You can’t look a second time a pile of bat poo collected over 4,300 years, but to a group of scientists it has provided an intriguing insight into how bat nutrition and with it climate conditions have changed over thousands of years.
Larger than the average man (2 meters or 6-and-a-half feet), the pile of poop (also known as guano) records history in clear layers, much like sediments beneath a lake.
By analyzing the layers over time, the scientists have been able to track changes in the diet of the bats that have inhabited this cave for millennia.
The dietary changes, in turn, provide hints as to what the climate and environment looked like at the time, with variations in temperature and rainfall affecting animal life and the types of insects and plants that bats could eat.
“We study natural records and reconstruct natural histories, mainly from lake sediments,” said limnologist Jules Blais of the University of Ottawa in Canada. “This is the first time, to our knowledge, that scientists have interpreted bat diets from the past.”
Thin slices of bat guano core. (Chris Grooms)
The researchers were particularly interested in sterols, biochemical markers of food produced by plant and animal cells. These sterols pass through the digestive system and can be stored for thousands of years – as was the case here.
An analysis was also made of poo from the bats that currently live in the same location: the Home Away from Home Cave in Jamaica, which is currently home to about 5,000 bats of five different species. That gave the team a baseline to counteract.
There was a spike in plant sterols in the bats’ diet about a thousand years ago, the researchers found – corresponding to the Medieval Warm Period (AD 900-1,300), when America was thought to be particularly arid.
Another plant sterol peak was found around 1350 BCE, at a time known as the Minoan Warm Period. Dryer conditions usually make life more difficult for insects, and during these times the bats ate fruit more often.
“We deduced from our results that the climate had an effect on the bats in the past,” said University of Ottawa biologist Lauren Gallant. “Given the current climate change, we expect to see changes in the way bats interact with the environment. That could have consequences for ecosystems.”
Another interesting discovery was changes in the carbon composition of the guano, which likely correlates with the arrival of sugar cane to Jamaica in the 15th century. Chemical features of human activities such as nuclear testing and the advent of lead-containing gas could also be observed.
Bats are more important to ecosystems than you may realize: they control insect populations, pollinate flowers, and disperse seeds. This cave method is a non-invasive, effective way to study their diet and monitor their well-being in a history that – with the right guano stack – can stretch for thousands of years.
It’s also worth noting that the same techniques used here can be applied to other caves around the world, the researchers say – which can be especially useful in areas without lakes and underlying sediments, which reveal much of the same information about the climate. time.
“As a piece of work showing what you can do with poo, this study breaks new ground,” said geologist Michael Bird, of James Cook University in Australia, who was not involved in the new study.
“They’ve really expanded the toolkit that can be used on guano deposits around the world.”
The research is published in the Journal of Geophysical Research: Biogeosciences