I’m assuming they keep out mockers. I think it worked for me but I only had a mocker for a few weeks and can’t remember. Anyone have experience. I, recommending it to a person with mocker issues.
If the openings are 1.5 inches it will keep out mockingbirds. That company also make the feeders with 2 in openings. The reason I know I purchased a feeder last week. Another lady wanted a different color and that one had 2 inch openings. She called the garden center back and said the mockingbird went right in.