restricting starlings but not PM's. the first hole designed around a PM with NO pressure on the breast or back. They go through these holes as if they were round. Actually the areas to the right and left are for Babies to be able to peak out. The first design I used last year was the exact size of a PM and didn't have the open area to the left or right. Had two compartments fledged 7 Babies with them
As you can see from the photo they are blocked at the hips. I have found starlings are almost the exact size of PM except for the hips. PM IMO have narrow body but their giant wings have to slide through also. This IMO is where Current design SPEH's lacks. The small opening required the PM to rotate his breast bone. IMO this is why it takes them several attempts to get in them. My holes lacks this narrowing at the center and still can restrict starlings. Notice I didn't say "prevents". and I got 5 more designs I'm still testing.
I'll let you work on the sparrow's This is about to drive me over the wall. I still got to research and study them for atleast two more years before I can totally reveal this entry hole, Plus I got about 5 more I'm working on. Exact size is still not determined due to the small differences in Starlings and PMs sizes. IMO they don't all conform exactly.
This is about to drive me over the wall. 