Cinnamon is considered a beneficial addition to bird diets, though only Ceylon cinnamon will do, as cassia, or Chinese cinnamon, contains higher levels of toxic coumarin.
Meanwhile, squirrels don't like the taste of cinnamon. Its strong smell irritates nasal passages and masks the smell of bird feed, making it harder to find.
Ants are also purportedly repelled by cinnamon. It stops "ants from approaching the feeding zones for hummingbirds," says ornithologist Zach Hutchinson.
However, NestWatch, a Cornell Lab of Ornithology blog, mentions a nest box caretaker who tested the ant-cinnamon theory and claimed that it failed to keep ants out of bird nests.
Given the conflicting information on this trick, it's worth conducting your own experiments. If you decide to apply cinnamon, dust it onto the pole or hook of the feeder.