from wiki
The seeds of Capsicum plants are dispersed predominantly by birds: in birds, the TRPV1 channel does not respond to capsaicin or related chemicals (avian vs. mammalian TRPV1 show functional diversity and selective sensitivity). This is advantageous to the plant, as chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, whereas mammals have molar teeth which destroy such seeds and prevent them from germinating. Thus, natural selection may have led to increasing capsaicin production because it makes the plant less likely to be eaten by animals that do not help it disperse.
And that's why TX has wild chiltepin or pequin peppers growing everywhere. Of which the plant I am overwintering in the house, which grew from seeds our Texian friend kaywoodie sent me, which didn't produce last summer, I'm hoping will give me some of them dang bird peppers so I can put them in my posole!
Geno
PS, funny thing, my chickens apparently don't like the little red, yellow, orange mini-peppers as I tossed some parts out the other day and they are still in the litter in their pen.