Growth of the Eye Lens in Relation to Age in Fox Squirrels

Effects of Nest Boxes on Fox Squirrel Demography, Condition and Shelter Use

“…After the removal of both eyes and a forepaw for aging, carcasses were frozen until they were autopsied. Squirrels were aged using lens weight (Beale, 1962) and epiphyseal closure (Carson, 1961). After thawing, wet weight was determined for the carcass (minus the stomach) and selected organs.…”

A review of mammalian age determination methods

“…An example of a size frequency histogram. Lens weights in an autumn sample of fox squirrels (redrawn from Beale, 1962). The relative incidence of various weight categories is shown, together with Beale's interpretation of the results in terms of age classes.…”

“…Connolly, Dudzinski & Longhurst (1969a) suggest that there are statistical advantages to be gained, especially with respect to very old animals, if the log of the lens weight is used (as described by Dudziriski & Mykytowycz, 1961). Beale (1962) was able to separate juveniles and adults in the Fox squirrel (Sciurus niger) and first and second litter young as well. For many mammals, if a growth curve based upon known age animals is available for reference, animals less than 1 year old can be aged to the nearest month, and those more than 1 year old can be assigned to a definite year class.…”

“…Perry & Herreid (1969), using the minute lenses of the Free-tailed bat Tadarida brasiliensis achieved a fair correlation with age (already known from bat banding studies) that was anyway as good as results based upon tooth wear. However, in contrast to this, it would appear that in laboratory mice (Mus musculus) the mean lens weight at any particular age has such a large variance as to be valueless for comparison with mice trapped in the wild (Berry & Truslove, 1968). Genetical differences between inbred strains were also observed.…”

Evidence for a Relationship between Longevity of Mammalian Species and a Lens Growth Parameter

“…1986;Hockwin et al, 1986], rat (Rallus norvegicus) [Hockwin, 1978;Tréton and Courtois, 1981;Hockwin et al, 1986], cotton-tail rabbit (Sylvilagus JJoridanus) [Lord, 1959;Edwards, 1962;Rongstad, 1966], Australian rabbit (Oryctolagus cuniculus) [Dudzinski and Mykytowycz, 1961;Edwards, 1962], swamp rabbits (Sylvilagus aquaticus) [Martinson, 1961], guinea pig (Cavia porcellus) [Hockwin et al, 1971;Hockwin, 1971;, raccoon (Procyon lotor) [Sanderson, 1961;Montgomery, 1963], gray fox (Urocyon cinereoargenleus) [Lord, 1961], dog (Canis familiaris) [Hockwin et al, 1986], fox squirrel (Sciurus niger) [Beale, 1962], pronhorn antelope (Antilocapra americana) [Kolenosky et al, 1962], white-tailed deer (Odoceilous virginatus) [Lord, 1962], Columbian black-tailed deer (Odocoileus hemionus colombianus) [Longhurst, 1964], mule deer (Odocoileus hemionus hemionus) [Longhurst, 1964], fur seal (Callorhinus ursinus) [Bauer, 1963], cow (Bos laurus) [Hockwin et al, 1963], elephant (Loxodonta africana) [Laws, 1967], and man (Homo sapiens) [Johansen, 1947;Graeber, 1966;Larsen, 1971;Nordman et al, 1974], Fig. 1.…”