Stephanie that is crazy!! I would have thought that the odds would have surely favored more hens than roosters!
I've heard that once a dog has killed something (bird, vermin, squirrel) that they will always be more aggressive towards that thing, and
be a kill risk (don't know if this is really true, but its what a dog trainer that I know says, its partly why Seattle animal shelter has a zero tolerance policy towards dogs that have killed other dogs, or cats)