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.
Fungi,
bacteria and crustaceans are all known to feed on guano. These
creatures in turn were thought to provide the food for carnivores such
as salamanders.
If you could somehow sterilise bat guano, it would probably make a good human food item.
Danté Fenolio 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.
Bat burgers
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.
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"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.
If you could somehow sterilise bat guano, it would probably make a good human food item. 
