Tree Swallows (Tachycineta bicolor) are very competitive and will compete for bird boxes. They will mark-out their territories and compete with the Bluebirds to move into unused bird boxes.

Videos: Tree Swallow

Listen to  Tree Swallow:

Time Stamp      Bird Song
0:02:06            Great-horned Owl
0:02:45             Sora
0:04:36            American Robin
0:04:49            Swainson’s thrush
0:10:58            Tree Swallow
0:12:36             Swainson’s thrush