Rabies

[Orleander]

...A few of them will get bitten and die, but before long he will be killed and the herd will survive.

But those bitten ones will bite others who bite others. Do they have the sense to know "Uh-Oh, he got bit. Kill him before he goes insane"

 

[Fraggle Rocker]

I don't know. The fox population back home in California waxes and wanes in a three or four year cycle. They come around every night... and then a year or two later there simply aren't any at all. Our vet says it's because they all get rabies and die off. We have to wait for a new population to migrate in from elsewhere.