chest i would say was a no go all together 9 times out of 10 the bird will fly away and become fox food whitch isnt good thing if you are hungry or the ferrets are hungry.
neak,head or if the shot is taken from behind right at the top of the back/lower neak. that always works for me.
pigeons seem to be like asama binlarden no one can get near them and it takes perserverience (sorry for the spelling lol)
happy hunting
all the best liam