AGE CRITERIA FOR THE AFRICAN ELEPHANT

LOXODONTA A. AFRICANA

Authors


Nuffield Unit of Tropical Animal Ecology, P.O. Queen Elizabeth Park, Uganda2

Summary

1. The paper is based on a collection of 385 lower jaws of the African elephant (Loxodonta a. africana Blumenbach) from western Uganda.

2. Thirty age groups are described and illustrated, which are related to the progress of eruption and wear of the six teeth in each side of the lower jaw.

3. Correct identification of individual teeth in the series is essential and several checks are described. Thus, when length is plotted against width for the six teeth the points fall into six well - defined groups. Frequency distributions of laminary indices and lamella numbers support the belief that teeth have been correctly identified, but overlapping, distributions preclude identification on these characters alone.

4. The presence of abnormal seventh molars in four jaws is described.

5. Chronological ages have been assigned to the relative age groups. Information on age and growth of captive animals has been considered and the general form of the growth curve established. Arbitrary estimates of the intervals between successive age groups were made and subsequently checked against growth and seasonal ridges on the roots. These indicate an upper age limit of about 60 years, which is compatible with fuller information on Indian elephants.

6. Growth curves support the validity of the ages assigned. Asymptotic heights at shoulder (∞) are respectively 317 cm and 298 cm for males from Murchison Falls and Queen Elizabeth National Parks. For females no distinction is made (because the sample from the latter area is small) and ∞ is 272 cm.

7. Growth in weight has also been established but shows no significant differences between the two populations. The mean maximum weight of females is 2766 kg (6100 lb), and of males 5450 kg (12000 lb). Growth apparently continues throughout life.

8. Tusk growth is analysed. There is a linear increase in weight of female tusks from eruption at 1–3 years up to the oldest group, with an indicated mean combined weight of 17.7 kg (39 lb) at 60 years. Male tusks show an increasing rate of growth throughout life to a mean combined weight of about 109 kg (240 lb) at 60 years.

Big tusks are generally the result of prolonged growth; extremely big tusks probably result from prolonged and above average rate of growth.

9. Seasonal and annual incremental layers on the root 3 of the teeth are briefly described; these give an objective estimate of the chronological intervals between the relative age groups.

10. Field age criteria are presented which are derived from these growth curves.

11. The age at puberty in the female elephant is discussed and compared with earlier conclusions. There is evidence of a retardation in recent years in the Murchison Falls National Park (South bank) population and of a lengthening of the mean calving interval. This considerable depression of the reproductive rate, which is almost certainly density dependent, agrees with the observed lower recruitment in this population.

12. Survivorship curves constructed from material representing 325 natural deaths are presented for the two populations. If estimates of the age at puberty and the reproductive rate are taken into account, the expected differences in recruitment are found.

13. The calculated mean expectation of life is less than 15 years.

14. Mean individual weight is estimated at about 3800 lb.

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