A review of mammalian age determination methods

Teeth: List of tables

Summary

A growing requirement exists to determine the ages of the larger African mammals, concomitant with increasing management. Teeth offer the most practicable means of age determination, but no wholly reliable method, based on teeth, has been demonstrated. Tooth structure, growth and function, are considered, and related to methods of age determination. Methods are divided into those separating groups, and those for determining the chronological ages of groups. The various methods used in these two procedures are evaluated. It is pointed out that studies on the most promising method, cementum line counts, have been neglected in Africa, while methods of determining the ages of large carnivores are virtually uninvestigated, and there is a lack of basic studies describing tooth growth and changes for most large African mammals.

A review of the age determination of mammals by means of teeth, with especial reference to Africa

Population dynamics of common and rare helminths in cyclic vole populations

During 1954–56 we made a study of the numerical relationships between a population of Tawny owls (Strix aluco) and populations of their main prey species, the Bank vole (Clethrionomys glareolus) and the Wood mouse (Apodemus sylvaticus), in a 48.6-ha area of mainly deciduous woodland near Oxford. The owls were censused by plotting their territorial challenges (hooting), the rodents by the capture-mark-recapture technique. Since the rodents were marked with numbered monel metal leg rings, we were able to recover a proportion of these in the pellets of undigested material cast by the owls.



The results for Bank voles, which were the more numerous of the two prey species, indicated that 20–30% of the standing crop was removed by owls in any two-month period. We also made an independent estimate of predation rate from the number of rings recovered from owl pellets in relation to the number of ringed rodents released into the population each two months. This coincided with the limits indicated by the first method for voles (20-30% removed of the standing crop each 2 months).



Wood mice were scarcer than Bank voles and were not amenable to satisfactory capturemark-recapture analysis but, when treated on the system of recovery of rings in owl pellets, we found that they were preyed upon relatively more heavily than were the voles. Of the latter 18–46% of the marked animals were recovered in the owl pellets compared with 28–70% of the marked mice. Either the mice were preferred prey or they were more vulnerable to owl predation by reason of their preference for more open habitats.

Predation by Tawny owls (Strix aluco) on Bank voles (Clethrionomys glareolus) and Wood mice (Apodemus sylvaticus)

In the bank vole (Clethrionomys glareolus (Schr.)) the relatively large first molar in the mandible has been a natural choice as an indicator of age (Zimmermann 1937; Wasilewski 1952; Koshkina 1955; Zejda 1961; Mazaik 1963), chiefly because, although rootless when it first erupts, an oral and aboral root are developed subsequently, and these then continue to grow throughout life until, in old age, only the roots remain, the entire crown having been worn away. Various estimates of the time taken for roots to develop and of their subsequent growth rate have been made by different authors, some using large samples of animals from the field, collected after different intervals of time, while others have used laboratory animals of known age, or a combination of both sources of material. Partly because of the different methods used, and partly for other reasons, discussed later, estimates of the age at which the molars first begin to develop roots have varied widely, ranging from 2 months (Wasilewski 1952) to 6 months (Zimmermann 1937), and the rate of growth of the roots has been estimated to vary between 0-12 and 0-161 mm/month, averaging 0d15-016 mm/month (Zejda 1961), but only teeth from individuals 11-16 months of age were measured. To obtain if possible a more general correlation between age and root development, an attempt was made to stain the calcium being laid down in the roots at standard intervals of time, by injecting the voles with sodium alizarine sulphonate, a water-soluble and acid dye, used for gross skeletal staining. Both laboratory and field populations were used in these experiments, which were carried out under licence from the Home Office at the Bureau of Animal Population in Oxford, and in some nearby woodlands on the Wytham estate between 1954 and 1957.

V. P. W. Lowe

Papers

Root Development of Molar Teeth in the Bank Vole (Clethrionomys glareolus)