← Back to Nature Notes

Nature Notes: Little Brown Bat

Ed Robinson
December 6, 2021

This is one of 40 wildlife essays found in Ed Robinson’s book, Nature Notes from Maine: Puffins, Black Bears, Raccoons & More. Click here for details.

If this story makes your skin crawl or your scalp twitch, don’t blame me. Lois made me do it.

You see, Lois is batty. I am not saying there is anything wrong with her belfry, she just loves bats. Lois insisted I had to write about bats. It is against my better judgement but Lois is a saint, so here it is!

The star of this story is the little brown bat (Myotis lucifugus). If you see a bat flying around your yard or field at night the odds are good that it is the little brown bat. If your hearing is better than mine you might also hear the high-pitched clicks and squeaks the bats issue when flying as part of their amazing radar system. With over 1,400 recognized species worldwide bats are the second largest scientific order of mammals, with over 200 of those species threatened with extinction. There are two families of bats in Maine, five species that roost in trees and three species including the little brown bat that make use of caves at least during winter hibernation. The rest of the year these social creatures are primarily found clustered in old barns and tree cavities.

I enjoy doing the research for these stories, filling the gaps in my knowledge, trying to find the latest statistics and doing my best to accurately portray the subjects. Yet I have this niggling fear that somewhere out there is a reader who will zing me if I mess up on their favorite creature. In book one of my Nature Notes from Maine series, I misstated a mineral in one chapter and sure enough, a good friend called me to account (gently!). I’m pretty sure the risk is low with this bat since most folk recoil from any mention of or encounter with bats just like they HATE snakes and spiders. I have seen grown women run shrieking into my cabin if a bat appeared overhead, not the least bit impressed that it is the only flying mammal on Earth!

If there is a creature in need of public relations help it is the bat due to dozens of myths and misunderstandings about them. To be polite, no bat is ever going to win a beauty contest. Only three bat species consume blood and none of them live within 2,000 miles of Maine. Despite old wives’ tales, bats are not blind, are not satanic pests and have no interest in attacking your hairdo. While bats may carry and transmit rabies via their saliva, biologists estimate that well under one percent of wild bats carry the virus. Your odds of contracting the virus are exceptionally small unless you are unlucky enough to have contact with a bat while sleeping or you handle the wrong bat without protective gloves. Bats are vital pollinators for hundreds of plant species around the world and they save America’s farmers billions of dollars in crop damage and pesticide costs each year.

The little brown bat is well named since it is only a few inches long, weighs less than one ounce and has a wing span around ten inches. The round ears place it in a family called mouse-eared bats. The fur is a mix of dark brown and cinnamon color with a gray undercoat. All four limbs are equipped with five digits and the front limbs on the leading edge of the wings function as both arm and hand. The mouth is small but equipped with 38 sharp teeth capable of securing hard-bodied insects in flight. The little brown bat ranges across the northern half of the US and southern Canada.

Bats have an amazing ability to fly in the dark and to capture prey on the wing. Using echolocation, bats emit high-pitched sound waves that strike objects and insects then bounce back to the bat’s ear. While hunting the bats emit up to 200 sounds per minute, allowing them to avoid collisions and to judge the location and the trajectory of an insect in motion. An insect may be plucked from the air by the bat’s mouth, or snagged in the wings and moved to the mouth by the claws on each wing. These acrobatic movements explain why the path of a bat in flight appears so erratic. In feeding sessions that last two to three hours around dusk and dawn, bats may capture hundreds of flies, wasps, mosquitos, beetles, midges and moths. They drink from the surface of a water source while flying and can snatch water-borne insects at the same time. Bats avoid flying in wet weather or when the temperature remains below 50 degrees F.

Breeding takes place from summer into the winter but females delay fertilization until they end hibernation. Pregnant females gather in nursery colonies, perhaps the same place of their own births. The normal late May to early July live birth is one pup but twins are possible. The pups are left hanging in the nursery when mothers feed but they quickly reattach to the nipple when mother returns. Within three weeks the pups are flying and are fully grown after a month. Predation is a factor at all ages as hawks, owls, cats and raccoons will take bats. During winter hibernation fishers and foxes have been documented eating dead bats off the cave floor.

