Demography - Sperrgebiet Brown Hyenas

The Brown Hyena Research Project managed to fill many gaps between study areas and we are in the process of being able to look at the Sperrgebiet brown hyena population in total. This will have major conservation impacts. For example, our data indicates that the distribution of permanent and periodic water sources is more important to brown hyenas than previously suggested by other researchers. Furthermore, brown hyenas occupying territories in inland areas of the Sperrgebiet also make use of the coast on regular excursions out of their territory, with travelling distances reaching more than 50 km to reach the coastal food sources.

After establishing baseline information about brown hyena occurrence, abundance, home range size and habitat use in the Sperrgebiet, we will be able to look into other ecological fields by expanding research into interspecific relationships between brown hyenas and their prey species (herbivores) and competitors (e.g. spotted hyena, leopard, black-backed jackal).

Furthermore, we have established the first genetic profile of Namibian brown hyenas and by expanding the study area to cover the entire Sperrgebiet, we will be able to obtain data to detect the populations� viability, to determine relatedness between clan members and clans and to identify movement between populations. The basic aim of this study is to combine all previous and on-going data and to fill the necessary gaps in knowledge and data.

The Ministry of Environment and Tourism (MET) has recognised that the coastal Namib brown hyena population is ecologically unique and supports further studies to determine the conservation status in Namibia and to manage the population effectively (Griffin, pers. comm.). Since the commencement of our studies in 1997, we detected the limitations and adaptabilities of brown hyenas in the coastal areas of the Sperrgebiet. It is clear, that, although seals are an abundant and permanent food source, the brown hyena population is limited by other factors than food availability and quality. Intra- and interspecific competition, habitat limitations and the general clan structure seems to influence its population growth. Further studies in this unique ecosystem are necessary to widen the knowledge and to reach the MET�s aims.

Processes within ecosystems and between ecosystems (e. g. Atlantic Ocean and Namib desert food web) are complex and one can only gain an understanding by looking at the species that co-inhabit an area as a whole. This is an ultimate goal, which is rather impossible to reach. Nevertheless, indicator or flagship species, such as carnivores that have a high position in the food chain, are often good indicators for the stability and health of an ecosystem and by studying parts of food webs and interspecific interactions one can gain information about other trophic levels and relationships as well. The brown hyena has been declared a flagship species for the Sperrgebiet National Park and a first draft of the monitoring programme has been developed. The monitoring of the brown hyena population in the Sperrgebiet will not only provide information about changes in the terrestrial ecosystem but also indicate changes in the marine ecosystem.

 

The figure below illustrates the rationale behind this study. The following relationships are important for the understanding of the ecotone and its habitats and the resulting aims of this study:

  • Ocean: seals breed and reproduce on land, but as a top marine predator, their food web is linked to the ocean
  • Coast: In this area marine food subsidies, including seals, are available for brown hyenas and jackals. Other large to medium sized carnivores don�t occur in this area
  • Desert 1 : The brown hyena is possibly the only large carnivore in this area
  • Desert 2 : Several large carnivore species exist in this area
  • Farmland: Carnivores, humans and livestock are found in this area


1. Coast: Brown hyenas and black-backed jackals both feed on seals and compete for this food source. Seal breeding colonies on the mainland serve as a permanent and localised food source and hence, an influence on brown hyena abundance, home range size, activity and habitat use is expected.

2. Desert 1: Brown hyenas and jackals both feed on herbivore carcasses, but abundance of both species is expected to be lower than along the coast, hence competition is smaller. However, first results show that brown hyenas occupying territories in this area visit the coast to supplement their diet. Their movement also indicates a relationship with the availability of water. Whether the water sources itself or the movement of their prey species in the relation to the annual rainfall influences brown hyena behaviour and activity is an important part of this study.

3. Desert 2: Brown hyenas co-occur with other large carnivores that feed on the same food sources. Competition can be large, but carnivores such as spotted hyenas and leopards could also have a positive impact on the brown hyena population through providing additional food, such as leftovers of kills.

4. Farmland: Human-wildlife conflict exists with all large carnivores and might influence their abundance.

 


Longitudinal distribution of different areas in the Sperrgebiet and simple food web indication
(solid arrows � feeding, dashed arrows � interspecific competition)

 

The overall aim therefore is to investigate the brown hyena food web including interspecific competition in the Sperrgebiet and buffer zone.