Band loss - its effect on banding data and apparent survivorship in the Ring-billed Gull population of the Great Lakes

TitleBand loss - its effect on banding data and apparent survivorship in the Ring-billed Gull population of the Great Lakes
Publication TypeJournal Article
Year of Publication1967
AuthorsLudwig JPinson

1.) 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 population similarly produced unacceptable results. 2.) 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: A. Wear rates were normally distributed about a mean value of 9.55% per year weight loss as per cent of the original weight. B. The rate of metal loss from bands was constant. C. The average band declined to an expected end-point weight of 252 milligrams of metal remaining (65% worn) 6.81 years after banding. One band per thousand is predicted to withstand 19.6 years of wear by Ring-billed Gulls. D. Survivorship of bands is predictable, given a large enough sample of bands worn by a particular species. E. In this Ring-billed Gull population band loss begins to depress recovery rates between the fourth and fifth year, and after the sixth year assumes a constant rate of 38% per year of the surviving bands. 3.) 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 first 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 third year, and none contribute young after their 25th year, only 0.63 fledglings per pair per year will keep this population stable. 4.) This method of correcting survivorship curves based on banding data can probably be applied to other species, provided that these do not remove their bands before the tags wear out and fall off unaided by the birds. Herring do apparently remove some bands used on them. 5.) Monel bands offer a reasonable alternative to provide accurate raw banding data for gulls, but not for species which defecate on their legs. Monel bands recovered from Caspian Terns were corroded. 6.) Bands of the smallest size which does not injure birds should be used, rather than loose-fitting large bands in order to minimize wear on the inside of bands. 7.) 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 species. 8.) The theory that salt water corrodes aluminum bands rapidly is not supported.