actually I think the big ones are birds nests, can't think of what kind though, in the second picture, you can see a real mud dobber nest in the middle
finished my research. It's actually a Cliff Swallow, found mainly in the western US, but has started to spread east with the abundance of nesting sites. They are now using the underside of bridges, overpasses and elevators. the female will lay 3-6 eggs, and when the nest gets full, she'll move the eggs to another nest in the colony.