White onion set gone missing after planted

by JR
(West Midalnds)

I have planted white onion set in garden caged by string to stop cats & birds but 2 days ago when checking plot several of the onions were missing no signs of digging or burrowing nor any kind of pecking marks just looks as if I have picked them straight out of the ground just left with perfect round hole they were in, looked again today a few more gone help!