Are birds repelled by capsaicin?

Q: To deal with an extreme squirrel problem I added some chili powder and cooking oil to sunflower seed. Now only cardinals visit my feeder. Could it be too hot? 

A: I think the change in bird feeder visitors is likely to be more from seasonal variation than from your pepper being too hot. Research from Cornell University showed that birds simply don’t have a receptor for capsaicin, the hot stuff in hot peppers. Mammals, on the other hand, do have pain receptors that are stimulated by capsaicin. I found one paper that noted that squirrels were deterred from three feeding stations treated with various levels of capsaicin but chipmunks were not. I have no idea why that happened. More research is needed!