Aerial block count of black rhinos in Etosha National Park

(A version of this article was originally published in The Horn, spring 2010. Author: Pierre du Preez, Directorate Scientific Services, Ministry of Environment and Tourism)

In 2001, it was suggested that aerial block counting could potentially be used as a method for estimating black rhino numbers in Etosha National Park. As a result, an initial block count was held in 2002, followed by more intensive counts in 2003 and 2004. These counts formed a platform to design the 2005, 2007 and 2009 block counts.

A black rhino cow and calf, seen from the air, in Etosha National Park. Early mornings are good for aerial monitoring, as the air currents are still and the animals are still moving. As the heat increases, they'll find shade and go to sleepCredit: Ministry of Environment and Tourism

From 2003, a 4km x 4km grid system has been used to demarcate blocks within the Park. This systematic approach ensures that the unique grid numbers can always be used to cross reference the blocks counted. During a count, blocks are randomly selected and then each selected block is systematically flown until the recorder and observers are satisfied that all rhinos have been recorded, thereby ensuring that a total count has obtained for each block. The Ministry of Environment and Tourism decided to use a four-seater turbine helicopter to carry out the surveys. The required low flying combined with high altitudes and extreme weather conditions (which are particularly common in September and October) mean that helicopters are a much safer and more suitable choice than fixed-wing aircrafts.

Using the data collected and custom-made software, an estimate of the population can be calculated for the whole Park although this figure is kept confidential. It is also possible physically to land at all elephant and rhino carcasses to determine possible cause of death, collect soil samples for anthrax testing and collect tusks and horns.

The GPS localities of all sightings in each block are recorded and dependent calves are classed in age categories. Where possible, the observer behind the pilot takes digital images of all rhinos seen. Digital images assist greatly in individual recognition which minimises the risk of double counting and significantly improves the accuracy of the data that is collected.

The demographic data obtained on the surveys conducted since 2002 show that there is a small degree of variability between years and different areas and that the proportion of calves in the population has increased significantly. By reducing the number of unknown adult to a negligible figure, regular surveying has also facilitated far more accurate estimations of sex ratios.

The most recent block count in 2009 was highly successful and demonstrated that the black rhino population in Etosha National Park is healthy, growing and one of the most important black rhino populations within a protected area in Africa. The block count also contributed to the CITES MIKE (Monitoring Illegal Killing of Elephants) programme and the indications are that poaching is under control.

Reliable population size estimates and detailed demographic information on the black rhinos in Etosha are crucial for rhino translocations within Namibia, as Etosha is the major black rhino donor population for all introductions in Namibia.

Ongoing support from Opel Zoo

Opel Zoo, which gave 50,000 euros through the EAZA Rhino Campaign to support MET’s work over four years, has recently confirmed that it wishes to continue to support Namibia’s black rhinos with 5,000 euros a year. We’d like to thank Thomas Kauffels and his team for their wonderful commitment to in situ conservation.