Value of Bats in the Ecosystem
Temperate insectivorous bats serve important roles in many ecosystems, providing concomitant ecosystem services of benefit to humans.
- Insectivorous bats are very effective at suppressing populations of nocturnal insects, and some authors estimate the value of bats to the agricultural industry in the U.S. at roughly $22.9 billion each year through the suppression of insect pest species.
- Insectivorous bats are effective top-down predators of forest insects.
- In nutrient-poor environments bats can serve a nutrient “resets,” feeding intensely on aerial insects in nutrient-richer areas (e.g., riparian corridors, ponds, agricultural fields, etc.) and then transporting and depositing nutrient-rich material, in the form of guano, in nutrient-poorer upland roost sites or in caves. In some cases, bat guano may be the sole source of nutrient input for entire cave ecosystems.
Potential declines in populations of bats could have far-reaching consequences across ecosystems and biological communities.
Threats to Bats
Established threats to bats have traditionally include:
- Human destruction and modification of hibernacula and other roost sites,
- Pesticide use.
- Loss of important foraging habitats through human development and habitat conversion
However, recent emerging threats have impacted populations of bats at levels without precedent, eclipsing these traditional threats in at least the eastern United States.
- White-nose Syndrome (WNS), first observed in a hibernation cave near Albany, New York, in 2006, has been identified as a major threat to multiple bat species. The disease has swept northeast into Canada and south and west, first along the Appalachian Mountains and then into the Midwest, affecting most major bat hibernation sites east of the Mississippi River and killing an estimated 5.5–6.7 million bats in seven species. Documented declines of heavily impacted populations in the Northeast exceed 80 percent. How the disease will affect western bat species is uncertain. WNS is considered one of the greatest wildlife crises of the past century with many once common bat species at risk of significant declines or even extinction.
In March of 2016, a grounded Little Brown Bat (Myotis lucifugus) found near Seattle, Washington, tested positive for the WNS organism and later was confirmed to have died from the disease. Shortly after this event, the WNS organism was identified in a Silver-haired Bat (Lasionycteris noctivagans) from the same area. Since that time WNS or the disease-causing organism has been detected in a total of four Washington counties and the western states of South Dakota, Wyoming, North Dakota, and California. Western species confirmed to be WNS susceptible include Big Brown Bat (Eptesicus fuscus), Fringed Myotis (Myotis thysanodes), Little Brown Bat, Long-legged Myotis (Myotis volans), Western Long-eared Myotis (Myotis evotis), and Yuma Myotis (Myotis yumanensis). All these species have been detected at the INL Site through acoustic monitoring. Four additional species that have been detected at the INL Site (Brazilian Free-tailed Bat [Tadarida brasiliensis], Silver-hailed Bat [Lasionycteris noctivagans], Townsend’s Big-eared Bat [Corynorhinus townsendii], and Western Small-footed Myotis [Myotis ciliolabrum]) have tested positive for the white-nose pathogen in some portion of their range. Currently neither WNS nor the pathogen have been detected at the INL Site or in the state of Idaho.
- Wind-energy development is expanding rapidly across the western United States, and unprecedented mortality rates of bats have occurred recently at many of these facilities. Upper-end annual estimates for bat mortality from wind generation plants are approximately 900,000 individuals of mainly tree-roosting bat species; however, widely accepted estimates remain elusive.
Despite recent focus on emerging threats, direct impacts to hibernacula by humans remains the single most important conservation concern for bat populations in many areas.