The story of Coastal Douglas-fir forests: All about bats

According to bat biologist Susan Dulc, if you have bats living in your attic or yard you should consider yourself lucky. Widely misrepresented and misunderstood, bats are fascinating creatures with an essential role to play in ecosystem functionality. Yet, most bat species in the CDF zone (and beyond) are under tremendous pressure and many are considered endangered. There are so many ways that we can help, including protecting habitat, keeping cats indoors, and holding decision-makers accountable to biodiversity protection.

What are some of the common bat species you might expect to encounter within the Coastal Douglas-fir biogeoclimatic zone?

British Columbia is the most biodiverse region in Canada for bats and out of the 16 species that you would expect to find in the province, nine of them are located in the Coastal Douglas-fir (CDF) zone. The most common species are little brown myotis (Myotis lucifugus) and big brown bat (Eptesicus fuscus). Other, less common, species include Yuma myotis (Myotis yumanensis), California myotis (Myotis californicus), silver haired bats (Lasionycteris noctivagans), Townsend’s big-eared bat (Corynorhinus townsendii), and hoary bat (Lasiurus cinereus), the last of which is one of the bigger bat species in the CDF zone. There are also a few smaller Myotis species, including long-legged (Myotis volans) and long-eared (Myotis evotis).¹

Interestingly, one unexpected species is the Brazilian (Mexican) Free-tailed bat (Tadarida brasiliensis). Breeding within BC is currently unconfirmed (status considered “accidental”), but it has been detected acoustically in summer on Salt Spring and on Vancouver Island near Cumberland.

To better understand bat populations and their habitat requirements, what are some must-know bat facts? 

In the summertime, the reproducing females of some myotis species, like little brown, Yuma, and big brown bats, form maternity colonies. They group together, sometimes in huge numbers (one known colony in Creston is composed of an estimated 2,500 bats) in what is called fission fusion society. According to scientists from Bat Conservation International, this is a social structure that has been observed in forest-roosting bat populations in Europe, New Zealand, and other parts of North America, as well as in some primate and whale species. The “fused” colony refers to a group of individual bats roosting together in one area and because that colony comprises more individuals than could possibly fit into a single roost (e.g. a tree cavity), the fused colony breaks into multiple subgroups. Those subgroups break apart during regular (i.e. every few days) roost switching with bats choosing different trees and sometimes different roostmates. This is the fission side of fission/fusion structure (Willis, Kolar, Metheny, & Brigham, 2005). ²

Though the reasons for this behavior are poorly understood, most scientists theorize that there are social components but the driving factor is the need to stay warm and the smaller energy cost to do this together. Not only is this thermoregulatory boost good for the adult females, but ideal for their young who stay grouped together when the females go out to forage. Ultimately, bats do a lot of work to stay warm. Most hibernating animals, like bears, prepare by packing on weight to store energy. But, because bats need to fly to survive, they live on the edge of a very thin line. They must have enough energy to survive, but not so much that they are unable to fly. 

However, not all bats form colonies. Each bat species has their own very specific habitat requirements and specializations. For example, Hoary bats roost solitarily among foliage of coniferous or deciduous tree limbs. Even within a species the roosting requirements in the summer will vary, depending on the reproductive status of the bat. Males (and non-reproductive females) typically prefer cooler roosts and tend to roost alone or in small bachelor groups. This facilitates use of torpor to save energy. Reproductive females typically prefer warmer roosts.

Other quick bat facts

• Bats are the world’s only flying mammals. They have the second highest species diversity of any mammal (~1400 species worldwide) with an equally impressive diversity of adaptations and specializations. 
• Bats are remarkably long-lived for such a small animal (a marked wild Yuma was recaptured nearly 40 years after initial capture!). They are also slow to reproduce with most species having only one pup per reproductive year. Unfortunately this means that, like many whale species, such as Southern Residents, bat population growth and recovery is precarious.
• Beyond their ecological importance, bats are beneficial to the human economy. For example, they consume agricultural and forestry insect pests. Estimates of the value of these insect control services run in the billions of dollars. 
• All of bats in BC are insectivorous, and most can eat more than their own weight in insects each night. This means, what impacts bug populations also impacts bats.  
• Many of the myths about bats are entirely false (e.g., flying into your hair, being blind, “flying mice”).
• Bats use echolocation to navigate, learn about their environment, find prey, and communicate. Mostly this is at frequencies beyond human hearing. When you see a picture of a bat with its mouth open, it is echolocating, not being ferocious and trying to bite anything!
• Some bats in BC are migratory while others hibernate.
• As the rest of this interview will show, there are still a lot of knowledge gaps to address regarding bats in BC. For example, there is still much to learn about population trends (likely decreasing for most species), hibernation locations, migratory routes, basic roosting ecology, habitat use, and maternity sites. Being small, nocturnal, and volant makes bats notoriously difficult to study.

