When a photo of a chupacabra appears in the news, it tends to be a shriveled, hairless, canine-looking corpse. According to University of Michigan biologist Barry OConnor, these chupacabra corpses are simply coyotes with sarcoptic mange (a.k.a. scabies).
The scabies mite is an annoyance for humans and domesticated dogs but can be devastating for wild dogs — the mites cause skin inflammation, hairlessness, and skin infections, which explains the chupacabras mottled appearance and horrific body odor. Furthermore, livestock becomes a more attractive food source for the infected coyotes, as they don't have to expend as much energy chasing them down. Says OConnor:
Whenever you have a new host-parasite association, it's pretty nasty [...] It does a lot of damage, and mortality can be relatively high because that host species has not had any evolutionary history with the parasite, so it has not been able to evolve any defenses like we have [...] So they may be forced into attacking livestock because it's easier than running down a rabbit or a deer.
While this isn't exactly surprising news, it's always welcome to hear the science of the legendary goat-sucker. Now all we need is a rational explanation for the Mothman.