Estimating Ages of Gray Squirrels by Lens-Weights

Abstract

The lens-weight technique was used to estimate the ages of 885 gray squirrels (Sciurus carolinensis) during 1965 and 1966. This method was compared with the X-ray method of aging. Agreement between the two methods indicated ffiat the lens-weight method, when used alone, is sufficient aging criterion for separation of juveniles and adults and for estimating year classes of adult gray squirrels. Statistical analysis revealed no significant difference between lenses of individual squirrels or between lenses of male and female squirrels of approximately the same estimated age. ESTIMATING AGE OF GRAY SQUIRRELS BY LLNS-WEIGHTS * Fishver and Perry 825 rather than visual cues. Animal Behavior 16(1):13-17. , S. D. PALMATEER, AND R. E. MARSH. 1969. A body capacitor-olfactometer for squirrels and rats. J. Mammal. 50(4) :771776. SIEGMUND, O. H. ( Editor ) . 1967. The Merck veterinary manual. 3rd ed. Merok & Co., Inc., Rahway, New Jersey. 1674pp. STECHER, P. G. ( Editor ). 1960. The Merok index of chemicals and drugs. 7th ed. Merok & Co., Inc., Rahway, New Jersey. 1641pp. U. S. DEPARTMENT INTERIOR. 1947. Facts about 1080. U. S. Dept. Interior Fish and Wildl. Serv., Wildl. Leaflet No. 287. 2pp. . 1959. Characteristics of common rodenticides. U. S. Dept. Interior, Fish, and Wildl. Serv., Wildl. Leaflet No. 337. 4pp. ZUCKER, M., AND W. E. EIOWARD. 1968. A transistorized body capacitance relay for ecobehavioral studies. Animal Behavior 16 ( 1 ): 6546. Received for publication August 2S, 1969. Body weight, tail pelage, degree of sexual development, and other morphologieal eriteria have been used in aging tree squirrels. None of these methods have proved completely reliable. Petrides (1951) suggested that epiphyseal elosure of the radius and ulna bones could be used to determine age differenees in gray squirrels and Carson ( 1961 ) validated its use in aging both fox (S. niger) and gray squirrels. This technique involves the analysis of the degree of epiphyseal closure and ossification and is probably the most accurate method presently used. Lord ( 1959, 1961), Sanderson ( 1961 ), Martinson et al. ( 1961) and others demonstrated the reliability of using the dryweight of the crystalline lens as an age 1 Present address: Department of Biology, Averett College, Danville, Virginia. 2 Present address: Department of Biology, \;Valla Walla College, College Place, Washington. indicator in various mammalian species. Beale (1962) found this method valid fot separating fox squirrels into summer-born, spring-born, and adult age categories by correlating lens-weights with X-ray analysis. The present study indicates that the ages of gray squirrels can be estimated by use of the lens-weight method. The population age structure analysis is comparable using both methods. The writers are grateful to W. Wheeler, Shelby Wildlife Area Supervisor, for the use of facilities at the area checking station and A. Olexik for aid in the X-ray analysis. This study was supported in part by a Memphis State University Faculty Research Grant made to A. Perry.