What sorts of habitats on the Gulf Islands and Southern Vancouver Island are most vital to maintaining healthy bat populations? 

The best answer to this question is that we need to protect it all. Between the nine species in the CDF, there is a variety of preferred habitats, all of which are vital. As is the case with most wildlife, a diversity of habitats is needed to maintain a diversity of species. Habitat connectivity is similarly important. People might think that such tiny animals, that often use microhabitats, might not require access to large, connected ecosystems, but even small animals need connectivity. Like many small bird species, some bats do not like to cross open areas. They prefer to travel under the safety of the canopy or similar coverage. In my study area, which is in the Kootenay region, bat boxes were set up in a grassy field and the first thing the bats would do upon exiting the boxes was to head for the shelter of the closest trees. 

As far as specific ecosystem elements that many bat species require, roosting spaces such as crevices or cavities in wildlife trees and flaking bark, and older branches hidden by foliage are incredibly important. They also need foraging areas, which again differ depending on the species. Some forage by gleaning off of leaves, and thus need an understory. Others forage for insects aerially, so whatever habitat their insect-prey prefers is the kind of habitat aerially foraging bats depend on–oftentimes these are wetland and other still water habitats. 

Spotlight species: little brown bat

Little brown is a ubiquitous bat species throughout British Columbia, found in numerous biogeoclimatic zones, including in the CDF zone. They are quite adaptable and can be found in almost every habitat type including forests and open grassland habitats. They will roost in human structures where available due to the thermoregulatory benefits, with a seeming preference for older wood. They are aerial insectivores that often feed over open water and  within mature forest. Like most species, they will change their diet according to insect abundance over the course of the season.

Like many other bat species, when choosing natural features for roosting, older forests are preferred as characteristics of mature trees (e.g. loose, thick bark, deep cavities, etc.) provide more options. Connectivity of forests is also essential as a single tree will not sustain a maternity colony of bats for an entire season. They switch roosts frequently, often every two or three days, so just a few trees will not suffice. Sometimes, little brown bats are found in mixed species roosts. Here in BC, they are known to roost with Yuma bats.

Though little brown bats are one of the most common in BC now, given their vulnerability to White-nose syndrome (WNS) there is a high likelihood of extreme population decline (>98%). As a result, they are one of only two species in BC designated federally as endangered. Yet, at least half of the bat species in BC are known to be at-risk. Read more about the threats of WNS below.

This spotlight on little brown bats, one of the most common species in the CDF, demonstrates the diverse habitat requirements of every bat species.

Not only do many bat species, like Yuma and little brown, forage over water, but all drink on the wing (i.e. mid-flight), so still or slow-moving freshwater sources are essential to their survival. This is especially true of lactating females who require a higher volume of water and need the supply to be close to their roosts. Despite being such important sources of food and water, small ponds and streams are, unfortunately, not well-protected by provincial regulations.

Is population decline a significant worry in this region? If so, are there any species of particular concern? What are some of the major drivers of population decline?

Population decline for all local bat species is a huge concern, yet there is limited understanding of how these populations are doing to begin with. The BC Community Bat Program has established regional hubs that monitor known maternity roosts across the province, but those efforts are mostly focused on bats that make use of  buildings or boxes because that is how people have become aware of them. There are few, if any, natural roosts included in the Community Bat Program’s annual bat count. 

There is also the North American Bat Monitoring Program (NABat), which has been coordinating data (acoustic and other survey types) collection and analysis in a collaborative, continent-wide effort to monitor 46 species of bats. A number of locations in British Columbia are included in the program. NABat recently released summer occupancy analysis results (2016 – 2019) that indicates declines in occupancy probability of some species, including Little brown bat across their entire range.  Finally, Wildlife Conservation Society Canada (WCSC) has an established bat program led by Dr. Cori Lausen. Among other research and policy endeavors, WCSC monitors select hibernacula, like one outside of Nelson, and maternity colonies, like the bat condo in Creston. So, though there are some population monitoring efforts occurring, much of it is at a very local scale. There is still a lot that we do not know about bats in BC, and beyond for that matter.

Despite this uncertainty, there are certainly causes for concern including insecticide/pesticide use,  habitat loss, and likely most worryingly the impending threat of white-nose syndrome.

