Answer: Bluebirds need a gourd that is at least 5 inches in diameter (so they can turn around) and the hole size should be 1.5 inches. Purple martins need a gourd minimum size of 8-13 inches and the hole size should be 2.5 inches. The holes should be at least 4 inches from the base of the gourd, so that birds can build up the nest from the base and still hop down into the nest. This also protects fledglings from falling out. As for keeping out sparrows, that seems to be an age-old problem! I suggest you contact the Purple Mountain Conservation Association, Edinboro University of Penn., Edinboro, PA, 16444, 814-734-4420. They might have some ideas. Other bird groups, such as the North American Bluebird Society (sorry, I don't have their address) or the Audubon Society might have strategies. Good luck!
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