Hello Windmillman,

It takes about 2 weeks after the last egg is laid for them to hatch and another 18-21 days for the young birds to leave the nest.

All of my boxes are made of cedar and I never have problems attracting bluebirds/tree swallows and sometimes chickadees.

I think the placement of the nestboxes is more of a factor than the nestbox itself. Location, location, location. Where do you have yours?

I have three boxes in a remote location that is lightly wooded and grass is mowed occasionally. I could never get blues here in town where I live so I made arrangements to place them at another location last year and had one nesting and now in the second brood for this year. I have three boxes placed 120 and 150 feet apart in what seems to be a good location but started worrying about material because the birds have only used the one made of pine. I put up another box today at 90 feet from the closest bluebird box but it is 210 feet from the active box.

Well Bluebirds have a territory of 300 feet, they won't let another bluebird nest any closer than that, normally there are exception though such as if the boxes are not in sight of each other. So if your boxes are closer than that you won't have another set of bluebirds. You could get Tree Swallows though or Dees. Mowed grass is better for bluebirds to find food but I always have some nesting in a box that isn't near mowed grass.

OK What I thought I had learned was to place the boxes 100 feet apart which would be 100 foot range for each box. If they need 300 feet I can only get one nest of bluebirds since I only have 600 feet available to me and my active box is approximately in center. Hopefully other compatible birds will use the other boxes.

windmillman....you probably confused 100 yds with 100 feet. Bluebirds territories are typically 100yds or 300 feet. There are cases where the boxes are closer but not within sight of each other where they do nest closer but it isn't the norm. You could get Tree Swallows nesting with the Blues though. Good luck!

Yep you nailed me on that.. I read 100 yards but thought 100 feet. Math and geometry were my strong subjects when I was a school boy but that was a long time ago. Thanks for correcting that for me.
I'm going to need to find more locations. The problem is finding locations with free access but very little public traffic. The folks at the state park allowed me to install houses out there but being a public place, it was not long before I fell victim to vandalism. I've never understood why someone takes pleasure in being destructive but it only takes one bad apple to mess things up..

Will it encourage Tree Swallows if i move one of the boxes closer to the active Bluebird nest?

I wouldn't move it any closer. As long as they are in the open enough Tree Swallows will find them. They are fun birds to have around too. I have some boxes paired and can get Blues and Tree Swallows nesting about 25-30 feet apart but not any closer than that. Sorry you had a problem with vandalism...I worry about that too with some boxes that I have at a park near us.