Ancient cave poop reveals how bats have adapted to humans and climate change
Researchers studied guano as old as 4,300 years to see how bats' diets have changed over the centuries
Only a handful of people have gone inside a Jamaican forest cave that's frequented by bats. Among them are a team of researchers who studied the creatures' poop — and found it to be thousands of years old.
The team carbon dated the bat feces, also known as guano, which has been accumulating into a mound of excrement within the Westmoreland cave.
"We were able to go back around 4,300 years … [and] we didn't reach the bottom of the pile. So who knows how much more data is back here," biologist Lauren Gallant told As It Happens host Carol Off.
Gallant is a PhD biology student at the University of Ottawa, and lead author of the study, but she wasn't part of the team that explored the caves. She says guano can explain how bats lived and what they ate over time.
The findings were published in the Journal of Geophysical Research: Biogeosciences.
"We saw two periods where we believe there is increased fruit-eating relative to insect-eating amongst the bats," Gallant said. "Looking at historical climate data, we think that this might have been two periods of increased, warmer and drier conditions."
What that means is that the insect-eating bats could have switched to a fruit-based diet. Or a different species of fruit-eating bats could have entered the cave.
Based on the data, she says she believes the bats adapted to the warmer climate — which would not have favoured insects — by changing what food they ate.
"I think the biggest takeaway is just how much our activities can affect species, whether or not we're thinking about it. And it can be long-term effects," she said. "We're fortunate that the bats are able to bounce back and, you know, modify their diet as required. But not all species are able to do so."
Sampling the deposit
The cave, called Home Away from Home, does not usually get human visitors, as it is protected by conservation efforts. But the researchers were able to send a sampling team down "tens of metres" to where the guano deposit is located.
The deposit itself is large, sitting at about two metres in height. Inside the very humid cave, the sampling team excavated half of it in order to reach its centre.
They used their tools to take one centimetre interval samples of the guano and package them individually for testing later.
"They kind of worked their way down the core," Gallant said. "Then at one point … things just got too steep and cleaning the tools took a little bit too long.
"It was difficult, so they actually had to stop."
Human impact from afar
Last year, Gallant and her team studied the contents of the guano for any evidence of human impact.
"We looked at the concentration of metals in this deposit over time," she said.
Within the layers of guano, they found increased levels of cadmium, mercury, lead and zinc present during the same time as the Industrial Revolution.
"We actually see a very clear signal from leaded gasoline use, where it goes up as soon as the world started using leaded gasoline and then it declines once we stopped putting it on the market."
The guano deposit has much to share about the history and role of bats in the world, Gallant said.
"I think it's important we understand how they respond to the environment and we make sure that they're able to continue to provide these resources that we really do depend on."
Written by Mehek Mazhar. Interview with Lauren Gallant produced by Katie Geleff.