Researcher: Werner Killian and Dr.Conrad BrainRegion: Kunene Region & Etosha National Park, Namibia
BackgroundThe aim of the project is to understand how ecological factors regulate or limit elephant population numbers in Etosha and western Kunene in north-western Namibia.
- To assess differences in the age structure (demography) of elephants within Etosha and Kunene;
- To assess the seasonality of calving rates, timing of births, and recruitment within Etosha and Kunene;
- To assess the impact of environmental variability, including disease, on the demography of the elephant populations.
The factors that explain changes in population size are a central theme in ecology. Long-term studies of population dynamics are of great importance and have significant consequences for wildlife management and conservation biology. Data on elephant population trends in Etosha have been collected since 1972 and can be characterised by three phases:
- An expansion phase where the numbers of elephants increased rapidly through immigration and recruitment;
- A period of decline with culling and an increased incidence of anthrax and
- A subsequent phase of population stabilization.
Although it has been suggested that anthrax is the major factor responsible for the stabilisation of the elephant numbers in Etosha, this remains speculation and no definitive data has been collected to substantiate this. The stabilisation phase is rare and has not been described in elephant population elsewhere in Africa. This makes Etosha the ideal site to study the processes affecting the population dynamics of elephants. The inclusion of anthrax as a strong regulating factor in large mammal population dynamics is a novel concept, with implications for management on a far larger scale than Etosha
MethodologyAn effective way in which to illustrate population regulation is through demographic studies. Elephants are particularly suited to these types of studies, because age classes are readily identifiable.
The demography of the breeding herds of elephant will be assessed by aerial photogrammetry, a method that consists of photographing elephant breeding herds vertically. The best run for each herd is selected and printed out. From this print-out, the length of each elephant is measured with vernier callipers. These lengths are then expressed as a fraction of the length of the biggest female in the herd and distributed into appropriate age classes by applying the mean growth curve.
Aerial photogrammetry provides a rapid assessment of the age structure of the elephants. The age structure is then used to provide an indicator of the potential of the population to increase; do comparisons between populations; and determine the timing or phenology of births.
The aerial photogrammetry will be supplemented by regular monitoring of known breeding herds during ground surveys. If done repeatedly, it is then possible to determine seasonal recruitment and age specific mortality. The data will then be used to improve our knowledge of the importance of population regulation in the elephant populations under study.
To adequately describe and compare the response of elephants regulating mechanisms to variation in rainfall and disease, the age structure of elephants will be assessed in three areas:
- north-eastern sandveld of Etosha,
- area west of the dolomite hills in western Etosha, and
- areas containing the breeding herds of the ephemeral river systems in Kunene.
- These areas are characterised by differences in local rainfall, incidence of disease and human impact.
The aerial photogrammetry of elephant herds will be conducted 3 times a year for 3 years, during the hot period e.g. August, September, and October. Upon the conclusion of each flight, the analysis and dispersal of data will commence.
Annual Report 2011
With over a thousand elephants now photographed from the air for demographic purposes this project is in its final phase. Namibian elephant herds from Kaudum westwards have been photographed from the air and age determination of these herds is nearing completion. The challenge for this past year has been to record as many elephants as possible in the arid north-western regions of Namibia.
Elephants in this region are particularly difficult to find, but by combining our efforts with other aerial operations in the area, we have been particularly successful in recording the animals without spending huge amounts on aircraft hire in searching for these elusive herds. This approach has inevitably prolonged the project as to allow us to make use of helicopter and aircraft time as other opportunities presented. The actual measurements of the elephants for age determination are being undertaken at the Etosha Ecological Institute and the University of California Berkley.
Determination of mortality factors amongst these elephants has remained a focus to assess the influence of anthrax on the elephant herds along an east-west gradient across Namibia. To compliment this project, 21 elephants in the north-west were collared with GPS transmitters which will allow for accurate follow-up on select herds and provide accurate movement data of these elephants.
March 2010 Update
During the past year, aerial photogrammetry of elephant herds was conducted at several localities in Namibia including Etosha, Kaudum, and the Kunene. These areas are characterised by differences in local rainfall, incidence of disease and human impact and can thus be used to adequately describe and compare the response of the elephants’ regulating mechanisms to variation in rainfall and disease.
Where possible, post-mortem examinations were also carried out on elephant and cause of death noted. Results from these post-mortems together with photogrammetry-determined demographic data are under analysis. Preliminary data analyses show significant differences in recruitment in the respective areas.
The assessment of the age structure of elephants in Etosha was done by means of fixed-wing and helicopter surveys across the entire Park from west to east. This provided a sample size in excess of 600 elephants, which is representative of approximately 25% of the estimated number of elephants in Etosha. A helicopter survey of Kaudum and the Nyae Nyae Conservancy provided a sample size in excess of 1 500 elephants, which represents approximately 50% of the estimated elephant population in this area. A dedicated helicopter survey of elephant numbers and demography of the ephemeral river systems and adjacent areas of the Kunene Region provided a sample size in excess of 200 elephants.