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Biology - Reproduction

Reproductive parameters for Savanna Elephant

Seasonal breeding Most populations have a distinct breeding peak during the rainy season although births may occur in any month of the year
Gestation 22 months
Age at first conception The median age is probably about 10 years old but in favourable conditions some females may conceive as early as 8 years of age. Laws (et al 1975) recorded conception being delayed until 19 years of age in a high density population in Uganda.
Age at first parturition In populations not suffering density-dependence effects, about 50% of the 12 year-old females will produce calves and by the age of 15 all females will have produced their first calves
Fecundity (adults) The effect of seasonal breeding results in most elephants producing a calf every four years throughout their life after their first parturition. Fecundity may decline in the last few years before death.
Longevity Elephants are generally assumed to live to about 60 years old. On the basis of age criteria deficiencies, Craig (1992) considered it more likely that the age of senescence was about 50 years old.
Mortality (juveniles) Data on calf mortality are difficult to collect. Work on elephant life tables suggests that in normal conditions juvenile mortality does not exceed 10% in the first year of life.
Mortality (adult males) Mortality is slightly higher than in females. Young males between the ages of 20- 25 years have been recorded as suffering a higher mortality than the other adults in the population.
Mortality (adult females) Other than in times of environmental stress (drought or disease), natural mortality is very low - probably less than 0.5% per annum
Table 2: Reproductive parameters for Savanna Elephant. Derived from Craig (1984, 1992), Dunham (1988), Hanks (1972), Laws (et al 1975), Lindeque (1988), Martin (2004) and Smithers (1983).

Martin (2000b) developed a detailed population model for elephants.This model permits testing of expected breeding performance and the response to various management regimes (illegal hunting, culling, capture of live animals, problem animal control and sport hunting). It includes a density dependence function and it also costs all management activities regimes and estimates the income from ivory, elephant skin and sport hunting.

Age specific fecundity

Lindeque (1988) derived average fecundities for the female elephants in Etosha National Park in 1983 and 1985 from two shot samples which included 103 and 214 females respectively. His finding was that, over their main breeding life span, the females were producing almost exactly one calf every four years (i.e. a fecundity of 0.25 including calves of both sexes). In 1983 no animals under the age of 12 years were pregnant or lactating but in 1985 one quarter of the animals in the 9-12 year old age group were pregnant. In all of the population simulations carried out in this study a mean fecundity of 0.25 has been assumed for mature animals and the age at first parturition has been spread across the age groups (Table 2b).

Age 38230 10 11 12 13 14 15 16 - 43 44 45 46 47 48 49 50
Fecundity 0 0.03 0.08 0.125 0.175 0.225 0.25 0.25 0.25 0.225 0.175 0.125 0.08 0.03 0
Table 2b: Age specific fecundity

Age at death has been assumed to be 50 years. Fecundities are unlikely to vary much amongst the Namibian elephant subpopulations. It is possible that, under the harsh arid conditions of Damaraland and Kaokoland fecundities may be lowered in times of nutritional stress but (a) this factor is likely to be secondary to natural mortality and, (b), the 'desert-dwelling' elephants are part of the same population as the Etosha elephants (Lindeque 1988).