I just got my first set of chicks on Tuesday - 8 baby Buffs. They're all looking great except for one which has the following condition below. This looks like it's right on her rear. What am I looking at? My wife and I have taken a warm wash cloth to it with no avail. It's quite hard and the little girl chirps her lungs out when we wipe. What is it and what course of action should I be taking?
Full size pick is at: http://www.gnomesathome.com/chick.jpg
Thanks for your help!

Full size pick is at: http://www.gnomesathome.com/chick.jpg
Thanks for your help!