Bat guano beats burgers for blind salamanders
For cave-dwelling salamanders, bat droppings are part of a balanced diet.
A species of blind, cave-dwelling salamander in the US mid-west has switched from a normal carnivorous diet to eating nutritious bat guano, say subterranean researchers.
Because bats don't digest their food properly, weight for weight their droppings contain more protein and nutrients than a Big Mac. This makes them a perfect snack in a pitch-black environment where food can be scarce.
University of Oklahoma, US.
But when Danté Fenolio, a salamander expert from the University of Oklahoma in Norman, led researchers into January-Stansbury Cave in northeastern Oklahoma to study its population of grotto salamanders (Eurycea spelaeus) they got a surprise. It seems these salamanders decided to cut out the middle man, heading straight for the guano itself. Some fish have been found to do this before, but never amphibians.
They made the discovery after some unpleasant experiences with young salamanders spitting up bat guano on them. "It's not uncommon for salamanders to regurgitate on capture," explains Fenolio. But it is unusual for what they produce to be full of black droppings. The team also saw adult salamanders feeding on the guano, which piles up to two metres deep on the banks of the cave's underground river.
Around 15,000 grey bats (Myotis grisescens) breed in the cave during the summer, and it seems that the blind, colourless salamander has turned to the plentiful food source they excrete. The researchers tested the muscles of the salamanders and found that their carbon and nitrogen isotopes matched that of guano, indicating that guano was a significant part of their diet.
The researchers also analysed the guano for nutritional content and found it to be surprisingly good: it is very similar to the crustaceans that salamanders otherwise eat, with a protein and mineral content that beats a burger. They report their findings in Proceedings of the Royal Society B1.
"If you could somehow sterilize bat guano, it would probably make a good human food source," says Fenolio.
William Elliott, a cave biologist with the Missouri Department of Conservation, says it's not surprising that the cramped, guano-filled caves of the region still hold secrets. "They are kind of unpleasant to crawl into," he says, "so we haven't really observed much of what happens in there."
But Elliot says it's important that we do, to find out how endangered species like the grey bat support delicate cave animal communities. "Finding the links in these ecosystems will help us to conserve them," he says.
- Fenolio D., et al. Proc. R. Soc. Lond. B , Doi:10.1098/rspb.2005.3341 (2005).