Not sure that's a correct assessment of foxes, Sylvia. I have known them get into a pheasant pen and kill every poult, and only eat a few.
I agree with jaykay. I don't believe foxes are malicious. Faced with a huge banquet, he'll kill all, eat as much as he can then carry the rest away for later. It's jsut that he doesn't get time to take them away. We lost a number of hens in one attack years ago and that's what we found happened. We found bodies stashed on the waste ground by our house. Faced with captive prey, he's hardly going to take one, and hope the rest will still be there tomorrow.
I'm afraid the onus is on us to protect our birds - no point railing against nature.
Sorry about your birds, though, clydesdaleclopper.