Many investigators have illustrated the inadequacy of banding data for production of accurate survivorship data for herring gulls. Analysis of raw banding data for the Great Lakes ring-billed gull [Larus delawarensis] population similarly produced unacceptable results. A sample of 362 long aluminum bands recovered from ring-billed gulls was examined for wear. Analysis of the data computed from these bands indicated that: Wear rates were normally distributed about a mean value of 9.55% per year weight loss as per cent of the original weight. The rate of metal loss from bands was constant. The average band declined to an expected end-point weight of 252 mg of metal remaining (65% worn) 6.81 years after banding. One band per 1000 is predicted to withstand 19.6 years of wear by ring-billed gulls. Survivorship of bands is predictable, given a large enough sample of bands worn by a particular sp. In this ring-billed gull population band loss begins to depress recovery rates between the 4th and 5th year, and after the 6th year assumes a constant rate of 38% per year of the surviving bands. Correction factors computed from the study of band loss were applied to raw banding data. This produced a corrected estimate of survivorship in this ring-billed gull population, where 49.7% of the fledglings survive to age of 1st breeding, 13% of the adults die annually, and a fledgling rate of 0.523 chicks per pair of adults maintains a stable population size. Uncorrected banding data required 1.78 fledglings per pair per year to maintain stable population size. With the corrected data, even if no gulls breed until their 3rd year, and none contribute young after their 25th year, only 0.63 fledglings per pair per year will keep this population stable. Monel bands offer a reasonable alternative to provide accurate raw banding data for gulls, but not for spp. which defecate on their legs. Monel bands recovered from Caspian terns were corroded. Accurate survivorship curves for the Caspian tern population of the Great Lakes based on banding data were obtained because aluminum bands wear very slowly on this sp. The theory that salt water corrodes aluminum bands rapidly is not supported.