To those who mentioned owls and other type deterrents I know first hand that they do not work long term. This kind of situation requires something different. I did some research and found that the most effective solution to stop birds from roosting was spikes. You can buy strips of them in plastic (cheap) or stainless steel. They are generally cross angled and I'm sure do a good job but they are meant to install on surfaces that are completely open. The spikes are typically 4 inches long or more and would not fit on top of my doors without being trimmed. Additionally, the doors would have to be removed from the track, at least partially, to install these 1 foot strips. But the spikes gave me an idea that I hope will solve my problem. There is about a 1 inch gap between the top of my doors and the bottom of the header (see the pictures). And the space in there is about 2 1/2 inches high by about 4 inches wide, so birds have plenty of room to roost but their tail, and butt, point inside. Someone in this thread mentioned that their sheet metal shroud covering the track is bent down very close so birds cannot get underneath it. However, my shroud is held in place by preformed clips so I cannot just bend my shroud down. I had some left over aluminum trim stock so I figured out a design that would take up that space and, hopefully, solve my problem. The aluminum trim stock is easy to cut (just score with a utility blade and bend), easy to bend with clamping wood on it, and will never rust or corrode. And I installed it from the inside without having to mess with taking the doors off. The short pieces at the end of each door were only 10 inches wide and easy to make. The center section of the doors, between hangers, was 58 inches so I decided to make 2 pieces to cover that length which was much easier to deal with. My trim pieces were 9 inches wide to start, then bent almost in half (one side 1/2 inch longer) and then rebent to form the appropriate angles as shown. Hopefully, this will give all of you with the same problem some ideas and make something like this work for you. For those of you who temporarily hijacked this thread - thanks for all the interesting swallow information. ;-)