Can my roommate file a lawsuit against me?

First, this is not "legal advice" and is not subject to attorney/client privilge. Having said that, I have the following thoughts.

The fact that your roommate was doing something "against the rules" is a separate issue from you letting the bird out the window. The old addage of two wrongs don't make a right applies here. So, lets forget about the dorm rule of no pets. Your action was to inentionally damage the property of another. I don't know what state you are in, but in most states there is an action for "conversion" - which doesn't strictly apply here because you did not "convert his property to your own use." However, one may argue that you did so ... and your use was to get rid of his property. Your act was "intentional", so it is not likely to be covered by insurance. Think about it, is this really any different then if you got into a fight with your roommate and put your foot through is television or computer screen? In either event, you damaged his property. Can he sue you? I suppose, probably in small claims court ... again depending on what state you are in. Most states have a specific dollar amount ... anything at or below that dollar amount goes to small claims court. My guess is, uless the bird was some rare species, you would likely be in small claims court.

At the end of the day, your actions were immature and foolish. To me, it is exactly the same as breaking his computer because you were mad. My suggestion is that you work something out with your roommate to help replace the bird and that you grow up.