This is interesting, I was under the impression that chili peppers specifically evolved (spiciness) to be edible by birds but not mammals. Maybe that's an adaptation specific to tropical birds?
Adding on: Though there is no consensus, I believe that is now the less-popular theory for the origin of spiciness. It seems instead to be a form of pesticide and fungicide.
Evidence for this is that pepper varieties tend to be spicier in wetter environments, where the biological resources spent on producing capsaicin to fight fungus are more valuable than preserving them in case of drought.
