Carol, I do firmly believe in doing all we can to protect our blues from aggressive competitors that may harm them or their babies. But when it comes to favoring one native songbird over another – either within a species, or of a different species (with the possible exception of HOWR, who are very destructive) – I tend to let the birds sort it out themselves. I usually have at least a couple pair of TRES and one Bluebird pair, and sometimes a BCCH pair all vying for my four nestboxes every year – I call it the “Nestbox Wars”. Eventually everybody settles down and finds their own place without any tragedies (although NOT without quite a bit of drama!) It’s the HOSP and the HOWR that really get on my nerves. HOSP are easier to deal with. HOWR take uber-vigilance and clearing the nestbox of sticks used in their dummy nests (sometimes multiple times in a day). It can be exhausting!