Flying by Night: USGS Scientists Put Technology to Work on Bats

How do you study something that flies under cover of darkness? This question persistently troubles scientists investigating the mysterious lives of bats. The 45 bat species that occur in the continental United States play important roles in U.S. ecosystems as major predators of flying insects and pollinators of desert plants. Bats also play an as-yet poorly understood role in disease transmission cycles. For these reasons, it is important to monitor the health of bat populations.

The cryptic and nocturnal habits of bats render assessment of their status difficult. To meet this challenge, USGS scientists at the Fort Collins Science Center are employing new technology to help answer previously difficult-to-answer questions to assess the health of bat populations.

In Fort Collins, Colorado, USGS biologists are using urban bat colonies to field test new methods of monitoring bat population dynamics in relation to rabies transmission. This is part of a cooperative study with Colorado State University and the Centers for Disease Control. Bats are marked with Passive Integrated Transponders (PIT tags) to assess their survival and movements. This is the first assessment of the status of bats in relation to rabies that follows known, marked individuals through time. Historically, marking bats involved attaching numbered bands to their wings, but this method can injure and disturb bats, and bands were often lost or rendered indecipherable. PIT tags are tiny electronic capsules that are permanently inserted under the skin of the bat and transmit information to remote sensors placed at roost entrances. When a bat enters or exits a roost, a computer records its unique identification information. Rigorous preliminary studies reveal no detrimental effects of PIT tags on bats, and the quality of information provided by this system will markedly improve efforts to monitor the health and status of bats.

In New Mexico, USGS biologists recently intercepted bats along their migration path in hopes of using technology to learn more about their distant travels. Several U.S. bat species make long-distance seasonal migrations and one of these species, the hoary bat, was the focus of the USGS bat migration study. This project drew on the expertise of scientists at the USGS Stable Isotope & Gas Chemistry Lab in Denver, Colorado, who helped analyze the stable isotope composition of small hair samples gathered from migratory bats. Isotopic "signatures" of hair were then compared to maps of isotopes in North American rainfall. Using this technique, the science team was able to determine the general areas where bats grew their fur and thus track their movements between summer and winter habitats. In some cases, hoary bats traveled more than 2000 km between seasons. The information gained and the new techniques developed during this study will help ensure the persistence of migratory bat populations.

Photograph of a big brown bat with a radio tag on its back.

In southern New Mexico, USGS biologists are again putting technology to work-this time to better understand the roosting and feeding ecology of two species of endangered long-nosed bats. Long-nosed bats migrate into the southwestern U.S. each summer to feed on the flowers and fruits of century plants (Agave) and various species of cactus with which the bats have co-evolved. While feeding from these plants, bats pollinate them and help disperse their seeds. Long-nosed bats must also find adequate caves and mines to roost in that are near their floral food sources. Loss of either food sources or roost sites could mean trouble for long-nosed bats in the Southwest. Like many of their colleagues, USGS biologists are using miniaturized radio transmitters to track activities and roosting sites of these bats. Smaller than a pencil eraser yet capable of transmitting a radio signal for kilometers, miniature transmitters have revolutionized bat research. By temporarily attaching radio transmitters to the backs of these animals, tracking crews can follow their nightly roosting and foraging movements across the Desert Southwest. For a species that can potentially fly over one hundred miles per night, radio tracking offers a practical solution to the problems inherent with following these nocturnal pollinators.

USGS-FORT biologists are continuing a legacy of bat research started early in the past century by predecessor agencies. By applying new technologies to old questions with elusive answers, the USGS is obtaining new and exciting information on this large and ecologically important group of mammals. Continuation of these efforts will help to ensure the proper assessment and future welfare of U.S. bat populations.