The secret lives of Vancouver’s ‘invisible mammals’ — and the race to save them

Aaron Aguirre works against the darkening night in Vancouver’s Vanier Park, raising finely woven mist nets with two assistants on the edge of a large, still pond swarming with mosquitoes. As tonight’s first bat skims past, he rushes off for more equipment in the back of his Subaru, where he keeps a portable lab and mobile radio-telemetry tracker. A streetlight reveals a bat emblem on the tailgate. “Yeah, it’s kind of a theme,” he says, pulling out yet another Rubbermaid tote.

With his battered straw fedora and muddied cargo pants, the young University of B.C. master’s student, investigating the effects of urbanization on bats, looks every bit a misplaced explorer as Vancouver’s iconic skyline rises elegantly behind him while families amble along the False Creek seawall.

“They have no idea there are hundreds of bats swarming around them,” he says with a smile. “We call bats the invisible mammal because people really don’t appreciate how many there are, right outside their front door.”

Aguirre’s urban bat project aims to find out just how many bats live in cities in the Lower Mainland, using a variety of methods to compare bat activity in parks like Vanier. The goal is to locate some of the bat’s elusive city colonies and identify the park features they find attractive. The findings, Aguirre and his fellow researchers say, could be used to promote more bat-friendly urban spaces as a deadly fungal disease approaches B.C.

Soon, the mist nets are bombarded with darting silhouettes. By 2 a.m., 37 bats have been carefully untangled, swabbed, logged and released. Aguirre singles out a large little brown myotis — an endangered bat — and his research assistants help him glue a radio telemetry tag to his back with excruciating care before he’s free to resume foraging.

The team has one week to find him before the tag falls off. On foot and by car, a days-long search locates the bat’s roost somewhere among towering apartment buildings in the West End, one of North America’s most populous neighbourhoods. “To be in a place that dense was really surprising,” Aguirre later says.

The project attracts attention over the following weeks, as the public learns how these creatures live — and thrive — among us. Skimming over our zucchini patches and roosting next to our bedroom windows, city bats labour through the night on insect patrol and pollination duty, creating a world where our Sunday night barbecues are pleasant and our lovely gardens bloom.

Understanding urban bats isn’t just an academic curiosity, but an ecological imperative. In 2022, traces of the fungus that causes the deadly white-nose syndrome in bats was found in B.C. guano (their droppings). While this hasn’t progressed into full-blown cases of the disease in B.C., the urban research team is spurred by an urgency to gather baseline data to inform future conservation strategies. Humans rarely notice the busy city skies at night. If the disease strikes, entire colonies could disappear — without anyone knowing.

White-nose syndrome is ‘the most catastrophic wildlife disease in the continent’s history’

In the winter of 2006, a spelunker in upstate New York made the grim discovery of a strange white fuzz amassing on the noses of hibernating bats. The caver’s photograph led scientists to Pseudogymnoascus destructans, a fungus harmless to bats in Asia and Europe, but which in North America caused many species to wake during hibernation, depleting fat reserves and leading to starvation, hypothermia and, almost always, death. Researchers believe a tourist travelling to an adjoining commercial cave unwittingly tracked in the fungus on their clothing. Given the vital role of bats in insect control, pollination and seed dispersal, scientists quickly understood the profound ecological ramifications of this tourist’s misstep.

White-nose syndrome has now spread to 40 states and eight provinces, killing up to 98 per cent of its victims. Three of the 12 susceptible bat species in North America have seen their colonies plummet by 90 per cent. 

For reasons still debated, B.C. has been spared, giving scientists nearly two decades to glean valuable insights from eastern die-offs. It’s sharpened their response capacity and helped forge key partnerships in preparation for the disease’s inevitable arrival. The looming threat has sparked a public awakening about the need for bat preservation, while also providing opportunities for research on this universally understudied animal.

At the forefront of this work is a groundbreaking treatment for what the lead researcher, Cori Lausen, once called “the most catastrophic wildlife disease in the continent’s recorded history.”

A ‘Robin Hood’ approach to try and save bats in Vancouver and beyond

As white-nose syndrome deaths swept westward, Lausen, who works for the Wildlife Conservation Society Canada, faced a problem. Early treatment theories looked only at eastern bats, which hibernate in large, known colonies, allowing scientists to treat every bat directly in one place. But in B.C., bats hibernate in small, elusive groups, so a new approach was needed.

Investigating problems. Exploring solutions

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Investigating problems. Exploring solutions

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Lausen proposed an ingenious solution: find microbes that inhibit the growth of the fungus and have the bats themselves deliver it to their scattered winter colonies, like medical couriers. She collaborated with researchers from McMaster, University of B.C. Okanagan and Thompson Rivers universities. Together, they tested all manner of microbes.

