We've been having huge problems with crows too. They take all the poultry food, have just moved onto eggs as well as pulling out all my baby sweetcorn and pumpkins, courgettes, gourds etc. (literally every single one - planted inside the chicken enclosure, inside another fence to keep the chickens out). We had somebody round to try and shoot them twice and he got a handful which were duly strung up - they took no notice. They also ignore the various bird scaring devices except to peck out the eyes of the smallest scare crow (interesting psychology!). Our latest trial which is certainly slowing them down a bit is to string fishing line across the top of the run. We have a huge run (40m x 70m) so there are big gaps in between that they can get in through but they can't see the line very well so they don't know where to go. I think we need a bit more up there but at least one bird has hit the line so far (and broken it - you need stronger than 12lb!) and at the moment they're all hanging round the edge of the run trying to work out what to do next! It doesn't hurt them but scares them enough to think twice and hopefully go for a safer meal elsewhere. Will keep you posted whether it continues to work or whether we have to find another approach!
H