Status: Endangered in Ontario since 2012. Federally endangered since 2013.
The little brown bat, also known as the little brown myotis, is a small bat with a wingspan of 22-27 cm and an average weight of 7-9 grams. These bats have short glossy light brown to chocolatey brown fur, with black wings, ears and tail. Little browns are often confused with the northern myotis who has a very similar appearance; however little brown’s outer ear structure is long, thin and rounded at the tip (the northern myotis has a pointed tip).
Diet: What do they eat?
If you hate mosquitos then you will love having the little brown around! In fact, these bats are known to eat mosquitos more often than other species (they also eat more species of mosquitos than some other native bats)! This is not only good news for our itchy arms, but is also good news for our health because little browns have been found to consumer 9 species of mosquito that carry the West Nile Virus! Other than mosquitos they also feed on spiders and insects including moths, mayflies, flies, beetles, and caddisflies. Spectacularly, males can eat half their body weight in insects a night while a lactating (producing milk for young) female can consume up to 125% of her body weight in insects in the same time! Little browns are most active a few hours after sunset and before sunrise.
How do bats locate their prey at night?
How exactly do bats catch tiny insect prey that are hard to see? Bats use a special technique called echolocation. This technique consists of the bat making very high pitched noises which sends sound waves out into the environment. These sound waves bounce off their surroundings and travel back to the bats ears. Bats are able to interpret these sounds as a 3D representation of what’s around them. Essentially, bats can “see” with their ears! FUN FACT: many other animals have been known to utilize echolocation such as dolphins and even some humans!
Habitat and Range:
About 50% of the global range of little browns occurs in Canada with the species being found in all provinces and territories except Nunavut. The remainder of their range is spread out over most of United States and into Mexico. Within Ontario, the species is widespread throughout south, including within the Land Between, but has also been detected in northern regions.
Little brown bats are a nocturnal (most active at night) species, so during the day they require an area to roost and sleep. Typically, little browns roost in tall trees (in cavities, under bark or amongst leaves), but they will also take advantage of abandoned or poorly maintained buildings and bat boxes. Interestingly, little browns can be found in a range of habitats including open fields and wetlands; however their favourites tend to be forested areas adjacent to water (these forested riparian areas are their number one choice) or closed canopy forests.
Biology and Life Cycle:
As for reproduction in Ontario, these bats will swarm for the mating season which begins in August. However, no pair bonds are formed as both males and females mate with multiple individuals. After mating season is complete, females overwinter pregnant and then typically give birth to one pup in spring or summer. Pups mature at different rates depending on sex, with females being sexually mature after one year, but males only after two years. Wild little browns tend have an average life span of 6-7 years, but there have been reports of individuals reaching 30!
Little browns tend to swarm, or congregate in large numbers, in the late summer or early fall at the entrance to their overwintering (hibernation) site. Typically in Ontario, little brown migrate short distances (35 to 550 km) between summer habitat and hibernating locations. Historically, these hibernating colonies consisted of hundreds of thousands of individuals, but these numbers have declined by 75-100% in much of the east due to white nose syndrome (will be discussed below). Regardless, little browns still tend to hibernate in groups (white nose syndrome has made solitary hibernation more common than previously) from late fall to early spring in caves, abandoned mines or wells where conditions are humid (greater than 80%) and temperatures remain above freezing (2 to 10 C).
Threats/Reasoning for Being at Risk:
1.White Nose Syndrome (WNS)
White Nose Syndrome (WNS), a deadly disease caused by a Pseudogymnoascus destructans fungal infection, is the greatest threat to the recovery of the little brown myotis. This foreign (coming from either Europe or Asia where bats have some immunity) fungus was first detected in North America in New York in 2006. Since then, it has caused widespread devastation to bat populations in eastern Canada and the United States (as can be seen in the map above).
The WNS fungus infects and grows on bat’s skin while they hibernate, causing severe damage to tissues and resulting in the development of white-grey patches of fungus on their noses, wings and ears (as can be seen in the photo above). As the infection progresses it results in bats having elevated metabolic rates which causes them to wake up from hibernation. This arousal results in the depletion of their energy stores which are required to survive the winter. As such, energy loss combined with the physical effects of the infection eventually results in mortality. Approximately 21% of the Canadian range of the little brown bat has been impacted by WNS, and populations at many known overwintering sites have declined by about 94%. Unfortunately, at some infection sites 90-100% of the little browns have died.
The WNS fungus thrives in the same humidity and temperature conditions required by hibernating bats. The spores of the fungus can remain viable in the hibernacula (where they are hibernating), as well as in the guano (accumulated feces) and soil, for many years even without the presence of bats. This fact likely severely impedes the ability of bat populations to recover at any previously used site. This deadly fungus is spread through bat-to-bat contact, bat contact with contaminated hibernacula, and human or predator movement from contaminated caves to non-contaminated caves (carrying the fungal spores with them as they travel). WNS appears to be spreading at a rate of 200 to 250 km per year! If this rate continues, it is predicted that all hibernacula in Canada will be affected by 2025 to 2028.
2. Wind Turbines
Death as a result of wind turbines is one of the largest sources of human-related bat death. These deaths result from collisions with turbine blades, or from injuries resulting from the sudden drop in air pressure (barotrauma) behind the turbines as a result of their spinning. An estimated 16 bats are killed per turbine per year in Canada. Currently, there are approximately 2577 wind turbines operating in Ontario which means an average of 41,232 bats are killed by turbines each year in Ontario alone! The little brown myotis accounts for 13% of all documented turbine-related bat deaths each year, with 87% of that 13% occurring in Ontario.
