Bats

Mexican free-tailed bat flying in a cave just outside Great Basin National Park. This species also occurs in Sequoia and Kings Canyon National Parks.

Photo by Joseph Danielson, Nevada Department of Wildlife

About one-fourth of all mammals (nearly 1,000 species) on Earth are bats. Bats account for about 20 percent of the mammals in these parks, and many of the bat species (at least 17 of 25) in California use Sierra Nevada habitats. Bats are often misunderstood and underappreciated. But they play important roles where they live.

 

Townsend's big-eared bats roost in a cave in Lava Beds National Monument. Bats roosting in caves provide nutrients in their guano that helps support the growth of communities of cave organisms.

NPS / Shawn Thomas

Benefits of Bats

Bats benefit caves and other places they roost by providing important nutrients in their guano that can be used by other organisms. These parks have at least 275 caves, some of which provide roosting habitat for bats. Bats also roost on cliffs, in trees, under leaves on the ground, under bridges, and on buildings. Where they prefer roosting varies by species.

Sierra Nevada bats feed almost exclusively on insects, and bats are the primary predators of insects at night. Bats play a role regulating insect populations. When bats are around to eat insects, there are fewer insects causing damage to crops, and farmers don't have to invest as much in pesticides.

Just as some bats rely on thousands of insects each night for survival, other animals in the ecosystem rely on bats for their calories. Hawks, falcons, and owls eat bats, and mammals like weasels, ringtail cats, and raccoons sometimes attack bats while they roost.

In tropical and certain desert habitats, some types of bats eat nectar or fruit and play a role in pollination or seed dispersal.

 

Scientist Bill Rainey sets up a bat detector to record bat calls in the foothills of Sequoia National Park. A solar panel charges the battery that powers the bat detector, and bat calls are stored on a small memory card.

Photo courtesy of Elizabeth Pierson

How do scientists study bats?

Scientists who study bats need to be willing to work at night, when bats are most active. They use a couple different methods to detect or capture bats:

• Acoustic monitoring of bat calls – some species have distinctive calls that can identify them.
• Capture by mist nets that are stretched across meadows, streams, or ponds where bats forage for insects

Acoustic Monitoring

Scientists record the ultrasonic echolocation calls of bats flying overhead. Bats find food by emitting these high-frequency calls and using their sensitive hearing to detect echoes from flying insects and locate them. Some of the species have unique call characteristics (such as the call frequency, shape, duration, and pulse intervals) that can be used to identify species from the recorded data.

 

Bat Biologist Elizabeth Pierson sets up a mist net at Little Dog Lake in Yosemite National Park to capture bats and collect data about them during a 1990s research project. Bats are released after species identification, measurements, and other data are recorded.

Photo courtesy of William Rainey

Capture Techniques

There are a few ways scientists capture bats at entrances/exits to roost sites in caves as well as in areas where they forage for flying insects, moths, and other prey — such as streams, meadows, ponds, and ripiarian areas. In the bat inventory for these parks, scientists used mist nets set up in meadows, ponds, or streams to capture bats. They identify the species, weigh them, determine whether male or female, check their condition, and collect additional measurements before releasing the bats.

Please do not handle bats you find as they may be ill and you could be injured. Scientists also take precautions to avoid exposing bats to disease (gloves and masks) and being bitten.

 

What bats live in these parks?

Seventeen species of bats occur year-round or seasonally in these parks (see table below). Scientists Elizabeth Pierson and Bill Rainey conducted field surveys from 2001-2006, and also searched museum records and the scientific literature to document these species and their habitats. A combination of two field survey techniques were used to document these bats (described above): capturing bats in mist-nets stretched out in areas where bats forage for food, and acoustic detection that can identify distinctive calls of some species. This project was funded and managed through the Sierra Nevada Inventory & Monitoring Network.

The California Department of Fish and Wildlife lists the Townsend’s big-eared bat as a Species of Special Concern and a Species of Greatest Conservation Need. Its designation of S2 means it is considered imperiled, or at very high risk of extirpation (or local extinction). Four additional species have an S3 designation, or are at moderate risk of extirpation. See the following table for more information.

