By Ingrid Wiesel, PhD student at Hamburg University, Germany, based in Lüderitz
Brown hyaena (Hyaena brunnea, Thunberg, 1820) in Southern Africa are known to be mainly scavengers. They are also known to kill new-born seal pups at the mainland Cape fur seal (Arctocephalus pusillus pusillus) colonies along the Namib Desert coast, a predator-prey system that is still young and dynamic.
Main aspects of a current study on the Namib’s brown hyaena are not only the animal’s population and feeding ecology, but also determining the influence of hyaena predation on the population dynamics of the seals, and the importance of the mainland seal colonies for the size of hyaena populations.
Territory and home range sizes have to be determined, taking into account the hyaena’s dependency on the existence of seal colonies and their annual yield of seal pups. The methods used are direct observations, carcass and faeces analysis and radio tracking in four different sample areas representative of the entire coast line. At the end of this long-term study (1998 – 2000) it should be possible to calculate the population size of brown hyaenas in the entire Namib Desert, in addition to accumulating knowledge of their space and resource requirements.
Stability in predator-prey systems
The foraging efficiency of predators is determined by studying the prey species and their foraging strategy. Apart from this, real foraging behaviour represents a compromise between optimal foraging and activities such as territorial fighting and competitive behaviour.
In predator-prey-systems the efficiency of the predator determines the stability of the system. Ideally the predator should use its prey with minor additional impact on non-violent mortality. Research has shown that most existing predator-prey-systems tend to be stable, due to “judicious” hunting and the evolutionary advantage of the prey species.
All carnivores live in different but complex societies where communal hunting is not the basis for sociality, and does not help preservation of the species. Next to predators are scavengers, who live mainly off carcasses and prey killed by other predators. Nevertheless, scavengers such as black-backed jackals, Canis mesomelas, and brown hyaenas are able to hunt. This often occurs in areas with a low predator density, low pressure due to competitors and low availability of carcasses.
In the past brown hyaena have been studied mainly in the southern and central Kalahari Desert. In these long-term studies brown hyaena were found to be efficient scavengers which seldom hunt for small mammals, birds, reptiles and insects. Their hunting success lies between 5.7% and 13.7%. Territory size depends on the distance between meals, whereas group size varies with the number of food resources.
Long-term studies on the feeding ecology of brown hyaena at the Namib Desert coast are yet to be carried out. The results of a preliminary study in 1995 showed that brown hyaena fed predominately on Cape fur seal pups, observations that have been made by several researchers. The feeding ecology and behavioural biology of brown hyaena at the Wolf Bay seal colony were studied during 1998. Despite a huge food availability of dead seal pups killed by hyaena, the cumulative predation effect on seal pup mortality was 7.11%.
The mainland Cape fur seal colonies are historically very young. For example, the formation of the Wolf Bay seal colony happened around 1948. For this reason the predator-prey system between hyaenas and seals is young and still dynamic. It is, therefore, important to study this system in respect to evolutionary questions.
The key questions in the study of the ecology and behaviour of brown hyaena along the Namib Desert coast are:
This article appeared in the 2001 edition of Conservation and the Environment in Namibia.