Changes in Survival Rates of Lesser Snow Geese with Age and Breeding Status
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Survival rates of Lesser Snow Geese (Chen caerulescens caerulescens) were examined based on recoveries and recaptures of about 350,000 geese banded at breeding colonies in northern Canada, at migration stopover points in the Dakotas and Missouri, and on the wintering grounds in Louisiana and Texas. First-year survival rates for goslings banded on the breeding grounds varied from 10 to 70% of adult survival rates. Much of the juvenile mortality occurred on the breeding grounds or early on the first migration. Young geese that reached migration stopovers or the wintering grounds were more vulnerable to hunters than adults, but had only slightly lower survival rates than adults. Greater vulnerability and lower survival continued through the second year of life, even though yearlings do not breed. In contrast, older birds that did not breed, or failed early in a nesting attempt, were much less vulnerable to hunters in the following hunting season than successful breeding adults, but did not appear to have higher survival as a result. Geese captured for the first time as breeding adults had slightly lower survival rates than geese that had been recaptured at the colony at least once, suggesting experienced breeders have higher survival. Although there was some evidence that older birds were slightly more vulnerable to hunters, there were no signs of any changes in survival rate with age in older geese, indicating that senescence, if it affects survival, does not do so for at least the first 10 to 15 years of age. With current hunting levels, less than 5% of Lesser Snow Geese are likely to live beyond this age. Our study demonstrates a variety of statistical methods for testing hypotheses about age-specific survival using both recovery and recapture data, even when the data do not permit estimation of the exact survival rates.