WNS is caused by a fungus, Pseudogymnoascus destructans or Pd, that was introduced to eastern North America around 2009. It has steadily been spreading westward since, with a detection in Washington in 2016 and another in Saskatchewan in 2022. When introduced to a bat population it is decimating. It has had devastating effects for eastern populations of myotis species like little brown bats, with populations declining by up to 99%. We expect that if/when it arrives in this region, it will have similar impacts for western myotis like Yuma. 

Most of the myotis species that are found living near humans, such as little brown bats or Yumas, do not have jaws powerful enough to break our skin.

Susan Dulc

In an effort to track the spread, there is ongoing surveillance for the fungus at a lot of local roost sites. The BC Community Bat Program also puts out an annual call for any dead bats found, usually between November and March. Those who find dead bats are asked to contact regional coordinators so they can be tested for Pd. Unfortunately, monitoring for WNS in this region is challenging, because unlike out east where cave systems are known and monitored, most western species are detected out on the landscape. However, because we do not know where most bats hibernate or where maternity colonies are, it is not possible to track where population declines may be occuring. That is where the findings of the NABat will be essential, because they can track a drop in acoustic records, which is more effective than searching for dead individuals on the landscape. 

Another threat to bat populations is an uptick in wind energy. Blade strikes explain about half of mortalities, but barotrauma (i.e.injury due to  changes in barometric (air) pressure) is also implicated. This is a challenging one to talk about as a transition toward cleaner energy is essential, but it is not without consequences. Based on the current number of fatalities occurring at wind energy facilities, population modeling suggests that Hoary bats will likely be near extinction within the next 50 years. There is research currently underway investigating what attracts bats to turbines and potential deterrents to prevent or mitigate fatalities, and I am hopeful that solutions will be found. But, I was recently at a conference where an expert, Dr. Erin Baerwald, pointed out we already know certain operational mitigations absolutely decrease bat fatalities – the problem is they just aren’t being implemented. So, though wind energy might be a good thing in the big picture, it is not perfect, and it is important to be mindful and critical to push wind energy facilities to do better.³

Why is it so common to find some bat species roosting in human-made structures?

Only a few species will roost in human-made structures (i.e. attics, siding, bat boxes, barns), and it is most commonly females that use these structures in summer. It may not actually be that common, but seems that way due to observational bias and probability. That is, it is easier for people to find/see bats in human-made structures than out in their natural habitats in the dark. For those species that do commonly use human structures, there are a few reasons why human structures might be used. These include: 

• energetic benefits (warmth good for reproductive females and juveniles)
• extra safety from predators (other than domestic cats)
• lots of space (can accommodate more individuals and gives pups a place to practice flying)
• landscape change (i.e., forest clearing may have removed the natural roosts that were previously used). When natural roosting options are limited, these may be the only alternative.

Roost and site fidelity is often high in bat species, so that they will re-use the same roosts and foraging areas every year as long as they are available. This can help explain why bats might move into a building after an adjacent forest was cleared, or why bats occupy bat boxes after being evicted from an adjacent house.

Some studies show that human roost areas are most important for reproductive females at higher elevations or more northerly latitudes with colder conditions. In these places, anthropogenic structures provide bats with a warm, stable place to raise their young, where otherwise they may have had fewer pups (or forwent reproduction entirely). However, this may change due to climate change as overheating events could lead to mortalities in structures like bat boxes. 

While there is limited published literature establishing a correlation between natural habitat loss and increased usage of human structures, this is a reasonable hypothesis. A 2014 study of bats in the Yukon provided some support for this theory when they found that females preferentially chose buildings for roosting over trees closer to their forage sites when forest habitat had been fragmented (Randall et al., 2014). 

What are your recommendations for conserving bat numbers in this region? Is there anything individuals can do to help stabilize populations in decline?

There are a lot of misconceptions about bats. This is likely partly due to the way they are depicted in the media, such as the commonly perpetuated myth that they will fly into your hair (fun fact: bats can detect something as thin as a single human hair, which is why capturing them is so challenging). Another common falsehood is that bats carry rabies, yet less than half of 1% actually do! In fact, the rabies virus is much more prevalent in other species, such as racoons and dogs, yet it is uncommon for people to fear or persecute these animals for being potential carriers. Further, rabies is only transmitted via bodily fluid (blood or saliva), so one would have to be bitten, or have an open wound that comes into contact with bodily fluid from the carrier. The rabies virus cannot survive long outside the body, so guano cannot harbour a viable virus. 

