A bird feeder is provided with a containing structure including an internal space and at least one feeding opening on an outer surface of the containing structure and communicating with the internal space； a perch including a central bossed hole with the containing structure disposed through, and a channel disposed through a surface of the bossed hole wherein the perch is disposed under the feeding opening and configured to slidably, longitudinally move on the containing structure； at least one positioning device disposed through the channel to urge against the containing structure for fastening the perch and the containing structure together； and a blocking roof releasably disposed on the containing structure and above the feeding opening. A height difference between the blocking roof and the perch is adjustable.
