Lens Weights of Ring-Necked Pheasants

Abstract

Differences between lens weights of 275 adult male and 338 juvenile male ring-necked pheasants (Phasianus colchicus) collected in October, and between the adult males and 70 adult females, collected in August and midwinter, were highly significant. Correlations of lens weight and body weight with spur length among adult males and tarsal depth among adult females were also highly significant. Lenses were found to be about 95 percent developed by 7-8 months of age, and there was no evidence of continuation of lens growth after the first year. Eyeballs were collected from ring-necked pheasants in South Dakota primarily to determine if the lens-weight technique showed promise for separating year classes among adults, and if the expense of a further study using birds of known age might be justified. Secondarily, data were collected on the value of lens weights in separating adults and juveniles and the relationship of other body measurements to lens weights. Lens weights have been found useful as indicators of age in several species of mammals (Lord 1959, 1961; Sanderson 1961; Kolenosky and Miller 1962; Beale 1962). The lens-weight technique has been less successfully applied, however, in several species of birds (Payne 1961, Campbell and Tomlinson 1962, Dahlgren et al. 1964). MATERIALS AND METHODS Eyeballs were taken from shot or roadkilled adult females in eastern South Dakota during August, 1963, and in January and early February of 1964. Adult and juvenile cocks shot by hunters during the period October 19-26, 1963, were sampled at a locker plant in Huron. Left eyeballs were removed only from birds which appeared to have been shot the same day. The eyeballs were stored in 10 percent formalin solution for periods ranging from 3 weeks to 3 months before lenses were extracted. Each lens was rolled gently in the fingertips to ' This study was done under Federal Aid in Wildlife Restoration Project W-75-R in South Dakota. This content downloaded from 207.46.13.111 on Tue, 09 Aug 2016 04:21:28 UTC All use subject to http://about.jstor.org/terms LENS WEIGHTS OF PHEASANTS ? Dahlgren et al. 213 Table 1. Lens weights of pheasants. ADULT JUVENILE CATEGORY MALE Female (OCTOBER) Male Female (Mid(October) (August) winter) Number 338 275 32 123 Range (mg) 18.523.020.620.029.5 34.4 29.2 28.1 Average 23.7 30.0 24.9 24.3 Standard deviation 2.17 1.84 1.76 1.58 remove traces of the ciliary attachment. Lenses were then oven-dried at 80 C for at least 72 hours and weighed on an electrical balance to 0.0001 gram. Age was determined by use of spur characteristics, gross appearance, or bursal examination. Sex was determined by appearance or by gonadal examination. Each adult male sampled was weighed to the nearest ounce, and its spur length measured to the nearest 0.1 mm. Adult females collected in midwinter of 1964 were weighed, and a tarsal-depth measurement taken at the midpoint of the tarsus. RESULTS AND DISCUSSION The mean difference between the greater lens weights of 275 adult males collected in October and 70 females collected in August and midwinter (Tables 1 and 2) was highly significant (t = 28.12). The mean difference between the lenses from 275 adult males and 338 juvenile males was also highly significant (t = 12.06). Weights of adult lenses did not show groupings or gaps indicative of yearly ageclasses. Apparently lens weight does not increase appreciably after the first year. If there is an increase after the first year, this growth is masked by the normal variations among individual birds. This conclusion is supported by studies of other species of Table 2. Summary of lens data from 123 female pheasants collected in midwinter, 1964. CATEGORY IMMATURE QUESTIONABLE ADULT AGE