Weights and Growth Characteristics of Pheasant Lenses

Abstract

Variations in the dry weights of eye lenses of 130 known-age pheasants (Phasianus colchicus) indicated that weights could not be used to satisfactorily separate (1) juvenile cocks and juvenile hens into monthly age-classes; (2) juvenile cocks, older than 5 months, from adult cocks, and juvenile hens, older than 3 months, from adult hens; and (3) adults of either sex into yearly age-classes. Lens weights of adult cocks were, without exception, greater than those of adult hens. A multiple regression analysis revealed that both body weight and age exhibited a significant linear dependence with lens weight when the two variables were considered separately; when the two variables were considered together, lens weight was significantly dependent on age but not on body weight. The regression model for the lens weight versus age curve was logio (y) = a + b ( +5) where y denotes lens weight and x denotes age. The dry weight of the lens was first described as an indicator of age by Lord (1959) for the cottontail (Sylvilagus floridanus), and has been subsequently found useful as an aging criterion for many species of wild mammals. Among birds the use of lens weights for determining age has been much less successful. Payne (1961) reported that lens weights were unsatisfactory for ascertaining the ages of house sparrows (Passer domesticus) older than 2 1 A contribution from Illinois Federal Aid Project Nos. W-30-R and W-42-R, the Illinois Department of Conservation, the U. S. Bureau of Sport Fisheries and Wildlife, and the Illinois Natural History Survey, cooperating. 2 Present address: Arbovirus Unit, Communicable Disease Center, U. S. Public Health Service, Atlanta, Georgia 30333. he dry weight of the lens was first demonths. Campbell and Tomlinson (1962) found that although the mean lens weights of juvenile and adult Turkish chukars (Alectoris graeca) differed significantly, there was a frequent overlapping of individual lens weights between these two age groups. Roseberry and Verts (1963) found that the overlap in lens weights of juvenile and adult bobwhites (Colinus virginianus) was too great to permit reliable separation of these two age groups in autumn. Similarly, Dahlgren et al. (1964) reported considerable overlap between lens weights of juvenile and adult sharp-tailed grouse (Pedioecetes phasianellus) collected in au-