Birds do not feel chilli heat. Their heat receptor, TRPV1, does not react to capsaicin, so they eat ripe pods and spread the seeds whole.
Birds do not experience the sensation of heat when consuming spicy foods due to the fact that they are generally not sensitive to capsaicin, the compound responsible for the spiciness in chili peppers. While capsaicin acts as a deterrent to mammals due to its heat-inducing properties, birds are largely unaffected by it. Mammals chew and destroy seeds, but birds swallow them whole and spread them far and wide!
Birds do have a TRPV1 heat receptor, but unlike ours it does not respond to capsaicin, so they do not experience the sensation of heat or pain when consuming spicy foods.
One theory for why birds are not deterred by capsaicin is related to the dispersal of chili pepper seeds. Birds play a significant role in spreading the seeds of chili peppers, as they consume the fruits and then excrete the seeds intact, helping the plant to propagate. Since birds are not affected by capsaicin, they can freely consume chili peppers without being deterred.
Scientists call this directed deterrence: capsaicin keeps seed-crushing mammals away, while birds, which pass the seeds intact, keep eating the fruits and spread the plant.
Read the full season in my Garden Diary 2024.
Why it matters for growers: Birds will happily strip ripe pods from plants outdoors, so we net our chillies once the fruit starts to colour.
Source: Jordt and Julius, Cell (2002)