The sickness disturbs bats' sleeping and hibernation habits. Instead of resting, they go out and hunt—but often at times where there aren't many bugs to be had. The fat reserves they had stored up to help them hibernate get used up. Eventually they just tucker themselves out and starve to death. It's called "White Nose Syndrome" because of a white fungus that appears on the bats' muzzles as well as their wings. So far it's unknown if the fungus is what makes them ill, or if it sets in after the bat is already sick.
An alumna from my high school (who I know by name but that's about it) is conducting a study about the social calls of bats. Their social calls—defensive territory marking, distress signals, calls from mothers to pups—are different from their sonar calls, and not as well documented. The more we can learn about bats—including how they talk to each other—the better equipped we are to help save them. If you've got a spare $10, chip in so Ms. Brokaw can reach her $3000 goal. The link is below.
Bat Speak: What Bats Say and Why We Should Listen
The little brown bat (myotis lucifugus), the species hit hardest by WNS.