Ive noticed a large number of the corvids visiting my garden are all loosing significant feathers on their heads. A few of the jackdaws are almost completely bald, magpies mainly round their eyes and this morning I've noticed one of the pair of big crows os begining to lose them now too? None of the other birds that visit show the same problem and ive never noticed this before? Is there somthing they are lacking I cab add to their feed?