Squirrel-Proof Birdseed Doesn't Exist

For anyone with bird feeders in their yard, it is important to know that there really isn't a birdseed that squirrels won't eat. Emma Greig, a scientist and project leader researching this topic, "We don't recommend cayenne because, though it's probably harmless for birds, there haven't been any really careful studies about it. We tend to err towards recommending that people not add stuff to bird seed.