From mid-April through October, bats need reliable food supplies and warm shelter. Old barns or sheds that are undisturbed are attractive haunts particularly if there are ponds, streams or fields nearby where large numbers of insects are available at night. A small hole or an open window in your house may allow bats to gain entry, so make sure your house is secure or you will be calling the pest control folks. As colder weather arrives bats either migrate to warmer climates or retreat to deep caves where they hibernate for roughly six months. There are thought to be just three major hibernacula in Maine that meet the requirements for consistent temperatures above freezing and enough moisture to avoid dehydration of the bats.

Studies of banded bats revealed migration routes of around 120 miles from summer habitat to winter caves. The bats hang from the ceiling tightly clustered to conserve heat, up to 300 bats per square foot. When hibernating the bat’s body temperature drops from 100 degrees F to a couple degrees warmer than the air in the cave, often just above freezing. Their pulse rate drops from 200-300 to around 12 beats per minute. The slower metabolism allows the bat to survive months with no food, drawing on a reserve of stored fat of just a few grams. The bats sleep for days or weeks, rousing only occasionally to drink from pooled water in the cave. Each time they wake, the bats burn a considerable amount of energy so it is vital that they not be disturbed by humans or predators during hibernation.

Unfortunately, the caves have become a death trap for millions of bats in the last fifteen years. Starting in the winter of 2006, cavers and researchers began to find dozens, then hundreds, of dead bats. All of the dead bats and many of those still alive had a thick growth of white fungus around their mouths and noses. Starting near Albany, NY the disease spread rapidly up and down the east coast, and then far to the west. Maine state biologists first documented the disease in Oxford County in 2011. Data indicated that in some caves over 98 percent of bats succumbed to the disease, creating a crisis for the little brown bat and several other species and leading to their designation in Maine as endangered.

Now identified as white-nose syndrome the fungal infection is caused by Pseudogymnoascus destructans, an appropriate name given the havoc it has caused. It is thought that the fungus arrived from Asia or Europe, perhaps on clothing or boots used by cavers. The fungus grows on the cave wall and migrates onto the body of the bat from where it can spread to neighboring bats. As the infection develops the bats wake more frequently in an attempt to clear their breathing passages, but the excess use of energy dooms them to death by starvation and freezing.

There is yet no cure for the fungus, but researchers are working to find one or a vaccine. One glimmer of hope is that some bats have survived, and it may be the result of ongoing genetic mutations that allowed the bats to develop resistance to the fungus before death. Researchers have also noticed small groups of bats hibernating in new winter habitats, on slopes with large collections of boulders and talus that provide shelter in deep crevices. The bats may be adapting in order to survive and rebuild their populations.

Maine’s Department of Inland Fisheries and Wildlife (IFW) has expanded it monitoring efforts in recent years to collect data on a creature that is very difficult to study. They have used acoustic studies and banding to track bats. The data is vital, both to protect bats and their habitats, but also to understand the impact of fewer bats on other species. For such small creatures, bats are surprisingly long-lived. While the average life span might be seven to ten years, one little brown bat lived 33 years.

To give bats a little help many people have begun in install purpose-built bat houses. At least two feet tall and one foot wide these houses provide options for bats as they move around in search of food and shelter. Painted black, with rough texture or screen to give the bats a foothold, these houses should be installed on a pole or the south side of a building high enough to keep ground-based predators away. Full sun exposure is ideal since the bats prefer a warm environment when raising their young and getting through the cold days of our shoulder seasons. You can easily purchase a bat house or make your own from plans found on the internet. Please note that protective clothing and masks should be used if cleaning up bat droppings (guano) since fungal spores may cause a lung infection.

Bats’ image took a big hit in 2020 when it was alleged that the virus behind the Covid-19 pandemic was harbored in an Asian bat before transmission into another creature that then passed it to a human. While bats are known to carry certain coronaviruses there has yet been no confirmation of the link between Covid-19 and bats. To help our bats recover from white-nose syndrome, state biologists are insisting that the public stay away from bat caves in winter. Careful cleaning of hiking and caving gear is an obvious requirement. A group called EduBat has developed trunks for every state that are full of bat education displays and games for teachers to use with young children.

To encourage Lois, I ordered a Haynes Bat Detector Construction Kit, a bargain at $35. Lois could take night classes to become a chiropterologist, one who studies bats. She can join other bat-bewitched folks in one of many bat fan clubs. Lois, I recommend Bat Conservation International, it is right up your belfry!