An Attempt to Age Mallards Using Eye Lens Proteins

Abstract

An analysis of insoluble protein content of eye lenses from 59 known-age mallards (Anas platyrhynchos) indicated a slight increase between 8-9 months and 7 years of age. Nearly a complete overlapping of the insoluble protein content of individuals of different ages was apparent showing that the technique cannot be used to separate adult year classes of mallards. These results are contrary to findings reported for selected mammalian species; a possible explanation for the dissimilarity is discussed. J. WILDL. MANAGE. 38(1):138-141 An understanding of the age structure of a population is one of the most powerful tools of the wildlife investigator; however, there is no reliable procedure for determining the age of birds after attainment of sexual maturity or adult plumage. At present, the only data available for determination of life span or survival comes from marked or banded birds. Lord (1959) showed that the dry weight of the eye lens can be used to determine the age composition of cottontail rabbit (Sylvilagus floridanus) populations, and numerous other investigators have studied the relationship between lens weight and age in a variety of wildlife species (review by Friend 1967). This aging technique also was attempted in the early 1960's with several species of birds (Payne 1961, Campbell and Tomlinson 1962, Roseberry and Verts 1963, Dahlgren et al. 1964, Dahlgren et al. 1965); none of these attempts successfully separated adult year classes. Otero and Dapson (1972) discussed a biochemical technique employing insoluble eye lens protein concentrations for estimating the age of vertebrates. According to Krause (1934) and Davson (1962), proteins make up about 35 percent of fresh lens weight. Insoluble protein in the lens of the eye increases with age in selected vertebrate species, including old-field mice (Peromyscus polionotus) (Dapson and Irland 1972). Dische et al. (1956) showed that water soluble protein is first added to the growing lenses but that this protein becomes insoluble with age. The present study was designed to test the feasibility of measuring the insoluble protein in order to age mallards to year class. Hand-reared mallards of known-age (89 months to 7 years) from the Northern Prairie Wildlife Research Center, Jamestown, North Dakota, were used in the study. We acknowledge the cooperation of H. K. Nelson and F. B. Lee in providing the known-age stock. F. B. McGilvrey made facilities available at the Patuxent Wildlife R search Center for the mallards, and his assistance is appreciated. MATERIALS AND METHODS The methods employed for the isolation and determination of insoluble protein in mallard eye lenses were those of Otero and Dapson (1972). Birds were sacrificed by cervical dislocation. The eyes of known-age mallards were carefully removed within 12 hours after death. The eyes were placed in aluminum foil boats and kept on ice until the lenses were removed. Lenses were removed as described by Otero and Dapson (1972). Considerable care was taken to avoid rupturing the lenses and to remove 138 J. Wildl. Manage. 38 (1):1974 This content downloaded from 40.77.167.74 on Tue, 20 Sep 2016 05:51:41 UTC All use subject to http://about.jstor.org/terms ATTEMPT TO AGE MALLARDS * Henny and Ludke 139