by meb » Mon Mar 15, 2010 2:38 pm
Bluebirds start showing up in March. Cavity nesting birds zero in on black holes, so bluebirds WILL investigate your gourds, unless you keep the holes covered until they have settled into some other housing.
In my area, Tree Swallows arrive a week or so before the Purple Martins, and they, too, will try to claim your gourds, and will chase Purple Martins away.
Your best course of action would be to install two bluebird houses nearby WELL BEFORE the PMs get here - one for a pair of Bluebirds and the second for a pair of Tree Swallows. Once they have claimed the houses, they will leave your gourds alone and will chase away all other Tree Swallows and Bluebirds.
Tony mentions in his reply above that Tree Swallows seem to nest at the same time as sub-adult PMs, but they often claim a cavity early and then dawdle a long time before actually building their nest.
I believe Keith Radel will offer some good advice about Bluebird housing; however, Purple Martins are not a priority with him, so if you don't find other PM landlords in your area, post your questions on this web board, and we will all help you as best we can.
I didn't even mention House Sparrows and Starlings - big problems for some PM landlords. I'm sure you've read about them already!
Peggy in Chisago County