, 2007; Costantini, 2008). Our Rapamycin failure to corroborate Møller’s (2007) results may have been due to: (1) differences in sample sizes and analytical techniques [he conducted independent contrast analyses on 169 species of European birds, whereas we analyzed means of 40 avian families (470 species) world-wide];

(2) differences in the quantification of breeding latitude (he analyzed breeding latitude as a continuous variable, calculated as the mean of the northernmost and southernmost breeding season latitude for each species, whereas we analyzed breeding latitude more conservatively as a categorical variable, with three ±30° increments, due to considerable intra-specific variability in breeding locales); (3) differences in quantification of migration (Møller analyzed mean migratory distances of entire species as a continuous variable, whereas we considered migration as a categorical variable, again due to intra-specific variability in migration distances); (4) the relatively small amount of variation in longevities (<4%) that Møller explained by considering either breeding

latitudes or migration distances. The puzzle of senescence is being actively investigated at multiple levels of analysis (Sherman, 1988; Jenkins, 2004; Monaghan et al., 2008; Ricklefs, 2008), especially in birds Nutlin-3a purchase (reviewed by Holmes & Martin, 2009). Our results indicate that much of the variation in avian Etomidate longevities can be explained by differences in body mass, diet, breeding sociality and breeding insularity. The longest-lived species were large, herbivorous, social, island-dwellers, which is consistent with evolutionary theories of senescence (Medawar, 1952;

Williams, 1957; Kirkwood, 1977, 2002) because all four traits can contribute to reducing rates of extrinsic mortality. In general, birds live longer than similar-sized mammals because flight facilitates escape from predators. Among avian families, behavioral and life-history characteristics that further reduce extrinsic mortality underlie much of the variability in maximum longevities and, probably, rates of senescence. For helpful commentaries on preliminary versions of the manuscript we thank Ronald Booker, Walter D. Koenig, John W. Fitzpatrick, H. Kern Reeve, Kaitlin Stanmyer, the anonymous reviewers and, especially, Robert E. Ricklefs and Janet Shellman Sherman. Francoise Vermeylen and Sherry Weitzen provided statistical advice; Richard Wrangham suggested the aposematism hypothesis. For financial support, we thank the US Fish and Wildlife Service, and the College of Arts and Sciences, the Agricultural Experiment Station (Hatch Grant Program), and the S.H.