More than one Swallow; it must be Summer

Over the last few days we've noticed small birds in the Swallow/Martin family around our apartment complex, and today we got a closer look at three individuals swooping around, who appeared to either be nesting in, or gathering nesting material from, the dryer vents that decorate the apartment blocks' exterior walls.

These vents take the warm damp air from the tumble dryers, and vent it to the exterior, taking a certain amount of fine lint with it, and dumping the grey lint on the flowerbeds beneath. The vents do look very like British  House Martin nests,  though here in the Pacific Northwest the species I am seeling is probably Purple Martin or a Tree Swallow.

I'm looking forward to having a quiet garden to attract the birds so I can get a better look, and start learning some of the species I am seeing.