SYNOPSIS. The long life spans of birds relative to those of mammals are intriguing to biogerontologists, particularly in light of birds' high body temperatures, high blood glucose levels, and high metabolic rates—all of which should theoretically increase their biochemical liability for rapid aging. The comparative longevity of birds and other flying homeotherms is consistent with evolutionary senescence theory, which posits that species with low mortality rates from predation or accident will be released from selection for rapid maturity and early reproduction, and will exhibit retarded aging. Comparative analyses of avian life history parameters to date, although not as extensive as those for mammals, broadly support an association between low mortality rates, slow reproduction, and long lifespan. The diversity of bird life histories suggests the importance of developing a diversity of avian models for studies of aging mechanisms, both proximate and ultimate, and for using wild as well as domestic representatives. Birds studied in the laboratory thus far show many of the same manifestations of aging as mammals, including humans, and many ornithologists are beginning to document actuarial evidence consistent with aging in their study populations. We encourage greater communication and collaboration among comparative gerontologists and ornithologists, in the hope that the study of aging in birds will lead to an integrated understanding of physiological aging processes well grounded in an evolutionary paradigm.