Yellow-bellied Sapsucker (Sphyrapicus varius) Science Article 6
Power (1975, Science 189: 142) presented the theory of altruism in describing experiments designed to test it on wild Mountain Bluebirds (Sialia currucoides). He considered his results negative, but they are pertinent to observations I presented briefly (Kilham 1971, Wilson Bull. 83: 159) but not in detail, on a natural experiment that involved anotherhole-nesting bird, the Yellow-bellied Sapsucker (Sphyrapicus varius).
LAWRENCE KILHAM, The AUK (94)