2022 USA Cave Animal of the Year
The USA Cave Animal of the Year program enters its third year in 2022. This program brings attention to the amazing animals that live in caves and associated subterranean habitats. Many animals live underground in the thousands of caves that occur in the United States. As cavers, we are the visitors to their domain, and it is good to get to know our hosts a little better. What animal is the focus for 2022?
The USA Cave Animal of the Year is the Little Brown Bat (Myotis lucifugus).
Meet the 2022 USA Cave Animal of the Year: The Little Brown Bat
Little Brown Bats belong to the family Vespertilionidae, which is the most diverse (>400 species) and widely distributed bat family found in a variety of habitats in both tropical and temperate regions. Vespertilionid bats, often referred to as common, vesper, evening, or simple-nosed bats, are carnivorous and primarily insectivorous relying on echolocation to find and catch food on the wing. The Little Brown Bat is one of the most wide-ranging bats in North America and is known to roost in a plethora of locations from caves and abandoned mines to behind peeling tree bark and attics of homes. Historically, thousands of Little Brown Bats were known to communally hibernate in individual caves, but populations have dramatically declined due to White-nose Syndrome (WNS).
Getting to Know the Little Brown Bat
Little Brown Bats, also called Little Brown Myotis, are medium-sized bats measuring 8–9.5 cm (3.1–3.7 in) in total length with wing spans ranging 20–28 cm (7.9–11 in) and weighing just 6–12 g (0.2–0.4 oz). They have relatively long, glossy olive brown to dark brown fur on their backs that is lighter on the belly. The wing membranes, ears, and snout are dark brown. The ears are relatively short with a blunt and rounded tragus (i.e., the fleshy projection in the ear). Compared to other mammals of similar body size and weight, Little Brown Bats have a remarkably long lifespan, up to 31 years. Breeding takes place in autumn or early winter and females store sperm until spring when fertilization and gestation occurs. Females typically rear a single pup, which can fly on their own in about three weeks and reach adult weight about a month later.
Little brown bats are found throughout much of North America and can live over 30 years.
Where Can I Find Little Brown Bats?
Historically, Little Brown Bats were abundant throughout the forested regions of North America, ranging from Alaska and southern Canada southward to southern California, northern Arizona, and northern New Mexico in the western United States and to southern Mississippi, southern Alabama, southern Georgia, and northern Florida in the eastern United States.
Little Brown Bats are considered trogloxenes and use caves as hibernation sites during winter. Hibernation sites in caves, as well as abandoned mines, tunnels, and other underground structures, typically have high humidity, little airflow, and constant temperatures. Males and females will hibernate together and emerge in the spring to migrate to summer roosting and foraging areas in forested regions. In summer, Little Brown Bats use both natural and manmade structures as roosts, including under loose bark and in tree cavities, under bridges, in buildings, and in attics. Males typically roost alone while reproductive females roost together at hot and humid sites near water. Little Brown Bats are known to share roost with other species of bats. Some bats will travel hundreds of kilometers between summer roosting and winter hibernation sites.
What Do Little Brown Bats Eat?
Little Brown Bats are carnivorous and insectivorous specifically. They are voracious nocturnal predators feeding on many flying insects near water, such as mayflies, midges, mosquitoes, moths, and beetles. Nursing females may eat nearly half their body weight in insects during a single night! Little Brown Bats may travel up to 80 km (50 miles) a night to forage.
Threats to Little Brown Bats
Little Brown Bats are one of three bats most threatened by WNS, which is caused by the fungal pathogen Pseudogymnoascus destructans. Historically, Little Brown Bats were one of the most abundant bats in North America. Some winter hibernation sites housed tens to hundreds of thousands of bats. However, after the arrival of WNS in 2006 and subsequent spread across the continent, only tens to hundreds of bats use these same caves, mines, and tunnels as hibernacula – declines of 90–100%. WNS grows on the muzzle, ears, and wings of hibernating bats and causes them to arouse more frequently during hibernation, burning valuable fat reserves and causing dehydration that ultimately leads to starvation and death. Little Brown Bats are also threatened by deforestation, particularly the loss of large snags and hollow trees used as roosting sites in summer. Wind turbines may also result in mortality of migrating and foraging bats. Because Little Brown Bats are long-lived and females only rear a single pup during a breeding season, recovery from population declines is slow putting the species at an increased risk of extinction. Some models predict that the species will be functionally extinct in northeastern United States by 2026.
Researchers study little brown bats to monitor their populations and learn more about them. Photo by Jordi Segers.
Conservation of Little Brown Bats
Bat biologists continue to monitor populations through winter hibernacula surveys and summer acoustic surveys as well as targeted population assessments. Significant hibernacula are prioritized for conservation measures, which include cave gating and/or restricting visitation during the hibernation season to minimize disturbance. Likewise, patches of forest, particularly snags and trees used as maternity roosts, are prioritized for protection. The Little Brown Bat has been assessed recently as Endangered by the International Union for the Conservation of Nature (IUCN) and is currently under review for listing under the U.S. Endangered Species Act
Why are Bats Important?
Bats provide several important benefits to humans. These ecosystem services include insect pest control, plant pollination, and seed dispersal. For example, some estimates suggest bats save U.S. farmers over $20 billion each year in pest control benefits through reduction of insect crop damage and use of pesticides. Cave-roosting bats, including Little Brown Bats, are important links to the surface for many cave ecosystems. While much of the organic matter found in caves is washed in, the energy and nutrients obtained by bats and transported into caves ultimately becomes available to other cave organisms in the form of their guano and carcasses when they die.
