I live on the Oregon Coast, and have detected a flying squirrel on a backyard game camera. I’d love to support them. Reading about them, it appears nesting habitat for raising young is in short supply, and that this can be bolstered with nest boxes. Has anyone tested out the various nest boxes? Interested to see if anyone has a favorite. Right now, I’m leaning towards the “Texas” design.
I think it depends on the species and could even vary by location within a species.
I am in NC - and low elevation. We have the Southern flying squirrel and these readily use any bird box.
I typically use a standard design for eastern bluebird which has an entrance hole or 1 1/4 inch. Might be 1 1/2.
I also modify some to have an entrance hole or 1 1/8” - this excludes larger birds which allows chickadees and brown-headed nuthatches to nest in peace.
But - my boxes with either entrance hole size admit the flying squirrel. I have a dozen boxes out and always have a couple occupied by flying squirrels.
Given your location you probably have a larger species. We also have Northern flying squirrels here but only very high elevations. My colleague uses boxes for them - the differences I remember from years ago are: the cavity entrance is at an upper corner and was squared; there is screening used for the floor of a small mesh size like about 1/8”.
I imagine some studies have been done but I am a bird person in my day job ha - so I don’t know.