as they came out worked, and more than 150 were tagged.

What the readers will show

A PIT tag reader and antenna now sit at Lehman Cave's natural entrance, and more are planned for other caves known to be roosts. They will show:

• how many bats use each cave;
• at what times of year bats use particular caves;
• how faithful bats are to a roost;
• the sex ratio of bats in each cave through the year, which can reveal maternity roosts;
• whether several species use a cave at the same time.

With so many bats tagged, researchers and managers hope to learn about their life histories and behaviour over the next decade. The work was paid for by the Park Service's Natural Resource Stewardship and Science white-nose syndrome response funding in 2014 and 2015.

Sources

• Dylan Rhea-Fournier, biological science technician, Bryan Hamilton, wildlife biologist, and Meg Horner, biologist, "Tagging Bats in Great Basin National Park," The Midden (Great Basin National Park), vol. 15, no. 2, winter 2015, National Park Service. https://www.nps.gov/articles/000/tagging-bats-in-great-basin-national-park.htm