This diagram shows the dimensions of a starling resistant entrance hole (SREH). This entrance hole will exclude most starlings (and all Screech Owls.) The height dimension (1 & 3/16") is extremely critical. If made a hair too big, starlings will get in; if made a hair too small, martins won't be able to. Also, the hole placement is very important; the bottom of the entrance hole should be no more than 1/2" above the porch, and is most effective in excluding starlings when placed flush with the porch and compartment floor. This hole will also work on gourds, both natural and plastic, as well as aluminum houses. When cutting this hole in wood houses or plastic/natural gourds, use a jigsaw, and cut it slightly small, then file or sand it to the proper height. People with aluminum houses can modify the doors themselves. People with Trio brand aluminum houses can purchase replacement doors with the crescent SREH's already cut in them by going to our online catalog. (and clicking on Starling Resistant Entrance Holes). Photo #2: Wooden T-14 doors modified using jigsaw and Seekamp adjustable SREH plates Photo #3: Trio aluminum door modified with Seekamp adjustable plate Photo #4: Preparing to cut SREH in natural gourd.