I remember scrub jays doing similar things in my childhood yard in Eugene in the 80's. We had a chicken yard and scrub jays would sometimes grab baby chicks and carry them off. One such memory was of an ambush where the jay waited for the chick to walk by its hiding spot and they jay flew out and grabbed it; much like a cat would prey upon birds.

Corvids certainly are resourceful.

Scott Downes
downess at charter.net
Yakima WA