Researchers discovered a source of data on past fires in bat guano.

Studying animal feces can sometimes reveal unexpected details about their lives. For instance, in one past study, the analysis of guano samples helped identify surprising dietary preferences of the bat species Trachops cirrhosus. It turned out that they fed not only on frogs and lizards but also on hummingbirds and even other bats.

Now, scientists have demonstrated that the naturally decomposed remnants of bat droppings can also reliably reconstruct the history of fires in a specific area. An article on this recently appeared in the journal Geophysical Research Letters.

Samples of guano from two species of the night bat genus—Myotis grisescens and Myotis sodalis (gray and Indiana bats)—were collected in the limestone cave Cripps Mill (Cripps Mill Cave) in Tennessee. This location serves as a nursery for bats during the summer. The fecal samples were then analyzed using radiocarbon dating methods and the charcoal content was measured.

As a result, scientists obtained dated data on environmental changes in the vicinity of the cave. According to researchers, bats became unwitting chroniclers of fires due to their behavioral traits. While hunting for insects during the warm months, charcoal from nearby fires could settle on their fur. The charcoal particles would then end up in the bats' stomachs (as they groom themselves by licking their fur) and on the feces-covered cave floor.

In this way, the guano layer “captured” the surrounding fire activity. This “picture” was compared with data on fires within a 200-kilometer radius of the cave, taking into account the presumed hunting territory of the bats and the distance over which charcoal particles could spread from nearby fires.

Ultimately, a significant correlation was found between the charcoal content in bat droppings and the total area of burned land during the non-winter months, as well as controlled burns during this time, with each centimeter of guano layer “reflecting” the history over a six-month period. The connection with year-round data and the period when bats typically enter hibernation, on the other hand, turned out to be weak.

The researchers suggested that bats are attracted to recently burned areas for hunting and feeding, as these attract certain insects. At the same time, in areas affected by forest fires, potential prey is absent due to smoke and heat, which likely leads bats to avoid these regions.

In conclusion, the authors of the new scientific study noted that the charcoal preserved in bat guano is a reliable source of data, a kind of “paleo-fire archive” that can assist researchers in distinguishing between controlled burns and unplanned wildfires.