Move in day at Tree Swallow University

Last Wednesday a few Tree Swallows flewover. Friday they were buzzing around the river. Today they were sitting on boxes and one of them had a bird already moved in. 

Life is not so tranquil though; lots of aerial fights, which I assume are males fighting over... now that's an interesting question. Do they fight over females or boxes and females are incidental? 

There are seven boxes from the Martz bus depot on Pickering Street to Riverside and Ross. Five of these had tree swallows zinging around them and one (in the woods) had a Tufted Titmouse couple setting up.