You may not give a stack of bat poop collected over 4,300 years a second look – but to a group of scientists, it provides an interesting insight into how bat diets and therefore climatic conditions have changed over thousands of years.
The pile of shit (also known as guano) is longer than the average man (2 meters or 6 and a half feet) and records history in clear layers, like sediments under a lake.
By analyzing the layers through time, the scientists were able to find changes in the diets of the bats that have lived in this cave for millennia.
In turn, the nutritional changes provide clues as to what the climate and environment might have been like during that time, with variations in temperature and precipitation affecting animal life and the types of insects and plants available for bats to eat.
“We study natural archives and reconstruct natural histories, mostly from more sediments,” says limnologist Jules Blais, of the University of Ottawa in Canada. “To our knowledge, this is the first time that scientists are interpreting bat diets.”
Thin slices of bat guano core. (Chris Grooms)
The researchers were particularly interested in sterols, biochemical markers of diet 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 has also been done of poop of the bats currently living in the same place: the Home Away from Home Cave in Jamaica, which currently houses 5,000 bats of five different species. This gave the team the basis to counter.
There was an increase in plant sterols in the diet of bats about a thousand years ago, the researchers found – corresponding to the medieval warm period (900-1,300 CE), when the Americas were particularly dry.
Another plant sterol peak was found around 1,350 BC, in a time known as the Minoan Warm Period. Dryer conditions usually make the insects more difficult to live, and during these times the bats ate fruit more frequently.
“We have deduced from our results that climate has had an effect on bats in the past,” said biologist Lauren Gallant, of the University of Ottawa. “Given the current climate change, we expect to see changes in how bats interact with the environment. This could have implications for ecosystems.”
Another interesting discovery was changes in the carbon composition of guano, which probably correlated with the advent of sugarcane in Jamaica in the 15th century. Chemical signatures of human activities such as nuclear testing and the arrival of lead gas can also be observed.
Bats are more important to ecosystems than you might realize: they control insect populations, pollinate flowers and disperse seeds. This cave method is a non-invasive, effective way to study their diets and examine their well-being in a history that – with the right guano stack – can stretch to thousands of years.
It is also worth noting that the same techniques used here can be applied to other caves around the world, say the researchers – which can be especially useful in areas without lakes and underlying sediments, which provide a lot of information about the climate during time.
“As a work that shows what you can do with poop, this study breaks new ground,” said geologist Michael Bird of James Cook University in Australia, who was not involved in the new study.
“They have really expanded the toolkit that can be used on guano deposits around the world.”
The research was published in the Journal of Geophysical Research: Biogeosciences.