Guano, it seems, is a rather nutritious, protein-rich substance because bats don’t completely digest their food (mostly insects in this case). The January-Stansbury Cave in northeastern Oklahoma is a summer roost for about 15,000 endangered gray myotis, and these bats, through their droppings, support an unusual and healthy subterranean ecosystem.

The discovery was described by Danté Fenolio, of the University of Oklahoma in Norman, in United Kingdom’s Proceedings of the Royal Society and reported online by news@nature.com.

Fenolio led a research team into the cave to study its population of grotto salamanders, a blind, colorless and carnivorous species. They got a surprise when the salamanders regurgitated, as they often do when handled. What they spit up was clearly bat droppings. The report said they also saw salamanders feeding on the guano piles in the cave.

Some fish are known to eat the droppings of other species, but no amphibians are known to do so. The salamanders in this cave apparently learned to tap what proved to be a rich and easily obtained food source.

The researchers analyzed the guano for nutritional content and found it to be surprisingly good: similar to the crustaceans that other salamanders eat, “with a protein and mineral content that beats a hamburger,” news@nature.com said.