County Durham,
United Kingdom 
Hya having a problem with Cabbage Plants they keep getting eaten away, Bought some more, sprayed both sides the next day there was hardly anything left, never know this before, I tried using collars but made no difference, cannot find any signs of slugs or anything similar,can you give some advice to what's causing this problem, Thanking you
24 May, 2019
Answers
pigeons are a strong culprit too. I have had them strip plants in a couple of hours.
24 May, 2019
Yes, the good old Wood Pigeon would be my main contender for the damage. I would suggest that netting would be the answer. Collars would be a prevention against the Cabbage Root Fly but you would still expect to find the dead plant which isn't the case.
24 May, 2019
Providing some water & a cheap alternative food source for pigeons & other critters might help too. I'm in Manchester & it's been surprisingly dry lately in the NW?
24 May, 2019
If the bites are kind of squarish, it is likely to be rabbits or hares, or the like--rats occasionally do that here in Phoenix. If the bites are triangular, then birds may be the culprit.
24 May, 2019