“Bee propolis was great,” Lausen recalls, “but we needed something that wouldn’t glue the bats’ wings together.” A breakthrough came when the U.S. Geological Survey identified a candidate from, of all things, a bat’s wing. Building on this, Lausen’s team isolated four microbes from the wings of three resilient B.C. bat species.

This probiotic cocktail, mixed with clay powder, was sprayed into maternity roosts where bats give birth to and raise their single pup. Rubbed onto the wings, it provided a first line of defence, with the bats then carrying the microbe to larger winter colonies. Trials at Metro Vancouver roosts were outstanding: more than 70 per cent of bats tested carried the microbes. 

“It’s the Robin Hood approach,” Lausen says. “The wing microbiome is rising to the top as one of the most important factors associated with white-nose syndrome. It’s playing a bigger role than we ever imagined.”

It’s not a cure, but a boost to natural defence. Just as probiotics in yogurt improve the human gut microbiome, Lausen’s remedy boosts bats’ wing microbiomes. B.C. was an ideal location to develop the remedy, with its blank slate of controls and roost candidates in the Vancouver area. But the question remains: will the treatment work in the wild?

“How can we actually test if it’s helping bats survive white-nose syndrome?” Lausen asks. “And that’s the problem. We can’t.”

Even without definitive results, the program has received soaring support across the country. Universities, parks boards, wildlife centers, First Nations and all levels of government have rallied behind the effort with funding and logistical support.

The partnerships now extend south of the border, in a large but deeply coordinated response to the inattention of one tourist almost two decades ago. 

Implanted tags on bats transmit info to scientists

“It’s kind of amazing how big this project is,” says Chris Currie, a contract biologist on the probiotic project. 

At the Hayward Lake Recreation Area treatment site in Mission, B.C., Currie is implanting a tag under the skin of a little brown myotis. These “PIT” tags, passive integrated transponders, resemble metallic grains of rice and contain a microchip that transmits an ID number.

For years, Currie’s team has laboured at these treatment sites into the dark early-morning hours from mid-April to September. “We still don’t know why white-nose syndrome hasn’t spread here. At the normal rate, the fungus should have arrived in 2017,” he says as he raises a finely woven mist net into position.

The routine calls for each bat to be weighed, swabbed and sexed. Feces are also collected and all samples sent to McMaster University for genetic testing, evidence of the probiotic and the fungus. A tag is inserted before each bat is freed to resume foraging. But not a single bat inspected tonight, it turns out, will carry a tag from Currie’s previous visits. The reason why is one of many unexpected discoveries from this project — discoveries that may reshape our understanding of bat behaviour.

The Hayward Lake roost was once thought to contain a fixed population of 200 bats, but when the absence of transponder tags contradicted the assumption, researchers theorised the roost is less like a home and more like a hotel for 8,000 bats — called a metacolony. 

“It’s a much larger population that moves through a bunch of satellite roosts,” Currie says, explaining these secondary roosts allow bats to relocate when factors like temperatures or predators threaten their primary homes. This insight of the metacolony challenges previous assumptions and provides new, critical data for conservation strategies, emphasising the broader success of this research in safeguarding the populations and habitats.

The probiotic program has also unintentionally led to the longest-running study of the yuma myotis species — a smaller bat with black or brown fur — the significance of which has yet to be realised. 

“This dataset we’re gathering is so rich and goes beyond just the probiotic research,” Currie says. “We’ve got years of fine-grained population data ready to study.”

What the Hayward Lake bat metacolony can teach us

The discovery of the Hayward Lake metacolony highlights the need to understand bat dynamics across diverse environments. Early findings from Vancouver’s urban bat project suggest that a park’s size plays a much smaller role in attracting bats than its features, such as water bodies, fruit trees and interconnected ecosystems. As lead researcher Matthew Mitchell and Aguirre continue their work, the study raises important questions about how communities can create more bat-friendly environments, while also considering broader factors like climate change.

“How will that unfold when cities are already grappling with water shortages and considering draining ponds during summer?” Mitchell asks. “What will that mean for biodiversity — not just for bats, but also for the insects that feed birds and other species?”

“That’s the real gem of this study,” Aguirre adds. “It illuminates the rich research opportunities that urban bats provide, offering crucial insights into urban biodiversity and human-wildlife interactions.”

Public buy-in is the keystone of bat conservation. In the Lower Mainland city of Delta, biologist Danielle Dagenais is one of many regional coordinators with the non-profit BC Community Bat Program, or BC Bats. The program aims to bridge the gap between conservation science and the public through education and habitat protection.

