Do birds like certain hole sizes? This is what I've discovered in my yard.
Most of the houses I make have an entrance somewhere between 1¼ and 1⅜ inches, depending on what I'm building it for. Those smaller openings are intended for birds like chickadees, titmice, and wrens. For bluebirds, I use 1½ inches.
I also learned that making the opening bigger isn't necessarily better. A larger hole can let birds like starlings get inside and take over a house meant for something smaller.
So, a properly sized opening gives the smaller cavity-nesting birds a better chance of having the house to themselves.
Around here, I've watched birds land at an entrance, look inside, and then fly off. Sometimes another bird will come along and go right in. I can't always tell why one bird passes up a house and another seems perfectly happy with it, but the entrance hole is one of the things that can make a difference.
So far this has worked for me.
For something that takes less than a minute to drill, that little hole ends up making a lot of difference in which birds can use the house.
And I don't get much say in that.
A Note on Sizes
Entrance-hole recommendations vary by species. I use the sizes described here based on what I build and the birds around my yard. For species-specific nest-box dimensions and recommendations, Cornell Lab's NestWatch is a good resource.