A 4,300-year History of Dietary Changes in a Bat Roost Determined From a Tropical Guano Deposit

Bats provide numerous ecosystem services as they pollinate, disperse seeds, and reduce insect populations. It is thus vital to monitor and understand their foraging habits. We analyzed sterols and stanols in a rare discovery of a similar to 4,300-year-old bat guano deposit from a Jamaican cave to infer relative changes in bat feeding guilds over four millennia. In this deposit, zoosterols and phytosterols, in conjunction with delta C-13 and C/N data, revealed two periods of increased frugivory relative to insectivory from ca. 1000-500 BCE and ca. 700-1900 CE. We propose two possible explanations for these intervals of increased frugivory relative to insectivory. (1) Previous paleoclimate data suggested these intervals were warmer and drier in the region, which we hypothesize resulted in reduced insect availability. We supported these inferences by comparing the same analytes in fresh guano from frugivorous, insectivorous, and sanguinivorous (blood-drinking) bats, which showed that bats with animal-based diets produced guano with lower C/N ratios and higher cholesterol/(cholesterol + sitosterol) ratios than those with fruit-based diets. (2) The change in the chemical composition of the bat guano during these two periods may also be the result of a shift in the relative species composition of the bat roost that is a greater proportion of frugivorous relative to insectivorous bats during these two periods. This novel, non-invasive method, based on the chemical composition of bat guano, tracked changes in tropical bat foraging habits extending back in time over four millennia.

Automated summary

The study used the chemical composition of ancient bat guano deposits to track changes in bat foraging habits over the past four millennia, revealing two periods of increased frugivory relative to insectivory.