hmm this was discussed elsewhere recently ... one problem is that the 'additional punishment' means a great feast of crows, and they will remember that and return to your fields. And when there's no meat to feast on, they'll keep up the habit because there might be more soon ... but so long as there isn't they'll still gladly eat your crops too... and you will only have managed to establish your fields as the place for crows to go for good eating. So whatever else you do, don't feed failed slave-scarecrows to the birds you want to deter ...