I can’t definitively swear that it works. But I haven’t seen any new evidence of bird kills. After she killed three Lesser Goldens in one day, I had to do something or I was going to do something drastic.
I take the collar off at night and, after removing accumulated hair every morning from the fabric, put it back on her before she can go outside. After crooning, and praising her for wearing it for a couple days, she now submits to my putting it on her. After making sure the length of the break away collar is flat, not twisted inside the fabric, I approach from behind and below her eyes. The break away collar is hard to snap together, but it seems to work the way it was designed .