Cave Animals of the Year from Other Countries
Countries that celebrate Cave Animal of the Year agreed to feature bats to celebrate the International Year of Cave and Karst which has been extended to 2022. If you’d like to learn about some additional cave-dwelling bats, you can find links on our website for the Cave Animal of the Year in other countries, such as Germany (Lesser Horseshoe Bat – Rhinolophus hipposideros), Italy (Common Bent-wing Bat – Miniopterus schreibersii), Australia (Ghost Bat – Macroderma gigas), and several others.
How You Can Participate
We need your help spreading the word about Cave Animal of the Year. First, please visit the website: https://caves.org/conservation/caveanimaloftheyear where you will find additional information about caves as habitats, cave bats, and past Cave Animals of the Year, including cave beetles and pseudoscorpions. Please share the website address with friends and on your Grotto social media. If you are lucky enough to find a Little Brown Bat while caving, help others see it and learn about these cave species. We invite you to take a photo of the bat and post it on the USA Cave Animal of the Year Facebook page. In addition, we encourage cavers to report sightings of Little Brown Bats to state biologists that are tracking and studying the species. Have another great year of learning about and helping to conserve habitat for the fascinating animals that make caves their homes!
Little brown bats are seen most often flying at dusk, when they start searching for their food, insects. They will consume huge amounts of insects every evening. Photo by Jordi Segers.
Past USA Cave Animals of the Year
Subterranean ecosystems are often divided into major ecological zones that differ in abiotic factors, such as light, temperature, and humidity. These factors influence the types and numbers of organisms that occur in a given ecological zone. Caves are the most well-known examples of subterranean habitats. Caves can be divided into three major ecological zones.
The entrance zone marks the boundary between the surface and subterranean habitats and usually contains more species as well as greater variation in abiotic conditions, particularly temperature and humidity, compared to other zones. This zone is confined to the immediate area around cave entrances where light penetrates. Many species of plants and animals can be found in the entrance zone.
The transition zone (also called the twilight zone), marks the transition from the surface to subterranean habitats and connects the surface-dominated entrance zone with the dark zone. The transition zone is characterized by decreasing levels of light and habitats that are influenced by surface environmental conditions to a lesser extent than the entrance zone. Few plants grow in the transition zone, but many species of animals can exist.
Finally, the dark zone is the section of cave that lacks light completely and where environmental conditions are the most buffered from surface variability (i.e., conditions are usually the most stable). This deep cave environment is characterized by perpetual darkness, nearly constant temperature, and high humidity that is near saturation. No plant growth persists in the dark zone, and animals that exist here represent species that are most cave-adapted.
Subterranean habitats also can be divided vertically into distinct regions based on depth from surface and saturation with water. Each of these zones may host distinct communities of organisms.
Nearest the surface is the epikarst zone, which typically consists of networks of flooded or partially flooded cracks and crevices in bedrock and exists between surface and lower layers of unweathered soluble bedrock. Epikarst communities are dominated by small aquatic crustaceans, such as copepods and amphipods, but can also include terrestrial species. Water percolates through the epikarst and eventually reaches the vadose zone that contains a cave stream. A cave stream may be entirely fed by water from the epikarst zone or may also be fed by a sinking surface stream.
The vadose zone is the unsaturated area between the epikarst zone above and the water table below. The vadose zone of a cave is the area that can be explored by non-diving cavers (that is, you don’t need SCUBA gear!).
Finally, the phreatic zone is the region of a cave system that is permanently saturated with water and often contains large cavities. Wells in karst areas often access groundwater within this zone. Ultimately water within cave systems emerges back onto the surface at springs or seeps.
The ecosystem underground has some important difference from an above-ground ecosystem. Light is generally very limited and often absent. Nutrients may be very limited, unless there is a stream running through the cave or lots of cave organisms, like bats, who deposit guano in the cave. Generally, cave ecosystems are seen as being simpler versions of above-ground ecosystems. There is still a lot to learn.
Adapting to Life In a Cave
Many different organisms can be found in caves and other subterranean habitats. Some are accidentally in caves, having wandered in, or fallen into a pit. These species are not adapted to living underground and will perish if they cannot find their way back to the surface. However, other species purposefully live in caves for some or all of their lives. These creatures must adapt to an environment that is dark, generally has stable temperature and high humidity, and often has low food and nutrient resources.
Some species visit caves only occasionally. They are considered temporary or transient visitors, or trogloxenes, that use caves for shelter, to raise young, or to hibernate. Although caves are important to trogloxenes, they cannot live their entire lives underground and must return to the surface at some point during their lives. Examples of trogloxenes include cave-roosting bats and cave crickets.
Other organisms are more permanent residents of caves and subterranean habitats. Some may be found only in the entrance or twilight zones. These organisms called troglophiles can complete their entire life cycles within caves but often do not exhibit morphological adaptations associated with life in total darkness. Troglophiles also can be found in many habitats on the surface. Some species of salamanders, spiders, and flies are good examples of troglophiles.
Finally, some organisms,troglobitesand stygobites, spend their entire lives in the dark zone of caves and other subterranean habitats. Many but not all of these species have evolved a suite of traits, termed troglomorphy, associated with life in the perpetual darkness of caves. These traits include loss or degeneration of eyes and pigmentation, elongation of appendages, and increased capabilities of non-visual senses, particularly touch, taste, and smell. Obligate cave species also tend to have slower metabolic rates and longer lifespans compared to their surface-dwelling relatives. Obligate cave species are broadly categorized according to habitat—terrestrial species are called troglobites (or troglobionts), while aquatic species are called stygobites (or stygobionts).