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).
|
