You may not give a pile of bats collected over 4,300 years a second look – but a group of scientists has been given an intriguing look at how bats’ diets and therefore climatic conditions have changed over thousands of years.
Taller than the average person (2 meters or 6 and a half feet), the pile of kaka (also known as guano) records history in clear layers, like sediments under a lake.
By analyzing the layers back in time, scientists have been able to understand the changes in the diet of bats that have inhabited this cave for millennia.
In turn, dietary changes hint at what the climate and environment may have been like during this time, with variations in temperature and rainfall affecting animal life and the species of insects and plants that were available to bats to eat.
“We study natural archives and reconstruct natural histories, mostly from lake sediments,”
The researchers were particularly interested in sterols, biochemical markers of the diet produced by plant and animal cells. These sterols pass through the digestive system and can be preserved for thousands of years – as was the case here.
An analysis was also made of some of the bats that currently live in the same place: the Home Away from Home cave in Jamaica, which is currently home to about 5,000 bats of five different species. This gave the team a baseline to work against.
Researchers found a jump in plant sterols in the bat diet about a thousand years ago, researchers found, corresponding to the medieval warm period (900-1300), when America was thought to be particularly dry.
Another surge in plant sterol was discovered around 1350 BC, at a time known as the Minoan warm period. Dryer conditions usually make life difficult for insects, and during these times bats ate fruit more often for breakfast.
“From our results, we concluded that the climate in the past has affected bats,” said biologist Laurent Galant of the University of Ottawa. “Given the current climate change, we expect to see changes in the way bats interact with the environment. This could have consequences for ecosystems.”
Another interesting finding is the changes in the carbon composition of guano, which probably correlates with the arrival of sugar cane in Jamaica in the 15th century. Chemical signatures of human activities such as nuclear tests and the arrival of lead gas can also be observed.
Bats are more important to ecosystems than you might think: they control insect populations, pollinate flowers and scatter seeds. This cave method is a non-invasive, effective way to study their diets and check their well-being throughout history, which – with the right pile of guano – can stretch back thousands of years.
It is 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 the same information about climate over time.
“As part of the work showing what you can do with poo, this study is breaking new ground,” said geologist Michael Byrd of James Cook University in Australia, who was not involved in the new study.
“They’ve really expanded the tools that can be used for guano deposits around the world.”
The study was published in Journal of Geophysical Research: Biogeosciences.