Birds have few reliable indicators of aging. Pentosidine is a product of nonenzymatic glycation that accumulates in tissues of an animal over its lifespan. The intent of this study was to determine if accumulation of skin pentosidine in birds of known ages changed as a function of time. Skin samples were obtained from the breast of 45 birds of various species obtained from the national aviary. In addition, foot webbing samples were obtained from 17 California Gulls (Larus callifornicus) of known ages. Collagen was measured by a hydroxypro-line spectrophotometric method and pentosidine was quantified using reverse phase high-performance liquid-chromatography. Pentosidine concentration in the skin and foot webbing increased linearly with age (P < 0.001). Hydroxyproline concentrations from the foot webbing were comparable to that measured in the skin; however, pentosidine concentrations were approximately one-fourth of that in skin. Knowledge regarding longevity of birds could provide information for species survival programs and insight into variations in longevity of an entire population.