What the heck, I'll take a shot at this.
Picture a normal opened umbrella. Now picture the umbrella after it has been broken and deformed by a strong wind. It's ribs (for lack of a better word) are bent and twisted, the fabric may be torn, there will be bits of umbrella sticking out at odd angles, etc.
This sentence is saying that the bats look like they are in the same condition as the umbrellas.
Note that it doesn't necessarily mean that the bats have actually been hurt (although they could have been).