Once you get your bird feeding station up and running, you may run into problems with two kinds of uninvited guests - those interested in the seeds (squirrels and chipmunks, rats and mice, and starlings and house sparrows), and those interested in eating a bird for dinner (cats and hawks).
When a squirrel is at the feeder, you're not likely to see birds. Squirrels will scare off the birds while they eat the seed and sometimes they will eat the feeder too. The simplest solution is a squirrel-proof feeder or pole.
Starlings and house sparrows are not native to North America and are aggressive towards other species. Choose your feeder and seed to exclude these species if possible.
Chipmunks, rats and mice can also become a problem where there is seed spillage under the feeder. Don't use mixed bird seed, and if you don't have a squirrel problem, add a feeder tray.
Feral cats and your neighbor's tabby are a serious threat to many birds. Keep feeders away from brushpiles and shrubbery, as this offers cats the necessary cover to surprise birds.
If there are no cats in your neighborhood and you find a pile of feathers near your feeder, look for a full-bellied hawk perching on a tree nearby. Don't put out poisons or try to trap hawks though, as this is against state and federal law.