Population Ecology

Desert environments such as the Namib Desert are difficult to access, which restricts the determination of movement patterns of far ranging predators. Brown hyenas are known to have vast home ranges of up to 461 km square (Mills 1990) and recent home range estimates in the Central Kalahari have shown, that individuals even use an area in access of 1000 km square (Maude pers. comm.).

The only home range estimates available for the Namib Desert of 107 km square and 220 km square were calculated in 1986 (Goss 1986) through radio tracking brown hyenas from a vehicle. The Brown Hyena Research Project has been radio tracking brown hyenas between the port of Lüderitz and Elisabeth Bay in the south since 1998. The limited network of roads, the strict ban of off-road driving and the fenced border of the Restricted Diamond Area known as Sperrgebiet (SPG) create a bias towards radio fixes, received close to existing roads.

In order to overcome these difficulties and resulting biases, we decided to combine vehicle tracking with aerial telemetry. Since the beginning of 2003 tracking flights are carried out approximately every three weeks, weather dependent, with the support of Sidewinder Films/Namibia Nature Foundation. We started to track three radio collared brown hyenas of two different clans and the success of the aerial tracking during the first year was great.

Up to date, eight brown hyenas are fitted with collars. These brown hyenas belong to four different clans, namely the Agate Beach/Anigab clan, Peninsula clan, Wolf Bay clan and E-Bay clan:

Agate Beach/Anigab clan: a male and a female brown hyena are radio collared. The area stretches from the port of Lüderitz up to north of the Anigab Pan. No mainland seal colonies occur in this area, but washed up seals are available.

Peninsula clan: two female brown hyena are fitted with collars. The area comprises of the Lü:deritz town lands and the Lü:deritz Peninsula. No mainland seal colonies exist in this area, but a good amount of herbivores, washed up seals, carrion and refuse from the towns rubbish dump.

Wolf Bay clan: a female and two male brown hyena are collared. A GPS collar of a male brown hyena was recovered recently. The area stretches from the bay Grosse Bucht just south of Lü:deritz to just north of E-Bay. Two mainland seal colonies exist in this area.

E-Bay clan: a female brown hyena carries a radio collar. The area stretches from Atlas Bay to south of E-Bay. Area possibly overlaps with Wolf Bay clan and therefore one mainland seal colony exists in this area.

From our previous years studies, we discovered, that all den sites close to the mainland seal colonies have not been used since the start of our research project in 1995, although they were apparently still used in 1992 (Wolhuter pers. comm.). We suspect, that home ranges of brown hyenas of different clans overlap greatly in areas with mainland seal colonies and that they moved their den sites, hence territory boundary, further away from the concentrated food source. Therefore instead of expecting small home ranges due to the superabundance of food for two of our studied clans, home ranges will be larger and possibly the same size than for brown hyenas of the Anigab clan. The study of this phenomenon is one of the major aims of the radio telemetry project, which is supported by Duke University and the Predator Conservation Trust.

We will also use GPS telemetry, but it is initially extremely cost extensive. The combination of vehicle and aerial telemetry cannot replace the results obtained through this technology, but will provide the same home range information just over a longer period of time.

Another approach to determine territory boundaries and size is known as “bait-marking”. Brown hyenas use latrines to defecate, but these latrines also serve for marking purposes. Latrines are scattered around the territory, but are found in higher numbers around den sites, feeding sites and territory boundaries. Bait is laced with indigestible plastic pellets and fed to the animals social group (preferably at a den). Each social group is fed with a unique coloured pellet and therefore the origin of the faeces can be assigned. This method has never been tried with large carnivores and is very time consuming. The preparation includes mapping of a large area to find latrines, then to find active den sites to be able to feed each social group with a different coloured marker.

So far, no brown hyenas have been fed with the marker. The first active den site in 2004 will serve as a pilot project and blue plastic markers will be fed to the brown hyenas of that particular social group over a period of three months. Theoretically blue marked faeces should only be found within the territory or home range of brown hyenas belonging to this social unit.

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