Aging and environment affect female more than male color in a mutually ornamented bird

Abstract Color ornamentation is often sexually selected as a signal of condition, which may be affected by the environment and senescence, but long-term studies in mutually ornamented species are rare, limiting our understanding of sex-specific senescence. We measured color ornamentation of 60 common waxbills (Estrilda astrild) after capture from the wild and in 4 autumns in a large open-air mesocosm. We found longitudinal decreases in the size of the red mask and redness of plumage and bill color, consistent with senescence. Bill color decreased more in females. In males, there was a longitudinal increase in the size of the red breast patch. We also found increased color ornamentation, especially in females, when moving from the wild to the mesocosm, likely due to environmental effects. Monitoring waxbills in bird cages suggested that bill and plumage redness peak in the breeding season. Stronger senescence and environmental effects in females indicate cautious investment in ornamentation, while weaker senescence in males could be due to stronger sexual selection. Overall, although similarly ornamented, the sexes differ in their temporal investment in ornamentation, in line with their life histories.