Has anybody had refusals with this opening? I have birds here but they seem reluctant . Seema like the new houses have a better opening.

I've only ever seen round entrances around here. What's the idea of a slot?

I know people here that have them and have not had any trouble.
Idea of the slot is to prevent starlings from entering the hole. I use the crescent shape on my houses and before I installed them and had just the round hole I had starlings kill adult purple martins inside the house.

I see.

Daggum sparrows still get in though..

Old timer here had martin houses, he'd camp out in his shed with a pellet gun for the squatters, lol. Friend uses both the houses and the gourds, the gourds work better, his has the round holes. Never saw starlings at his setups, but gets an occasional tree swallow camping out.
Had him set a bluebird house away from the Martin complex and that cleared them out.

Busy time of the year here. Starlings and house sparrows have been in the crosshairs for the last week. I have not seen the modified holes and will let my landowners know about them. I spend alot of time with the shotgun and pellet gun on a handfull of farms and a few homeowners working over the invasive population.

That was my first paying gig as a NWCO before I ever knew what a NWCO was. The neighbor would pay me a dime for every starling or sparrow I shot off his gourds.

Starlings are longer legged and its to much of a stoop for them to bend over and get in the slot or cresent.

My martin house has the same crescent holes and it works to keep the starlings out. Never understood why until Warrior explained the reason. Good thing to know. Thanks!