As far as I'm concerned,I just increased the remaining animals food supply.This way they shouldn't have to be bothering my chickens.They shouldn't have to compete as much for the food sources.
Animals migrate anyway,while still sticking to a home range.The more there are,the faster the diseases spread.
If you leave the animals alone,it just makes it spread faster.
Plus if I let it live,there's no tellin how many litters it could have continued to breed.
Don't get me wrong,it's not something I enjoy doing,but definitely necessary.
I'd think that animals tend to migrate when they're hungry,meaning that too many animals,with limited amounts of food tend to compete more for that food.Hence they migrate.While spreading whatever they may have.