Senescence is a decline in body function with advanced age that manifests itself in birds as a decrease in survival rates or reproduction. Senescence is difficult to study in free-ranging birds because few birds reach old age and few studies last long enough to identify those birds that do. For 21 years, I studied lifelong reproduction among Canada Geese (Branta canadensis) nesting in New Haven County, Connecticut. These data were used to determine the impact of old age on female and male fecundity during the current year and during the remainder of the birds' lives. Old-aged geese were relatively common in this population; 15% of recruited geese lived 10 years, 3% lived 15 years, and one female lived 20 years. Females that nested when they were between 5 and 9 years old had a mean clutch size of 4.5, brood size at hatching of 3.4, and brood size at fledging of 2.9. Females that nested when they were at least 10 years old had a mean clutch size of 4.7, brood size at hatching of 3.4, and brood size at fledging of 3.3. These variables were independent of age for both sexes. Future reproduction (number of future nesting years and future production of eggs, hatchlings, and fledglings) declined with parental age for males but not females. Body mass of nesting birds did not change with age for either males or females. These results provided evidence of an effect of senescence in male Canada Geese but not females. The terminal investment hypothesis (i.e., that parental investment should increase as birds become older) was not supported for either sex.
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Vol. 36 • No. 3