Mystery Chick Deaths on Kings Highway

I didn't get out to check the boxes yesterday, so I looked at them today.  I expected to see empty boxes.  Wrong.  I found a mystery.  All the chicks were healthy on Monday.  Not so today.

As I got out of my car, I saw the flies and picked up on the familiar odor.  Still, I did not expect to find 2 dead chicks in the box near Stai Coulee.  Two live chicks remained.  One looked weak.  Whazzup?

I waited and watched.

The 2 live chicks, called.  Their mom appeared and flew around the box.  When she seemed hesitant to go inside, we drove off.

No sign of trauma.  Maybe the male died and they starved?  Maybe it had something to do with what's in the bugs?

Maxville Box 1.1:  3 very large chicks.
Maxville Box 1.2:  empty

Kings Hwy Peterson Box:  new bluebird nest, female in the box, 1 bluebird egg
Stai Coulee:  2 dead chix (I removed them); 2 live chicks (one appeared weak); female hanging around.