Well done mate, I dont know if you know, but crows are scientifically regarded as being the most intelligent animal after man!.....mmm
I do most of my shooting of crows with shotgun and .17hmr, but something else that works for me, is a bit of fur (from the hood of the old parkas, but it could just be a bit of rolled up rabbit skin) on a long length of fishing line. When any crows start coming into your decoys, give it a few tugs, (the fishing line, lol) and the crows usually go mad and sit on the nearest dry stone wall. Dont know how it will work for an airgun. Good luck. Failing that, an ol