Age Specificity in Mallards Banded Postseason in Eastern Colorado

Abstract

Recovery and survival rates and geographic distributions of recoveries were compared for and subadult mallards (Anas platyrhynchos) banded postseason in eastern Colorado during the period 1963 through 1972. Almost 4,400 recoveries from over 51,000 bandings were analyzed. Mean recovery rates were equal for and subadult males (3.7%), and for and subadult females (1.8% and 2.1%, respectively). Mean survival rates were also nearly equal between the 2 age classes of each sex, about 76 percent for males and 69 percent for females. A much higher proportion of the total first year recoveries of males (66%) and females (50%) occurred in eastern Colorado than that for subadult males (43%) and subadult females (31%). We recommend that additional comparisons of these population parameters by age class be made for population segments of mallards in other wintering areas to see if the results obtained in eastern Colorado apply over a broader area. This would require the aging of birds during postseason banding. J. WILDL. MANAGE. 42(2):263-270 The mallard has received much attention in the study of wildlife population dynamics. Mortality begins in the egg and continues throughout life. Studies of hatching success and duckling loss normally have shown high mortality during the early stages of life (Earl 1950, Keith 1961, Dzubin and Gollop 1972). However, rates of mortality are not consistent from 1 age group to the next, at least up to a certain age. Mortality studies based on preseason banding consistently have noted higher first-year recovery and mortality rates for immatures than for (Hickey 1952, Anderson 1975, Hopper et al. 1975). General patterns of recovery distributions also differ between first-year recoveries of mallards banded preseason as immatures and those banded as (Anderson and Henny 1972). The existence of age-specific differences in these population parameters within the so-called adult stage has not received much study. The determination that such a phenomenon occurs was long hampered by the absence of a field method for aging mallards during the late fall and winter. The wing-aging technique (Carney and Geis 1960, Carney 1964), and its later application to field use (Hopper and Funk 1970), now have made it possible to address this question for certain age classes of adults. The major objectives of this study were (1) to investigate differences in recovery rates and survival rates between young adults (second year) and older adults (after second year), and (2) to examine the relationship in geographic distributions of recoveries between these 2 age groups. Specifically, parameter estimates for birds banded following completion of their first hunting season were compared with those for birds banded after exposure to 2 or more hunting seasons. Earlier postseason banding programs throughout the country, and even most banding in recent years, have simply classified all ducks as adults. There has been little or no attempt on the part of most banders to apply the wing-aging technique for separating the age classes. The opportunity to collect age data valuable in the study of the population dynamics of the mallard therefore has been ignored. 1 Contribution of Colorado Federal Aid in Wildlife Restoration Project W-88-R. J. Wildl. Manage. 42(2):1978 263 This content downloaded from 157.55.39.78 on Tue, 21 Jun 2016 06:18:12 UTC All use subject to http://about.jstor.org/terms 264 AGE-SPECIFIC MORTALITY OF MALLARDS -Hopper et al. Aging mallards postseason by use of wing plumage is not as complicated a process as many apparently believe, but, like any other method, it requires individuals well trained and experienced in the method to obtain the desired degree of accuracy (Hopper and Funk 1970). Birds with wet or muddy wings are difficult to age, but we have found that by following the basic trapping and handling techniques, the former condition seldom occurs and the latter one is practically nonexistent. Birds trapped in the winter that are too wet or muddy to age correctly normally should not be banded in the first place for obvious reasons. Care in the selection of trapping sites will eliminate most of these potential problems. Regardless of the time of year and method used in aging, banders should be certain of the age of a given bird, otherwise it must be released unbanded or designated as age unknown. Many people contributed to the overall conduct of this study. We especially would like to acknowledge those individuals who made important contributions to this effort. Appreciation is extended to J. R. Grieb, Director, Colorado Division of Wildlife, for initiating and supporting the study, and to the following individuals for their assistance in banding : C. R. Hayes, D. Home, and J. E. Randall, U.S. Fish and Wildlife Service, Division of Law Enforcement; C. E. Braun, L. L. Green, R. D. Kitzmiller, W. H. Rutherford, and M. R. Szymczak, Colorado Division of Wildlife.