Two Million Bats and a Wind Farm: A Maternity Roost in Nevada's Spring Valley

First published in The Midden, the Great Basin National Park newsletter, Vol. 22, No. 1, Summer 2022. By Bryan Hamilton, acting Integrated Resource Management Program Manager.

A common bat, often overlooked

Joey Danielson, Kelsey Ekholm and Bryan Hamilton published a peer-reviewed paper on Mexican free-tailed bats in the journal Population Ecology.

These bats are among the most abundant mammals on Earth, and they eat huge numbers of insects:

• They're worth $23 billion a year to U.S. agriculture.
• A single colony in Texas was valued at over $3,000,000 a year in pest control.

Yet, like many common species, they're often ignored by conservationists and biologists — and a major new threat is rising: wind energy.

The wind energy threat

Wind energy facilities kill millions of bats worldwide every year. Migratory, high-flying, open-air feeders like the Mexican free-tailed bat are at high risk from turbine strikes and barotrauma. Two studies at wind facilities near large roosts, or where the species is concentrated, found it made up most of the dead bats — 85% and 94%.

Reducing those deaths takes knowledge of the affected bats' biology, which often doesn't exist, especially for common species.

What they found

The team studied a big roost in eastern Nevada used by two million bats — just 6 km from a 152-MW industrial wind energy facility.

• Over 5 years, they caught 46,353 bats in a harp trap.
• Just over half (53.6%) were non-breeding adult males.
• But they also caught 826 pregnant, 892 nursing, 10,101 finished-nursing and 4,327 non-breeding adult females.
• Juveniles were 11.5% of captures.

Pregnant and nursing females and young mean this is a maternity roost, of real ecological and conservation value. The authors know of no other industrial-scale wind facility this close to a heavily used bat roost anywhere in North America.

What's next

• Keep watching the site: more is needed on bat deaths there and on how well mitigation works. The facility's operator, Pattern Energy, has been an excellent partner in protecting the bats, and the team hopes to publish that work.
• Track migration: almost nothing is known about where Mexican free-tailed bats migrate in the Southwest, and California in particular. The team hopes to use the Motus network of radio receivers to find out — knowledge that could guide where wind facilities are built and how to cut deaths locally.

Read the paper in Population Ecology.

More from this issue of The Midden: Results of the 2021 Christmas Bird Count · Lint Camp recap.

Sources

Based on "Bats in Spring Valley," by Bryan Hamilton, The Midden — Great Basin National Park, Vol. 22, No. 1, Summer 2022, National Park Service; a work of the United States government in the public domain. A photograph credited to a co-author by name only is not reproduced.