I had a problem last year with a few grey back crows that were constantly attacking my birds around the loft. Haven't seen them about yet this year but then again my birds haven't been out much either.
Our 1st race is on the 12th of April and I'll be ready once I start letting the birds out of the loft in a more regular basis as they are still confined most days.
I'd leave the birds and race them to the loft they are in and move them over to the new loft when racing has finished. Plenty of time during the end of season to settle them to the new one