“Why should we care about bats?” she asks a group of 15 gathered at the local library. They’re here for an evening bat walk, a guided tour through bats’ natural habitat. 

Before white-nose syndrome, urbanization, agriculture, pesticides and climate change had already erased many bat roosting sites, reduced insect populations and altered ecosystems. But the onset of the disease and subsequent media coverage catalyzed community bat programs across the Lower Mainland and beyond. Local residents started to care, creating safe places with bat boxes and vacant spaces in barns and abandoned buildings across the continent.

Locally, support surged when Richmond declared itself an official bat-friendly community, an initiative facilitated by BC Bats to help inform municipal policies. “That brought things into the spotlight,” Dagenais says. “When Port Moody and Delta followed, other municipalities started asking, ‘What can we do?’ ”

At the Delta library, some parents give their restless children permission to explore the library. Undeterred, Dagenais continues, dismantling stereotypes of bats, underscoring how humans rely on the often-understood mammal. Bats are prolific pollinators, propagating 500 plant species worldwide, including mango, avocado and cocoa, she says. Each bat eats about half its body weight in insects every night. Their poop is prized fertilizer. They are genetically closer to primates than rodents. No, they’re not blind — but their echolocation, a marvel of nature, can pinpoint an insect’s size, shape, density and direction of travel in complete darkness. Fewer than one per cent of bats carry rabies, with only three known human deaths in B.C. over the past century. 

A 2011 study estimated bats save American farmers more than $3.7 billion in annual agriculture losses. More recently, questioning whether declining bat populations actually reduce biological pest control, a University of Chicago study published in September found a 31 per cent increase in U.S. pesticide use following bat die-offs caused by white-nose syndrome. More tragically, even when insecticides were used within regulatory limits, these areas saw a 7.9 per cent rise in human infant deaths. 

The study also found farmers’ sales still dropped by 29 per cent. Combined with the cost of the pesticides, it amounted to $26.9 billion in losses between 2006 and 2017.

As the library talk ends, the parents are excited to ask about bat boxes for their properties. They stretch their limbs and collect their children before driving caravan-style to Boundary Bay Regional Park for the promised bat walk. The trail skirts a mosquito-rich marshland before winding through leafy tunnels and crossing streams to a lookout over the tidal flats. As twilight deepens, the bats tonight are few. But the occasional flutter against the darkening sky is unmistakable. The children, now sharply attuned, point and give chase; each sighting sparking shouts, laughter and questions.

Community bat programs promote conservation, but also align with frontline battles against white-nose syndrome, allowing scientists like Lausen to have thousands of eyes in the sky to help locate and monitor roosts. It also ensures that when a treatment is ready, a network of citizen scientists will be standing by to help deploy it.

That call to action may come soon. 

Arrival of white-nose syndrome in B.C. is imminent

 In 2016, the fungus that causes white-nose syndrome jumped 2,250 kilometres from the American Midwest to the Seattle area, causing more than 150 Washington outbreaks. The disease’s arrival in B.C. is imminent. In preparation, Lausen’s team partnered with the Washington Department of Fish and Wildlife. Last spring, they administered the probiotic in outbreak zones for the first time. Department biologist Abby Tobin has been at the forefront of the trials. “It’s really promising,” she says. “We know we’re not going to get rid of the fungus, but we can build resilience in the population.”

At a site affected by white-nose syndrome for two years, the probiotic — affectionately dubbed ”yogurt for bats” by the U.S. team — has shown signs of healing sick bats. Tobin notes public calls are responsible for 50 per cent of her responses. “It’s incredibly encouraging,” she says.

If successful, the probiotic will join the U.S. Fish and Wildlife Service’s arsenal against white-nose syndrome, alongside a U.S. Geological Service vaccine possibly ready within a year. While vaccines need direct delivery to each bat, the probiotic stands out for its ability to transfer independently from bat to bat. It is a key part of the continental solution.

Researchers still don’t know if the probiotic will work on species east of the Rocky Mountains, but expectations are high and discussions are underway to roll out both treatments simultaneously in the U.S. and Canada within the next two years. Until then, urgent work continues in B.C.

“The research here is still contributing for many reasons,” Lausen notes, including how factors like humidity, temperature and seasonal fluctuations affect the treatment’s efficacy. Biologists and citizens need to understand how local environments react to the probiotic, to maximize the odds of keeping these vital animals alive.

“We’re taking advantage of the time to answer all these other questions,” Lausen says. “The work we’re doing in B.C. is key.”