The bats are back. It has been a while, but this summer at dusk it was good to see the bats manoeuver as no other mammal can.
Often portrayed as a spooky fall decoration or a feared blood-sucking creature, these depictions give bats a bad reputation. One bat can consume over 3,000 insects every night, keeping insect pest numbers in control. Bats save the farming industry millions of dollars on pesticides every year.
Christina Davy has been a research scientist with the Ontario Ministry of Natural Resources and Forestry since 2016 and directs a conservation ecology lab at Trent University. Her research program focuses on wildlife species at risk, particularly bats.
“I was introduced to bat biology in 2003, and I have been fascinated by bats ever since. A key part of my research program focuses on bat habitat requirements, on understanding threats to Ontario bats, and understanding how we can recover bat species at risk in Ontario. As part of this work, my team and I are tracking the effects of white-nose syndrome (WNS) on Ontario bats.”
In 2006 a previously undescribed disease was observed in bats hibernating in a cave in New York State. The bats had fuzzy white fungus growing on their noses, ears and wings, which biologists had not seen there before. The disease was named white-nose syndrome, and scientists found that it is caused by a fungus called Pseudogymnoascus destructans, which was introduced to North America from Europe (probably by cavers).
The fungus grows well in cold, humid conditions – like on a hibernating bat. It causes lesions (little sores) on the bats' skin and causes them to wake up more often during hibernation than they normally would. As a result, some bats with the disease use up all their fat stores before the spring and starve to death. Since 2006, bats have carried the fungus from one cave to another allowing it to spread through most of the eastern US, and into Atlantic Canada, Quebec, Ontario, and Manitoba. It has killed millions of hibernating bats since it was introduced to North America. In Ontario, there have been recorded declines of 95-100 per cent of hibernating bats at some hibernation sites.
In Ontario, WNS has now been confirmed from the south-eastern part of the province to the north-west.
“We observed declines of approximately 95 per cent at the hibernation sites that we monitor after the disease arrived. And we've found that some species, like the northern long-eared bat, have declined to the point where we barely catch any anymore. But on the bright side, we do have growing evidence that surviving populations are persisting, especially in the little brown bat – so I am cautiously optimistic.”
She said it is too soon to say whether recovery of these remnant populations will be possible, and the outcome will depend on, “how well we can support endangered populations as they recover. This recovery depends on ensuring that survivors have access to high-quality summer habitat so that they can successfully raise their pups.”
People often think of bats as "flying mice,” but in fact, their biology is very different.
One of the reasons little brown bat populations are so slow to recover from these catastrophic declines is that females have only one pup per year, which they give a great deal of care. Female little brown bats have to eat approximately half their body weight in insects each night to provide enough milk for their growing pup, which is born weighing approximately a quarter of the mother's weight.
These bats are also quite long-lived – a female little brown bat can live for over 40 years, although most probably don't live quite that long. With these low reproductive rates and the high amount of care mothers have to provide to their young, it takes a long time for bat populations to recover after a decline.
Despite their small size, bats travel across huge areas each summer. Late summer is known by bat biologists as "swarming season,” because it's the time of year when the five bat species that hibernate in Ontario travel across the landscape at night, visiting caves and abandoned mines that they can use as hibernation sites when winter arrives.
“These movements are what allowed the fungus that causes white-nose syndrome spread so quickly – the bats move large distances and can carry the spores from one site to another on their fur."
“One of my students (Lauren Hooton) tracked little brown bats in south-western Ontario and documented flights of greater than 100 km in a single night during the swarming season. We joke that the swarming bats are essentially bar-hopping, as these aggregations are also an opportunity for bats to mate, and individual bats visit a number of different sites over a period of several weeks. And if 100 km in a night sounds impressive – bat biologist Dr. Brock Fenton once banded a bat at a site near Renfrew, and then recaptured it only a few weeks later at a site near Thunder Bay!”
She is cautiously optimistic about the recovery of little brown bats. “I'm less hopeful about the northern long-eared bat. This used to be the second most common species we captured in our surveys. Now, we're lucky if we catch four in a year (out of several thousand bats in total) and it seems possible they could become extirpated (locally extinct) in Ontario.”
Bats and bat populations are monitored in a few different ways. Bats echolocate (emission of sound waves) when hunting insects or migrating across the landscape in the summer, and we can record these calls using ultrasonic microphones. Some studies have compared the number of echolocation calls detected before and after WNS arrived, to try and understand how large population declines have been.
“We can also count bats at maternity colonies by counting them as they emerge at dusk, or count bats in hibernation sites (caves and abandoned mines), and compare counts over time. Finally, we conduct mark-recapture studies that allow us to recognize individual bats when we recapture them. We mark bats in two ways: we can use tiny microchips, like the ones vets use to mark cats or dogs. Or, we give them a tiny aluminum armband with a unique number stamped on it. This allows us to recognize the bat again when we catch it a second time. These data also allow us to estimate bat population sizes, and track changes over time.”
The public can support recovery of endangered bat populations by being good stewards of bat habitat. Ontario bats eat insects, and they depend on access to wetland and forest habitats and healthy insect populations to provide them with enough food. They also require safe roost locations in which they can raise their young.
“So anything you do to maintain the health of your local environment will also help bats. If you have bats living in your home and you need to exclude them, you can provide alternate roost habitat for them by putting up bat boxes, to provide them with an alternate roost site (you can find information on how to do this effectively at this website). The public can also help us monitor bat populations by reporting bat sightings to the MNRF. And if you know of a bat roost, either in a building or a tree, please report it here. This work helps scientists to track overall trends and distribution of bats.”