Located in ƛ̓éxətəm Regional Park, just outside of Vancouver in Port Coquitlam, an unconventional housing structure has been established, featuring tall wooden boxes with narrow openings.
The only residents? Approximately 800 female bats.
Mothers, daughters, and grandmothers return to these bat boxes each summer to give birth and nurture their offspring. For over ten years, bat enthusiast John Saremba has dedicated his time to caring for this colony, ensuring the artificial roosts remain safe for the animals amidst various environmental threats.
“They are incredibly gentle and caring mothers,” Saremba shared with CBC’s What on Earth? host, Johanna Wagstaffe. “In fact, if a female bat is experiencing difficulties during pregnancy, other bats will rub her belly.”
This display of care made his discovery in July 2018 all the more tragic; upon checking the boxes as part of his routine, he discovered 65 deceased bats.
“I came out here and was just heartbroken,” he recalled. “I truly didn’t know how to respond.”
The very structures intended to protect the bats can become lethal, scientists warn, as climate change leads to increasing frequency and severity of heat waves. During such events, the boxes can retain heat, exposing the bats to dangerously high temperatures.
However, abandoning bat boxes is not the solution—these creatures are already facing threats from disease and habitat destruction—yet as global temperatures continue to rise, conservationists argue modifications are necessary for the boxes.
A view looking straight up into one of the bat boxes on site at ƛ̓éxətəm Regional Park in Coquitlam, B.C, which contains about 400 bats in just one of the very large boxes at the time. (Submitted by John Saremba)
What exactly happened in 2018?
This incident was not the colony’s first encounter with dangerously high temperatures; they had managed to survive a heatwave just a month prior to the fatalities. So, what made this event different? And if conditions became intolerable, why didn’t the bats simply leave?
Leah Rensel, a PhD candidate in wildlife biology at the University of Montana, was conducting research on the Port Coquitlam bats at the time of the die-off.
“The temperatures inside the bat boxes had surpassed 44 C, which is fatal for this species,” Rensel stated.
Rensel believes that the bats’ strong maternal instincts contributed to their decision to remain, noting that the colony was likely undergoing parturition in July 2018, a period when the females congregate to give birth.
“[The babies] are very tiny … so the bats had these vulnerable pups and they were reluctant to abandon the roost, despite the extreme heat.”
While expectant mothers generally seek warmer areas to focus on giving birth, nursing, and hunting insects rather than regulating temperature, there is a threshold for how much heat they can withstand.
“I refer to it as the Goldilocks zone,” Rensel explained, which lies between 35 C and 41 C for both the little brown bat and the Yuma Myotis bat.
“It’s not too hot and it’s not too cold … so if you’re a bat in a maternity colony and you find a roost that consistently maintains that range, it’s perfect.”
Unfortunately, these small wooden boxes can heat up rapidly, especially when they are painted black and exposed to direct sunlight, as was the case with the Port Coquitlam boxes.
A cluster of bat boxes housing female Little Brown and Yuma Myotis bats in Səhətləm Regional Park in Port Coquitlam. (Submitted by John Saremba)
The interplay of elevated temperatures and the stifling conditions within the boxes leads to humidity, which poses a serious threat to the bats.
“What climate change is doing is essentially heightening the temperature aspect of their microclimate,” explained Cori Lausen, director of bat conservation with the Wildlife Conservation Society Canada and Rensel’s thesis advisor.
“When temperature and humidity combine, that results in heat stress,” she noted, adding that bats do not sweat, complicating their ability to cool off.
Why bats are in danger
Bats face threats from more than just extreme heat.
Globally, habitat destruction and forest fragmentation have diminished the availability of natural roosting locations and the insect-rich environments that bats depend on for sustenance. In North America, the fungal illness known as white-nose syndrome has severely impacted their populations.
Out of the nearly 1,400 bat species worldwide, 25 are classified as critically endangered, 87 as endangered, and 110 as vulnerable, according to the International Union for Conservation of Nature.
A world devoid of bats, or with significantly diminished populations, could lead to catastrophic consequences for ecosystems, as these creatures play a crucial role in natural pest control, regulating insect populations that threaten forests or agricultural lands, as outlined in a 2019 study published in the journal Biodiversity and Conservation.
In tropical and subtropical forests, bats assist in seed dispersal through their droppings, playing a vital role in ecosystem regeneration.
Furthermore, the implications of losing these winged mammals may extend even further: one peer-reviewed study indicated that in areas where bat populations declined, pesticide usage increased—resulting in higher infant mortality rates.
Sixty-five bats were found dead inside a home built to protect them. What went wrong? A surprising bat housing crisis reveals how a warming climate is changing the places bats call home. From devoted bat moms, to dangerously overheated bat boxes, and some equally surprising solutions — including bat condos with emergency exits and artificial tree bark.
So, what’s the solution?
Lausen proposes that the key is not to eliminate bat boxes but to increase their number.
“Never remove a box, never alter a box,” she advised. “Instead, add boxes around your property to provide them with more choices.”
She suggests spacing boxes no more than 100 meters apart, enabling bats to easily switch roosts as needed for temperature regulation.
“Establish a nice assortment of bat boxes: varying sizes, styles, and levels of solar exposure.”
This could involve boxes with different ventilation systems or paint colors, which can influence how much heat they absorb, according to Lausen. She emphasizes that a minimum of three bat boxes should be present on each property.
Another innovative solution is a “bat condo,” Lausen mentioned, featuring various compartments so that bats can transition between microclimates without leaving their roost, similar to how city bats have traditionally inhabited attics.
The first bat “mini-condo” designed to hold 1,000 bats built in a regional park in Metro Vancouver. In a bat condo, bats can move between different microclimates without having to leave the roost. (Submitted by John Saremba)
In British Columbia, Saremba has been working with both old and new bat houses. He has applied shading to the older boxes using white blankets and created emergency exits from PVC pipes.
Since implementing these modifications, bat mortality has ceased.
Additionally, he has constructed a mini condo designed to simulate an attic environment, providing bats with more space, temperature variations, and humidity levels to choose from.
This structure even includes areas for young bats to practice flying.
“It’s akin to a teenager learning to drive,” Saremba remarked. “You don’t immediately hit the highway; you start on the side streets.”