The above photo shows my Lesser Sulphur-crested Cockatoo, Mitri, enjoying a habanero pepper. Most of my parrots will eat hot peppers and Mitri in particular really seems to love them.
Most mammals, however, would not enjoy eating whole habanero peppers. They are very hot – much hotter than jalapeno or tabasco peppers. The main compound in hot peppers that causes a burning sensation in mammal tissue is called capsaicin. Capsaicins have a strong irritant effect on mammal pain sensor neurons (nociceptors), and in particular, they bind to a certain receptor molecule on nociceptors that, when activated, triggers a series of chemical reactions that the brain interprets as pain caused by damaging heat. The venom from tarantula spiders activates a similar pathway. The receptor that capsaicin binds to is called the vanilloid receptor subtype 1 (VRS1) receptor, and it also reacts to heat and abrasive damage.
Birds are different and many do not appear to be bothered by foods with a concentration of capsaicins that would cause great pain to a mammal. Bird nociceptors just don’t respond to capsaicins the way mammal ones do. Birds can therefore eat hot peppers that would badly irritate a mammal.
There may be an evolutionary explanation for this discrepancy. Many plant seeds can be dispersed by birds, if birds consume the fruits the seeds are encased in and then excrete whole seeds in their droppings. Many plant seeds can actually survive going through a bird’s digestive tract. Mammals, on the other hand, are more likely to chew their food than birds are; therefore, it is in the best interest of many plants that their seeds be ingested by birds, not mammals. The presence of a compound that irritates mammals but not birds would greatly increase the chances that a fruit would be ingested by a bird.
However, parrots are not among the birds that can disperse seeds efficiently. Parrots tend to chew their food quite well, and this includes seeds. Parrots are generally considered seed predators, not seed dispersers. Birds like toucans and aracaris, who swallow whole fruits, are often quite efficient seed dispersers.
If you’re preparing food for your parrots and decide to add some bits of hot pepper, keep this in mind in case you get some in your mouth: water is not terribly effective at dissolving hot pepper, because capsaicin is a ‘hydrophobic’ molecule. That means it is repelled by water and won’t dissolve in it. Thus, drinking water is not the best way to get the taste out of your mouth. Use (non-skim) milk instead – capsaicin can dissolve in liquids that have some fat in them. Capsaicin can also be washed off of surfaces using soapy water.