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Age-Class Determination of Canvasbacks

1982; Wiley; Volume: 46; Issue: 4 Linguagem: Inglês

10.2307/3808222

1937-2817

Jerome R. Serie, David L. Trauger, Harold A. Doty, David E. Sharp,

Animal Behavior and Reproduction

A technique was developed to distinguish yearling from adult canvasbacks (Aythya valisineria) in the field during spring on the basis of white flecking on the distal ends of selected wing feathers. Covert feathers from adults had well-defined vermiculation patterns whereas feathers from yearlings lacked such markings. These age-related characters were confirmed by paired comparisons of feathers from the same captive birds in consecutive years and by discriminant analysis of feathers using densitometric measurements from known-age wild birds. Reflective densitometric measurements of greater secondary coverts for females and males were significantly different between 1and 2-year-old and between 2and 3-yearold canvasbacks. Greater secondary coverts were the best feathers for recognizing age-classes of males and females. Densitometric values indicate low variability among different observers and within samples. J. WILDL. MANAGE. 46(4):894-904 The ability to recognize age-classes within a population is important in understanding aspects of reproductive biology and population dynamics (Trauger 1971, Johnson 1978, Krapu and Doty 1979, Raveling 1981). Due to the low population status of the canvasback in recent years, the influence of breeding age on individual productivity has been of concern (Olson 1964, Trauger 1974b, Bellrose 1976). A reliable technique for distinguishing between age-classes of canvasbacks in spring was needed to identify the influence of age on reproductive success of yearlings and older, experienced birds. Techniques for separating age-classes, recently developed for other species of waterfowl, use several variables which complicate their application and reliability (Dane 1968, Dane and Johnson 1975, Blohm 1977, Krapu et al. 1979, Wishart 1981). Based on feather dimensions or distinctive markings, these techniques use key wing feathers or a combination of feathers to establish criteria for separating age-classes. White flecking or vermiculation patterns on the wing coverts of canvasbacks were recognized by Carney (1964) as a valuable criterion for separation of ageclasses. He developed a technique, primarily for use during the fall, which depended largely upon shape, wear, and degree of white flecking on the tertial feathers. This technique is less effective during the breeding season because of feather wear and replacement. The objectives of our study were to (1) identify wing feathers which reliably distinguish yearlings from older canvasbacks in the field at any time of year, and (2) develop a technique for quantitatively measuring these age-related characters. We acknowledge the Data Production Division of the EROS Data Center, U.S. Geological Survey, Sioux Falls, S.D., and in particular J. McCord and C. Lawson for assistance in development of densitometry for feather age classification techniques; E. L. Ferguson for encouragement; M. I. Meyer for preparing drawings of feathers; F. B. Lee for supervising the rearing of known-age canvasbacks; D. H. Johnson for assistance 1 Present address: Division of Wildlife Ecology Research, U.S. Fish and Wildlife Service, Washington, DC 20240. 2 Present address: U.S. Fish and Wildlife Service, Box 26A, Route 1, Fergus Falls, MN 56537. 894 J. Wildl. Manage. 46(4):1982 This content downloaded from 157.55.39.27 on Wed, 07 Sep 2016 06:34:55 UTC All use subject to http://about.jstor.org/terms AGE-CLASSES OF CANVASBACKS * Serie et al. 895 with statistical analysis of data; and H. F. Duebbert and D. H. Johnson for editorial review of the manuscript.