Tree swallow

People always surprise me - when they built the new elementary school near the track, the landscaping seemed like an afterthought and many trees that were obviously meant for the perimeter died in their wraps because no one bothered to plant them - but this year 5 nest boxes have been added on the border of the field. I don't know if the swallows are nesting in them, but they sure like sitting on them to rest between bouts of swooping and diving.
I'm not sure if there are always this many barn and tree swallows around and I am just more inclined to see them or if there really are more this year - they seem to be everywhere.

[any theories, H?]