S2: identified by the California Dept of Fish & Wildlife (CDFW) as critically imperiled or at very high risk of extirpation (local extinction).
S3: identified by the CDFW as being at moderate risk of extirpation.

Bat Species Common Name	Scientific Name	Method of Detection
Pallid bat	Antrozous pallidus	Capture, Acoustic
Townsend's big-eared batS2	Corynorhinus townsendii	Capture
Big brown bat	Eptesicus fuscus	Capture
Spotted batS3	Euderma maculatum	Acoustic
Western mastiff batS3	Eumops perotis	Acoustic
Silver-haired bat	Lasionycteris noctivagans	Capture, Acoustic
Western red batS3	Lasiurus blossevillii	Capture, Acoustic
Hoary batS3	Lasiurus cinereus	Capture
California myotis	Myotis californicus	Capture
Small-footed myotis	Myotis ciliolabrum	Capture
Long-eared myotis	Myotis evotis	Capture
Little brown bat	Myotis lucifugus	Capture, Acoustic
Fringed myotis	Myotis thysanodes	Capture
Long-legged myotis	Myotis volans	Capture
Yuma myotis	Myotis yumanensis	Capture
Canyon bat	Parastrellus hesperus	Capture
Mexican free-tailed bat	Tadarida brasiliensis	Capture

 

Profiles of Three Bat Species

 

Pallid bat held in a gloved hand.

Photo by Keith Paul, US Fish and Wildlife Service

Pallid Bat

What do they look like?

This bat is pale (blonde to tan) with large ears, a blunt pig-like snout, and a skunk-like odor that may discourage predators. It is relatively large, 3.5- 5 inches (9.2-13.5 cm) from head to tail, and has a wingspan of about 13 inches (35 cm). The prominent ears have special traits that help these bats hear well and perceive sound through echolocation (emitting sound waves to navigate). Their large eyes and sharp vision help them locate prey at night.

Foraging Habits and Favorite Foods

These bats forage low over the ground in relatively open areas. They feed primarily on large, ground-dwelling prey – scorpions, Jerusalem crickets, cicadas, wolf spiders, centipedes, and some types of beetles. During nocturnal foraging, a pallid bat can consume up to 100 percent of its body weight in food!

Where do they live?

The pallid bat ranges from western Canada through the west and central U.S. and down into Mexico and Cuba. In these parks, pallid bats are most associated with low elevation blue oak woodland and mid-elevation black oaks, ponderosa pine dominated forests, and giant sequoia groves. To roost, they use tree hollows, rock crevices, caves, abandoned mines, and human structures such as buildings and bridges.

Migration/Hibernation

These bats do not appear to migrate any great distance as the seasons change. They break into smaller groups and hibernate deep within crevices of canyon walls, in buildings, or deep in caves. Not much is known about where they may hibernate in these parks.

 

Hoary bat, captured for a bat monitoring project conducted by the Mojave Desert Network in Joshua Tree National Park. Bats are monitored there for signs of the disease white-nose syndrome as well as species identification and general condition.

Photo by Sarah Barsch, Conservation Legacy and NPS Mojave Desert Network.

Hoary Bat

What do they look like?

The hoary bat is named for its distinct grey-white appearance. Their fur is very glossy, and a mixture of yellowish-brown, dark brown, and white – giving them their frosty appearance. They are 5-6 inches (12.7- 15.2 cm) long, and have a wingspan of about 15 inches (38.1 cm). They have a furry tail membrane that they wrap themselves in for warmth when they roost in trees.

Foraging and Favorite Foods

Hoary bats are relatively fast fliers with limited ability to maneuver through forests, so favor open areas such as rivers and streams, bodies of water, meadows, open forests, or over the tops of trees for foraging. They mainly feed on large moths but also eat other invertebrates such as butterflies, beetles, dragonflies, mosquitos, and termites.

Where do they live?

They are the most widespread bat in the Americas, with a range stretching from southeast Canada to Hawaii. Their range extends south to Guatemala, and from Brazil to Argentina and Chile in South America. In these parks, hoary bats are widespread, detected from the lowest to the highest elevations. While roosting sites in the park were not identified in this study, these bats are solitary rather than colony roosting species. They are frequently associated with riparian areas and presumed to roost in trees such as sycamore, cottonwood, and mature willow. When they roost, they typically hang from one foot and look like a dry leaf in a tree.

