Every year we are visited at work by swallows. They seem to like using the unit to make nests for their offspring and we certainly enjoy a noisy few summer months. They are beautiful and impressive birds to watch at close hand, although are not very helpful when it comes to trying to take pictures of them!
The one downside to having these visitors every year is their tendency to poo down from above without mercy... There is absolutely nothing I can do to prevent this and it's a continual job clearing up the splats!
I will sometimes cover up stuff that I really don't want splattered, and as you can see from the final picture below the swallows are highly accurate and intensive in their poo bombardment! :o)