Holy Guano Batman!
My 50 lbs. of Pigeon Poop on the balcony has nothing on this!
I read an Associated Press article today. Since I can't reproduce it without risking loosing my house I'll give you the story in my own words.
A couple from upstate New York bought a house last summer that had a few bats in the attic. They delayed getting them removed due to the fact that baby bats can't fly and the time wasn't right to have them removed. By January the smell was permeating their nostrils so they checked out the attic where they found loads of dead bats and 3,500 Lbs. of Bat Guano! Turns out that the attic was housing hundreds of bats. It cost them $25,000 to have it removed. That's $7.15 a pound! I never thought bat guano could cost more than prime rib!