[RachelF]

>birds have no receptors for capsaicin, while mammals do.

True. I suspect it is only placental mammals. Brush-tailed possums (a marsupial mammal) do not seem repelled by it at all. I've had my birds eyes and Carolina Reaper chilly plants and fruit eaten by them.

[msrenee]

I'm seeing quite a few websites suggesting cayenne pepper to keep Virginia Opossums out of your plants. I've never tried it myself, but that's a marsupial that appears to not like spicy food. The only species coming up in these increasingly useless search engine results as liking spicy food is Chinese tree shrews.

I'm getting so frustrated anymore trying to use google, bing, brave search, startpage, etc for finding anything except reddit or quora answers and business pages. If you find any more info on marsupials and peppers, I'd love to see it. It's a super interesting question.