3. Predation by Cats
Predation by domestic and/or barn cats can pose a significant threat to bats. This is now especially true because their populations are already severely impacted by White Nose Syndrome. The little brown is one of the few bat species that roost in human-made structures. In particular, large groups of new mothers are known to use structures such as barns when nursing and training their young. Predation by cats around these and other roosting areas, particularly on bat pups, can have a significant impact on bat populations by removing the new individuals from the population. This increased rate of juvenile death results in a decreased number of bats being added to the next generation.
The spraying of pesticides, specifically neonicotinoid insecticides, in agricultural and forested areas has the potential to severely impact populations of the little browns by killing the insects that the bats rely on for food. Neonicotinoids are frequently found in wetlands and watercourses at levels well above the limit deemed acceptable by water quality guidelines! Many of the important food sources of the little brown myotis, such as mayflies and caddisflies, are aquatic and directly impacted by this water pollution. Furthermore, decreased availability of food can lead to reduced winter fat stores which impacts bat’s ability to overwinter effectively. This ultimately decreases their overall body condition and results in lower reproductive success and survival rates. The little brown bat is further impacted by pesticide pollution through poisoning from the consumption of insects contaminated by the toxins. These effects can further reduce the overall fitness of the bat, and its reproductive and survival success.
Current Conservation Efforts:
Due to the alarming decline in little brown populations conservation effects are underway throughout much of their range. Below are some ways conservationists are trying to minimize their threats.
1. White Nose Syndrome (WNS)
Lots of research on WNS is currently being conducted in Ontario and across North America into its causes, potential treatments and needed mitigation measures. However, at this time, no cure for the disease has been developed. In Ontario, a White-Nose Syndrome Response Plan has been created by the Ministry of Natural Resources and Forestry which outlines the government’s plan to detect, research and mitigate the disease. On an international scale organisations, such as the White Nose Response Team, are working tirelessly to advance research and educate the public about this deadly bat disease.
2. Wind Turbines
Some wind farms have been making adjustments to their turbines that minimize their impact to bats at times when the risk to bats is particularly high, such as at night during peak migration. These changes include periodic shutdowns of the turbines, increasing the minimum wind speed required to make the turbine blades turn, and arranging the blades to be more parallel with airflow to minimize the change in air pressure behind the turbines (reduces threat of bat barotrauma). These measures have been found to significantly reduce bat mortality (60 to 70%), with only marginal losses (1%) of power.
Several North American-wide bat monitoring programs and organizations (like the White Nose Response Team) have been created. These organizations are gathering data and information on remaining bat populations so that effective conservation decisions can be made across their range.
How can you help?
Bats are a very important part of ecosystems and provide excellent pest control! As individuals, we each have a role to play in bat conservation, especially those of us with waterfront and forested property! Below are some ways that you can help out our little brown bat friends!
- Report any sightings
- Avoid entering caves and mines where bats may be present, or where White-Nose Syndrome (WNS) is known to occur
- Traveling from cave to cave without properly decontaminating footwear and other gear can aid in the spread of the fungus that causes WNS.
- Keep your cats indoors
- Someone would not allow their dog to roam the neighbourhood so neither their should cat. Domesticated cats are a foreign species in Canada. Our native creatures are largely not adapted to deal with this elite predator! Cats are expert rodent and bird killing machines which are known to be a significant cause of bat mortality, particularly to young pups before they learn how to fly. Keeping your cat indoors, or on a leash, is imperative to help minimize bat fatalities associated with cat attacks.
- Provide habitat
- Consider attracting bats to your property by not removing standing live or dead trees (when safe to do so) that can be used as roosts and by putting up bat boxes. If you elect to put a bat box on your property, mount them on the side of a structure or on a pole/tree at least 10 inches above the tallest vegetation, as close to open water as possible, and in a location that receives at least 6 hours of sunlight per day. You can purchase bat boxes from The Land Between for $60 by clicking here! Interested in building your own? Check out these instructions by the Canadian Wildlife Federation.
- Coleman, L. S., Ford, W. M., Dobony, C. A., & Britzke, E. R. (2014). Comparison of radio-telemetric home-range analysis and acoustic detection for little brown bat habitat evaluation. Northeastern Naturalist, 21(3), 431-445.
- Kurta, A., Bell, G. P., Nagy, K. A., & Kunz, T. H. (1989). Energetics of pregnancy and lactation in freeranging little brown bats (Myotis lucifugus). Physiological Zoology, 62(3), 804-818
- Kunz, T. H., Braun de Torrez, E., Bauer, D., Lobova, T., & Fleming, T. H. (2011). Ecosystem services provided by bats. Annals of the New York Academy of Sciences, 1223(1), 1-38
- Thomas, D. W., Fenton, M. B., & Barclay, R. M. (1979). Social behavior of the little brown bat, Myotis lucifugus: I. Mating behavior. Behavioral Ecology and Sociobiology, 129-136.
- Wray, A. K., Jusino, M. A., Banik, M. T., Palmer, J. M., Kaarakka, H., White, J. P., … & Peery, M. Z. (2018). Incidence and taxonomic richness of mosquitoes in the diets of little brown and big brown bats. Journal of Mammalogy, 99(3), 668-674.
- Zimmerling, J. R., & Francis, C. M. (2016). Bat mortality due to wind turbines in Canada. The Journal of Wildlife Management, 80(8), 1360-1369.