Bats, like most wildlife, want as little to do with us as possible, so unless you are handling a bat (which you typically should not be), you are extremely unlikely to be bitten. Plus, most of the myotis species that are found living near humans, such as little brown bats or Yumas, do not have jaws powerful enough to break our skin. A typical Yuma weighs as much as four gummy bears, so their jaws and teeth are tiny. Based on my experience, people who have bat boxes in their yard and regularly observe bats become fascinated and charmed by them. Because bats are nocturnal and hide in tiny crevices, most people do not get this experience. Like most things, what people do not know or understand, tends to scare them. 

That said, many people who are interested in protecting bats inquire about installing bat boxes on their property. While this can be a good option in some cases, a generally more efficacious action is to protect existing habitat. If creating or enhancing habitat is the only option, think “outside the [bat] box”. For example, installing a pond on your property is likely to be more helpful to bats (and other species) than installing a box they may never discover and use. It is important to note that such a pond does not have to be huge, even a small water feature that supplies clean water can be helpful to bats and the entire surrounding ecosystem. But, any habitat that you create – be it a bat box or a pond – will require regular maintenance if it is to be a safe and healthy place for wildlife.  If there are already bats roosting on your property the BC Community Bat Program needs to know about it. They have many good resources available and a Regional Coordinator for different parts of the province who can answer questions. I am also happy to be a point of contact, and if I do not have the answers I can put you in touch with people who do. 

Ultimately, the most important measure for protecting bats is to  protect their natural habitats, particularly those that have old trees. It is really the same story for all species: if you protect their habitat, they will be more resilient to all of the other challenges they face. 

If creating or enhancing habitat is the only option, think “outside the [bat] box”.

Susan Dulc

Another key thing people can do is to keep their cats inside. Free-roaming outdoor and feral cats are a huge problem, not just for bats, but also for birds, snakes, and other such species. I do not think that people recognize what a problem they truly are because when they are indoors they are sweet, domesticated animals. But it is instinctual behaviour. Cats will (and do) kill other animals. There have been studies that show that cats bring home something like 20% of their prey, so even if you think that your pet is not participating, it is you just don’t know about it. 

A recent publication showed that the majority of dead bats submitted to Abbotsford’s  Animal Health Centre for testing were killed by cats (Beattie et al., 2022). Unfortunately, female bats are disproportionately affected; because of their roosting requirements they are more likely to be associated with human structures where it is warmer, but also where they are more likely to encounter cats. So, not only are cats impacting the local current population but also future populations. There are many ways to enrich a cat’s life without allowing them loose outdoors, you can build enclosed catios or take them for walks. Further, studies show that indoor cats live longer lives, so keeping cats indoors is not just good for bats and other species, it is good for cats too. 

In the big picture, people need to be really mindful about the choices they make. Actions have consequences, and sometimes a cascade of consequences, some of which may not be immediately obvious. That is the way ecosystems work, and when one species is disrupted it resonates up and down the food chain. Two simple things each of us can do to reduce such impacts and make a difference for the species we hope to protect are 1) educate ourselves and 2) vote for those who represent our interests.  

About Susan Dulc

Susan Dulc is a resident of Pender Island and a master’s student at Thompson Rivers University (TRU),  working under the direct supervision of Dr. Karl Larsen (TRU) and Dr. Cori Lausen (WCSC). Susan is researching the thermal and humidity properties of artificial bat houses, and how they may or may not be providing suitable refuge for both little Brown and Yuma myotis bats (particularly breeding females and their offspring) during the summer months in the Kootenay region. Susan’s research helped inform new Best Management Practices (BMP) on using bat boxes; the BMP was a collaborative effort by  Canadian and US agencies and organizations and is currently under review. 

1. Randall, L. A, Jung, T. S., & Barclay, R.M.R. (2014). Roost-site selection and movements of Little brown myotis (Myotis lucifugus) in southwestern Yukon. Northwestern naturalist, 95 (3). 312-317. DOI: 10.1898/13-02.1
2. Willis, C.K.R, Kolar, K.E.,Metheny, J.D., & Brigham, R.M. (2005, Apr 26). Fission-fusion. Bats Magazine, 23 (1). https://www.batcon.org/article/fission-fusion/
3. Beattie, I., Schofer, D., McGregor, G., Lee, M.J., Lee, L.K.F., Himsworth, C.G., & Byers, K.A. An investigation of bat mortality in British Columbia, Canada. (2022). Canadian Journal of Zoology, 100(7). 464-473.DOI: 10.1139/cjz-2021-0230

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