Better get a few Bolivian Tree Lizards
Then when they do the job you'll just have to release wave after wave of Chinese Needle snakes. That'll wipe out the Lizards!
Then you'll just have to find the gorilla that thrives on those snakes. But don't worry about the gorillas as when Winter rolls around they'll simply freeze to death.
So you better not seal up your roof at all.
Oh and I had a couple pigeons lay eggs on my balcony a couple years ago. Since I was moving anyway I didn't really do anything about it. But, after they flew away the adults came back and laid more eggs, so they can be a constant problem even if you only get rid of the ones in your attic.
I actually heard that tying up CD's to strings helps keep them away (they are scared of the reflection of the sun or something), so maybe keep that in mind once these ones are gone.