A) I am sure that the dead and sick woodpigeon are not suffering from acorn poisoning, for while overeating acorns can kill some livestock, it will not, as far as I know, affect pigeon. The most likely explanation is a protozoan parasite called trichomoniasis, also known as frounce. If you open the beak of a bird you will probably see a cheesy matter in the gape, a sure sign that the bird has this disease. Pheasants can get frounce, but they should be safe from it by now and I have never seen it manifest itself in the way it is affecting your pigeon. It may be that this is a different strain of the disease and that, rather like coccidiosis, it is species-specific: partridge coccidiosis, for example, does not affect pheasants.