Hello,

I have a setup of two bluebird nest boxes, spaced about 10 feet apart in an attempt to reduce early competition with Tree Swallows. In Box #1, we are about 22 days from first bluebird egg laid. All five eggs have since hatched and babies are about 5 days old.

Box #2 had some house sparrow activity in early May, but I removed the just started HOSP nest and moved Box #2 closer to Box #1. I had not seen the HOSP around since, until a few days ago.

While Box #1 eggs were being laid and incubated, I observed the male bluebird guarding both boxes. I also saw papa bluebird go into the empty Box #2, but the box remained completely empty. A few days ago, I noticed more Tree Swallows around. I checked Box #2 but still empty, until yesterday when I opened the box there was a tree swallow egg inside, but no nest! Even more interesting, about 10 feet away, I observed a male and female tree swallow pair mating. This morning I observed the TRES entering Box #2 a few times, while all seems normal at Box #1 (male feeding and removing fecal sacs).

Would a TRES lay an egg in an empty box (no nest)? If not, could it be that some other bird removed the nest but an egg was left behind? I looked around but did not see anything that looked like a nest around on the ground. I'm really not sure what happened here...could a TRES build a nest and lay an egg in one day?