I've noticed birds love making nests in dryer vent and other pipes.

There isn't always a store bought solution to this and many times the ones that come with the pipes originally get broken.

This video shows you an easy way to put a critter screen on your pipes. If it's a dryer vent pipe you may have to remove it periodically to clean out the fluff that gets caught on the screen.

Whatch the video to see how it is done.