Migration/Hibernation

Instead of spending winter months hibernating in colonies, the hoary bats migrate to warmer winter habitats. After mating in autumn, females will move to the northern, eastern, and central United States to give birth, often to twin pups, in mid-May to early July. Males will remain in the mountainous areas of the western United States in the spring and summer, so it is primarily males of this species that has been documented in these parks. Some individuals may over-winter at the lower, warmer elevations of these parks.

 

Six Yuma Myotis roosting together against a wooden building and beam.

Photo courtesy of William Rainey

Yuma Myotis

What do they look like?

This is a relatively small bat, measuring 1.5 to 1.9 inches (3.9-4.8 cm) in head-body length, with an average wingspan of 9.4 inches (24 cm). They only weight about 0.21 oz (6 g). They vary in color across their range, and can be anything from dark brown to pale tan or even greyish with light colored fur on their underside.

Foraging and Favorite Foods

These bats typically forage over water in forested areas. They prefer forested edges of streams. They eat a wide variety of invertebrates, including moths, froghoppers, leafhoppers, June beetles, ground beetles, spiders, midges, mosquitoes, and various types of flies.

Where do they live?

The Yuma myotis is found throughout western North America, from British Columbia through Washington, Idaho, and western Montana, southern Wyoming, Colorado, New Mexico, West Texas and into Mexico. Yuma myotis reside in moist and dry forests, riparian zones, grasslands, shrubsteppe, and deserts, and are closely associated with rivers, streams, ponds, and lakes. Although their natural roosts include caves, rock crevices and hollow trees, they are more commonly found today in structures like bridges and buildings close to water. Tree cavities are important as nursery roost sites – where the mothers will shelter their young.

Migration/Hibernation

These bats are relatively inactive during winter, spending some of their time in torpor, but probably do not migrate any distance. While in torpor, they have decreased activity, marked by a reduced body temperature and metabolic rate.

 

What are major threats to bats?

Climate Change

In North America, extreme temperatures and drought are the biggest threats to bats from climate change. Heat waves and severe storms have already killed many bats, and these extreme events continue to threaten bats and other wildlife.

Disease

The disease White-nose Syndrome (WNS) is caused by a non-native fungus, and since its detection in New York state in 2006, WNS has killed millions of bats. Infecting skin and membranes of bats during hibernation, the fungus causes bats to be aroused too frequently, using up their fat stores and starving before the end of winter. Although not detected in the Sierra Nevada yet, it has been detected in northern California, Washington state, and New Mexico.

Habitat Loss

Loss of habitat means bats have less of the natural spaces and resources available that they need to survive and thrive. A few examples of habitat loss are:

• Destruction – Important habitats for shelter or prey are removed. Cutting down trees; development of open spaces for roads, buildings, or farms; and draining wetlands all reduce natural habitat for bats.
• Fragmentation – This happens when roads, farms, cities, and other development divide land. A space that used to be wide open and connected to other wide open spaces may now be isolated. This form of habitat loss is especially dangerous to bats, birds, and other migratory animals because it makes their traditional travel paths disappear or become more dangerous, with less food and shelter available along the way.
• Degradation – Some chemicals and other factors can cause an area to be unhealthy for bats and other wildlife, reducing the amount of appropriate areas for them to live. Examples of changes that can degrade habitat are pesticide use, too much artificial light at night (light pollution), or water contamination.

Wind Energy Production

Roughly half a million North American bats die each year from colliding with wind turbines. While wind energy production helps meet electricity demands with renewable energy sources, it can be made safer for bats.

 

Conservation

While bats face many threats and some are in danger of extinction, there is an increasing number of scientists and others working to protect these important animals.

Check out these tips to help protect bats where you live.

Although humans are not susceptible to white nose syndrome, we can spread the fungus that causes this disease between caves, mines, and other roost sites. Learn about precautions we can take to help reduce its spread.

 

Learn More

Bats in National Parks