On the evening of Apr. 26, 2023, a little brown bat appeared at our place for the first time in more than a decade. Hunting for insects, it skimmed gracefully over the pond below our eastern Nova Scotia home. I hastily erected another bat box nearby, hoping that they would find it. Instead, the bat began roosting on the wall outside our bedroom window. After hanging in and flying over the pond for a week, it disappeared. We checked the window roost and found its dead body below, with most of its innards missing. Evidently a shrew had attacked and eaten it. Good for the wee rodent. Not so for the beleaguered bat, but nature took its course. 

White-nose syndrome’s arrival and spread
Two decades ago, someone who’d explored a cave in Europe travelled to see one in Albany, N.Y. They unwittingly imported dirt containing a fungus from the European cave, likely on boots or clothing.

The fungus, new to North America, was aptly named Pseudogymnoascus destructans. This fungus invades the skin of bats while they’re socially hibernating in caves, their immune systems dormant. The visitor left the cave, but the fungus remained to jump-start a bat pandemic that is still moving gradually across the continent. 

The white-nose syndrome fungus spreads steadily over hibernating bat bodies, waking them prematurely. Their heartbeat jumps from 20 beats per minute while hibernating to 200 beats per minute awake. They try to remove the fungus using energy needed to continue hibernation. Each arousal causes the bat to use up 30 to 60 days’ worth of fat reserves. Some bats venture outside to search for food. Instead, they find snow and no insects. They starve and die.

This disease, first noted in North America in 2006, kills an estimated 85 to 99.9 per cent of the population of each overwintering bat colony. From New York state it spread north and west, first detected in mainland Nova Scotia in 2011. It reached Cape Breton by 2015 and went on to New Brunswick and P.E.I., arriving in Newfoundland in 2017. It then spread west to Manitoba and beyond.

Year-round resident bats more susceptible
The Little brown bat, Northern long-eared bat, and Tri-coloured bat populations overwinter in caves in large numbers. At least, they used to. This disease hit them hard. Species not so affected are long-distance migrators. They stay active, spending winters in warmer climates. They don’t hibernate in caves in large groups. The Hoary bat, Silver-haired bat, Big brown bat and Eastern red bat have thus far avoided the deadly fungus. 

In Western Canada, bats prefer to hibernate alone or in small groups. They hide in tree cavities, crevices in tree bark or leaf litter on the forest floor instead of caves. So, they may also be less susceptible to the disease.

For centuries, bats have occupied a special ecological niche as the only mammals capable of sustained flight. They are a primary predator of night-flying insects such as moths and beetles and can exert considerable control over mosquito and black fly populations. One bat can catch hundreds of insects an hour, consuming 30 to 50 per cent of its body weight nightly.

Years ago, I visited several remote islands along our Atlantic shores, setting up mist nets as the sun began to disappear. Our group caught birds migrating at night and carefully removed them from the nets so we could band, record data, and release them. Those all-nighters occasionally necessitated removing entangled bats. I used to let the bats chew my hand (it seemed like a pacifier for them) while I untangled them from the mist netting. Then a Nova Scotian man got rabies after a bat bite. It’s a rare occurrence, but I stopped letting bats chomp on me. Be careful if you have to handle bats. Avoid disturbing or breathing in air associated with old bat poop. A mould on their feces sheds spores that can cause human respiratory problems.  

Disappearing habitats
Bats need mature forest habitats. These woods are quickly disappearing because of the pulp and biomass forest industry’s frenetic cutting, repeated every 40 years. Clear cutting results in satellite images with conglomerations of moonscapes covering vast areas of Atlantic Canada. The resulting monocultures are mostly devoid of the important roosting sites that older or dead trees provide in abundance. Healthy forests have plenty of features that bats can use, including holes in which to snooze throughout the summer day, or hibernate in the winter.

Trees become echo reference points when bats navigate in darkness using echolocation. For this reason they rarely travel over large, open fields. Bats rely on mature forests along lakes and waterways for insect foraging, roosting, drinking and migrating. Twenty and 30-metre-wide forested buffers left along rivers and lakes by clear-cutters are insufficient to feed and house bats. They fail to provide adequate nutrients to feed aquatic insect life in the waterway. Many aquatic insects emerge from the water’s surface and fly up into the air, creating fine dining opportunities for bats. Forested buffer widths of 100 metres or more are needed to supply appropriate wildlife habitat and offer the opportunity for use as treed corridors for migration.

Bat love
As biological pest control agents, bats are every farmer’s friend. A bat colony near gardens or crops can help control populations of cucumber beetles, moths, cutworms, corn earworms leafhoppers and June bugs. Bats even pollenate some plant species that need them for that purpose. Pesticides threaten bats. Direct spraying can kill bats, and chemical sprays kill theinsect populations that bats pursue.

There is recent evidence that East Coast little brown bat populations may be slowly rebounding. Breeding White-nose survivors become part of a natural selection process that promotes disease resistance in each subsequent bat generation. So, there’s some hope for the future of bats that occupy Atlantic Canadian caves.

You can help local bat populations. Stay away from caves, especially in winter, unless you know that there are no bats. Conserve old trees and dead standing trees. Protect vegetation along lakeshores, streams and rivers, and replant trees along waterways in wide swaths. Reconnect local forested areas by planting trees to make a corridor between them. Establish native plants in your garden to attract insects that are food for bats, and perhaps build or purchase a bat house to place on a tree or building on your land.

I hope our next returning little brown bat doesn’t get “shrewed” again.