| Numbers in Zimbabwe
- Numbers in Zambia - Numbers
Figure 17: Botswana elephant estimates
|Rate of growth %
Table 4c: Botswana elephant population estimates.
Dry season estimates rounded to nearest 1,000 animals.
In 2003 the northern Botswana elephant population was estimated
at 123,000 animals (Chase & Griffin 2003; Table 4c). A crude
best-fit model for the population suggests that it reached
its present level by increasing at a rate of 6.6% from a population
of about 8,000 animals in 1960 (Figure
This apparent growth rate raises interesting questions. If
immigration into the population is ruled out the question
arises whether an elephant population is capable of such a
growth rate. With a fecundity
of 0.25 and a central
mortality of zero, a population
model based on a stable age structure suggests a growth rate
of 5.7%. Increasing fecundity to 0.33 (i.e. adult females
produce one calf every 3 years) with a central mortality of
0.25 (which is about as low as one might reasonably hypothesize)
still does not result in a growth rate as high as 6.6%.
If survey techniques had improved over the time span of the
estimates this would provide one possible explanation. However,
this seems unlikely: from 1993 onwards the standardised techniques
of ULG (1995) have been used in all surveys. A model with
a starting population of 47,600 animals in 1987 gives a best
fit for the years from 1993 onwards with a growth rate of
If immigration were responsible for the high growth rate
it would have had to come from Zimbabwe - the Zambian and
Angolan populations were already depressed by 1987. Whilst
this is theoretically possible, it is unlikely. Martin (1992b)
showed that immigration from Botswana was necessary to explain
the high growth rates of the Zimbabwe population from 1980-1991.
Increased growth rate through skewed age structure
A growth rate of 6.6% can, however, be caused by a skewed
age structure for the population in combination with a reduced
central mortality and a slightly increased fecundity.Calef
(1988) detected the unusually high growth of the northern
Botswana elephant population but failed to recognise the importance
of a stable age structure in the population and attributed
the growth rate mainly to a very high fecundity. Using the
population model of Martin (2000b), a skewed age structure
was simulated by overhunting the adult male segment of the
age pyramid so that there were very few males older than 30
years in the population. With fecundity set at 0.28 (i.e some
12% higher than normal) and central mortality reduced to 0.1
% (which implies one natural death per year for every 1,000
animals between the ages of 5 and 45 years), when the hunting
quota is reduced to a sustainable level the population growth
rate immediately rises to a level of 6.6% and decreases slowly
over about 20 years as the population assumes a stable age
A skewed age structure is the most plausible explanation
for the history of population estimates. There is evidence
to suggest that prior to the inception of sustainable quotas
in the 1990s, the northern Botswana population had suffered
a long history of overhunting for trophy males both from citizen
hunting and international sport hunting. The absence of large
trophy animals in the population has been noted by numerous
observers (P. Becker, pers.comm., G.F.T. Child, pers.comm.,
I.S.C. Parker, pers. comm.).
If the population curve is projected to the year 2005, a
population over 150,000 animals is predicted. However, the
number of animals resident in Botswana is likely to be less
than this. Firstly, the population growth rate should by now
have decreased to under 5% as a result of achieving a stable
age structure. Secondly, there is evidence of emigration from
the population (Chase & Griffin 2004, Chase et al 2004, G.
Owen-Smith pers.comm. and population models for Caprivi and
Khaudum in this report).
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Figure 18: Zimbabwe elephant estimates
Table 4d: Zimbabwe elephant population estimates.
Zimbabwe elephant population model
The north-western elephant population in Zimbabwe has a record
of standardised sample surveys dating back to 1980. As the
elephant population has expanded into forest reserves, communal
lands and private farms in the last 15 years, the survey area
has increased slightly. However, it is unlikely that because
the new areas were not surveyed in the 1980s that the earlier
estimates were incomplete: 20 years ago there were very few
elephants outside Hwange National Park and the Matetsi Safari
Area. Rigorous annual surveys were carried out until 1995.
There have been no surveys since 2001.
Taking into account major culling operations in the 1980s,
two alternative methods of modelling the population both yield
the result that the population is increasing at a rate similar
to the Botswana elephant population (more than 6.5% per annum).
The explanation for this high rate of increase is likely to
be the same as for Botswana - only
with a highly skewed age distribution are such growth rates
The north-western elephant population suffered a high level
of problem animal control for perhaps 30 years prior to 1980
(D.H.M. Cumming pers.comm.). This could well have been responsible
for a population with a low number of adult males and the
necessary skewed age structure to produce the high growth
rates demonstrated by the population. From 1980 onwards there
was an increasing trend towards wildlife becoming the predominant
form of land use in Matabeleland North and this allowed the
expansion of the elephant population into Forest Areas, communal
lands and commercial farms. At the same time, sustainable
quotas for elephant sport hunting were being set. These two
factors acting together are likely to have produced the apparently
high growth rates.It is important to note that a high population
growth rate does not necessarily mean any increase in the
annual production of elephant calves. Without a stable age
distribution, it is simply an arithmetic artefact caused by
dividing the same crop of calves by a smaller adult population.
The combined effect of these two very large elephant populations
(northern Botswana: 150,000 animals; north-western Zimbabwe:
50,000 animals) has major implications for the management
of elephants in north-eastern Namibia.
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Elephant populations throughout Zambia were severely depleted
by a wave of illegal hunting which began in the late1970s.
Between 1981 and 1985 Zambia may have lost 100,000 elephants
(Martin 1986). Despite a hunting ban in 1981 and the listing
of the Zambian elephant population on Appendix I of CITES,
elephants continued to decline in most parts of Zambia. AfrESG
(1998) estimated the population as 15,873 animals ('definite'
estimate). The south-west corner of Zambia was not exempt
from this holocaust.
Chase (et al 2004) carried out a survey of Sioma Ngwezi National
Park and its immediate environs and estimated 1,212 elephants,
of which the majority were in the national park (1,099). The
authors remark that the population does not appear to have
increased since the last survey which estimated 1,187 elephants
in 1991 (Tembo 1995). They attribute the status quo to high
levels of illegal hunting, human settlement along the Kwando
River which is preventing Botswana's dispersing elephants
from reaching Sioma Ngwezi and to veterinary fences also constraining
DG (2004) shows a discontinuous elephant range in south-western
Zambia with no links between Sioma Ngwezi and the nearby Kafue
National Park. Recently large numbers of elephant are being
seen along the Zambezi from Livingstone westwards to the point
where the borders of Botswana, Namibia, Zambia and Zimbabwe
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The elephant population in Angola was heavily hunted during
the UNITA occupation of southern Angola after independence
in the 1970s and, although the civil war has ceased, wildlife
law enforcement continues to be problem due a lack of manpower
Chase & Griffin (2004) surveyed the Luiana Partial Reserve
in the south-east corner of Angola and estimated 372 elephants.
Most of the animals were within 50km of the Namibian border
and away from human settlements. Radio tracking studies have
shown movements of elephants from Botswana into the area despite
the presence of landmines. The authors stress the importance
of the Luiana Partial Reserve as a dispersal area for the
irrupting elephant population in Botswana.
The status of elephants in Iona National Park is uncertain.
They were present here in the 1970s but there are no recent
reports which confirm their presence or absence.