Are these chickadees making a poor decision? [Update: Happy ending]

I'm enjoying the politics of nest box possession down at the Charles River Peninsula this spring. Parties include the house sparrows (at least two boxes claimed--not a good sign for next year...); the bluebirds (at least two boxes actively protected); and the tree swallows (all the rest). And today, it looks like a pair of chickadees think they have a shot at a box. Are they out of their minds?

Some context: Yesterday there was an eruption of what appeared to be mayflies--I had to close my mouth walking through the meadow, but the tree swallows were in heaven. This afternoon no mayflies and few tree swallows--they must have found more productive foraging somewhere else on this chilly wet day. Which means the chickadees could take a chance at a nest box while the tree swallows were away.

So here they are, working as a team. One would enter the box while the other stayed in the brush as a look-out. They would take turns, occasionally greeting each other with a beak tap (or ritual feeding--I couldn't see it well). What were they doing? Not putting things into the nest box--taking things out. (Apparently chickadees demand a clean space before adding their signature moss nest lining). I expect an angry pair of tree swallows this evening.

I would approach the nest box until they noticed me, "chickadee-deed," and flew off. Then I would pretend to leave--move off and then come back. The first few times this worked. The last time they seemed to get wise. Instead of returning to the box when I left, they followed me--both of them--"chickadee-deeing" all the while. Only when I was a significant distance away did they fly back and start their activity again.

At any rate, I'll keep checking on them. I can't imagine they'll be successful in the end. With the tree swallows (who are themselves competing five or six at a time for each box) and the increasing house sparrow pressure, I can't see how they can last. But who knows? Maybe these chickadees know what they're doing...

[4/29 UPDATE: I know nothing. Day three, the chickadees are still at it. Clearly I overestimated the ire of the tree swallows. In fact, I don't know what's going on with the tree swallows--today the bluebirds were moving between four different nest boxes, unchallenged. Also, the flies were back today and are definitely NOT mayflies (see next post).]

[4/30 UPDATE: Warm weather returns. Tree swallows become aggressive again. Chickadees nowhere to be seen. Yellow warblers and orchard orioles singing]

[5/1 UPDATE: Chickadees are back waiting for the tree swallow to leave. Tree swallow is aggressively defending nest box--FROM ME! Perfect circles around me three times.]

[5/15 UPDATE: Unbeknown to me, the chickadees found a different box around the corner (less desirable to tree swallows) and now appear to have chicks. Check out the photos below. I'm pretty sure that's a fecal sac in the chickadee's beak.]