| Summary: | Abstract Background Oxidative stress, caused by an imbalance between reactive oxygen species and antioxidants, is thought to be an important intrinsic mechanism for aging. Ecologists have tested this hypothesis in birds, although the evidence supporting the link between oxidative stress and lifespan has so far been ambiguous. Two previous studies based on a wide range of different free-living bird species provided contradictory findings: antioxidants were negatively associated with survival rate in one study, but positively associated with longevity in another. Methods In this study, we identified possible shortcomings in previous research, and then used the comparative methods to test whether long-lived birds experience less oxidative stress reflected by four blood redox state markers (total antioxidant status, uric acid, total glutathione, malondialdehyde) based on data for 78 free-living species. Results Relatively long-lived bird species had high levels of antioxidants (total antioxidant status, total glutathione) and low levels of reactive oxygen species (malondialdehyde). These associations were independent of statistical control for any effects of body mass, sampling effort and similarity among taxa due to common phylogenetic descent. Conclusions The direction of these associations is consistent with the oxidative stress theory of aging.
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