The Best Housemates: Cohabiting with Bats
A hoary bat in flight. One of the most commonly seen bats on SḴŦAḴ | Mayne Island.
What is the first thing you picture when you think of a warm summer evening in the Gulf Islands? Bats, obviously. Bundled in sweaters with tea and chocolate, we (the summer staff and Michael Dunn) sat by roost sites at sunset all summer counting bats as they emerged from shingles, shakes, and openings in roofs. As we sat and counted, we also monitored the Echometer, a device that slows down bats’ echolocation chirps to a frequency we can hear, and identifies the species based on their call. And of course we talked about how cool bats are. For instance, did you know that their chirps are as loud as a smoke alarm? They would deafen themselves if a flap of skin didn’t cover their eardrum when they chirp, and uncover it in time for them to hear the ricocheting sound wave.
Notes From the Field
Perhaps the first thing to know about bats in B.C. is how little we know about bats in B.C. For the past 10 years the Conservancy has participated in the BC Community Bat Program, which is a network of regional hubs for monitoring known roost sites located in buildings. Few, if any, natural roosts are included in the B.C. annual bat count and, at least on SḴŦAḴ | Mayne Island, we don’t know of any hibernation sites or natural maternal colonies.
What the counts do tell us is how many bats are utilizing a roost, what species are around, and how that changes over time. Every summer, the Conservancy monitors six building roost sites and completes four counts at each site, two in the spring before the pups come out, and two after. We also monitor six natural sites to record the ambient bats that prefer to roost in trees and cliffs. This year we recorded nine different species with the Echometer, with the two most common observations being the California myotis and hoary bat. You can hear what they sound like in this previous article. On average there were about 15 bats detected per roost this year, ranging from 1 to 45.
We noticed that the bats tended to use human structures more in the spring, and less as the summer progressed. We also observed them emerging from different sides of a structure from one count to the next. We speculate that daytime temperature changes throughout the season result in a change in the bats’ preferred roost sites as they seek features that are warmed by the sun in cooler temperatures, and shaded ones during the heat. Overheating in human-made structures can be fatal to bats, especially nursing mothers and their young.
Successful Cohabitation With Bats
You would be hard pressed to find a tenant that is not only clean, quiet, and happy in the tiniest room in the house, but also keeps the mosquitoes under control. Did you know that most bats will eat more than their body weight in bugs every night? Bat pest control services to the agricultural and forestry industries are valued at $75 an acre per year, amounting to an estimated $3.7 billion a year in the US alone. It is no question that they benefit us- the question is, how can we be good housemates with them?
British Columbia has the highest bat diversity in Canada, and nine out of the sixteen species found in the province are found in the Coastal Douglas-fir (CDF) zone, which makes SḴŦAḴ | Mayne Island critical bat habitat. Habitat features such as old dead or dying trees with hollow limbs and loose bark give bats places to roost. Understory plants give them places to forage, as some species glean insects off leaves. Open water, like ponds, sloughs, or ditches give them places to drink, and draws in the insects they eat. When natural roost features are lost, bats generally stay in the area but, as this study suggests, increase their use of human-built structures.
The first step to being a good housemate for bats is retaining or enhancing these natural habitat features on your property. Maintaining or installing a pond or leaving a large snag on your property is likely to be more helpful to bats (and other species) than installing a bat box. Here are a few more things you can do to help them:
If you find guano…
You’re probably familiar with white nose syndrome. Spreading quickly in Eastern and Central North America, it is a fungal disease that has a 90-100% mortality rate in infected colonies. No live bats in BC have been detected with the disease, but Pseudogymnoascus destructans, the fungus responsible for it, has been detected in the Kootenays and in Delta. Yuma and silver haired myotis, big brown bat, and silver-haired bat are species that have contracted the disease elsewhere in North America and are also found on SḴŦAḴ | Mayne Island. We have begun monitoring for it by collecting guano samples from roost sites in the spring and sending them into a lab for testing. Guano looks like an elongated mouse dropping and is found scattered along the base of walls where it has fallen from roosts. Along with checking for the fungus that causes white-nose syndrome, guano testing is the only way to confirm bat species identification. If you find a large amount of guano at your house, we would love to know!
If you find a live bat…
Bats roost hanging upside down above the ground, so if you find a bat on the ground, you can suspect that it is dehydrated, injured, or sick. It also may be a juvenile that fell from a roost or landed badly while learning to fly. Avoid handling live bats unless absolutely necessary. If so, wear thick leather gloves that a bat cannot bite through or scoop the bat into a container without touching it. Cover your mouth with a loose mask or fabric to protect the bat from any droplets from you (humans can transfer diseases like Covid-19 to bats). If you are scratched or bitten, a rabies vaccine is strongly advised. Keep in mind that less than 0.5% of bats carry the disease, but it is best to take the precaution.
If you find a dead bat…
If you find a dead bat on your property, do not handle it with your bare hands—use heavy leather or rubber gloves, place it in a sealed plastic bag, and then put it in a freezer. Please contact the Conservancy so that we can immediately collect the bat for testing and analysis. This study shows that cat predation is the most common cause of death for bats, so keeping your cats indoors when bats are most active can limit the number of casualties. Signs of white nose syndrome include sticky wing membranes, spots on wing or tail membranes, or visible fungal growth. If you observe any of these signs, let us know.
If you find a roost…
If you see 5 or more bats flying around your property and would like to get involved with the BC Community Bat Program, let us know! We are the local first point of contact (Report your bats | BC BATS).
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