I know that bluebirds come back and start looking at nest boxes as early as February. I love bluebirds. The color of this bird is pure joy. They are known as the blue bird of happiness. This works for me, they do make me very happy. In my blue-birding days, I had a total of 50 bluebird boxes up around the country side. I started making them in the early 90's. I also knew to monitor these boxes weekly. I had notebooks of things to check, nesting material indicated the type of bird trying to build a nest. Bluebirds and tree swallows will share the same type of box, you might also have chickadee's, wrens, or the dreaded English sparrow! Those had to be removed.......... English sparrows can nest anywhere, bluebirds and tree swallows have lost their usual habitat because of wooden fence posts not being used any longer. They seemed to struggle at changing their instinctual nesting sites to another version, until we helped by building boxes. I would also count the eggs and the date they would hatch and the day they fledged. Each of my boxes were given a name of a female friend in my life. I felt numbers were too impersonal and women being the Nester's, deserved nesting box names. I would ride my three-wheeler around our fields and our neighbors fields checking and repairing boxes into late summer. Successful bluebirds could have 3 nests a summer, fledgling 3 to 4 babies at each nesting.
I'd like to say the Bluebirds flourished, there were some good years..... but often I would find dead bluebirds in a box with sparrow nesting material built over it when they came in behind the bluebird and killed it for the box. This always saddened me. I could pull out a sparrow nest one week and come back to see another newly built nest and 5 eggs laid in a weeks time! They are aggressive and proficient, finally the female would leave the box, the male would try to attract another mate and it would begin again.
Three springs ago we had early warm weather and the bluebirds began choosing boxes for their nest. A sudden ice storm and a two week freeze took the lives of many bluebirds. They couldn't keep warm and couldn't hunt insects during that freezing spring. The numbers of bluebirds in all of Ohio and states east, south and west were also effected. We were back to numbers of bluebirds in the 80's...... a major backwards step. I have had a couple pair coming back now, joyfully I had one nest fledged 2 baby bluebirds. The tree swallows have never returned here. I no longer monitor boxes, the greed of farmers tilling so close to the fences mean I can no longer get to the boxes. Some of the fences that had boxes are gone and many of the boxes are old and falling apart. I leave the project to the next generation and hopefully they well step up......... they haven't yet.
I have learned that nature takes it's own course, with or without our help. I do rejoice when I see bluebirds in my yard. I always say a little prayer for them, hoping they will adjust and thrive so my grand children know the blue birds of happiness too.