By my records, I have trapped and dispatched 42 European starlings and 94 house sparrows since I got my sparrow trap last October. I love this trap because it attracts the non-natives and gives me the opportunity to kill them humanely without harming the native species in any way. The occasional Dark-Eyed Junco, House Finch or Tree Sparrow gets trapped but I can easily release them unharmed--and it's a great opportunity to see the native species up close.
Here's a photo from the seller's website showing a sparrow trap full of quarry:
I haven't killed all the starlings I've trapped. I have clipped the primaries on a dozen of them and released them during particularly harsh winter weather to give the raptors an easy meal. Apparently, it worked (see photo at bottom). I've found two dead starlings with clipped wings in the windbreak, both headless. My first thought upon finding them was that the screech owls caught them and only had the heads for a meal. I've read that, in good times, Saw-Whet owls will eat only the heads of mice, but I seriously doubt there are any Saw-Whets here. I hope other birders with more experience than me will chime in and offer their opinions.
To the uninitiated this practice of trapping invasives and killing them probably seems harsh. But it's a bird eat bird world out there and I feel that I'm helping the local cavity nesters by eliminating as much of their competition as I can. I cringe at the thought of finding starlings nesting in one of my owl or duck boxes! I read an article about managing bluebird trails that simply stated it is irresponsible on the part of the bluebird landlord to place nest boxes for them and not monitor them to prevent competition from non-natives. Trapping is legal since invasive species are not protected under federal laws and in some areas it is encouraged by wildlife authorities.