Monitoring deaths and disease

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Chapter 2 STUDY SITES

Sterkfontein Dam Nature Reserve

The majority of the study was conducted at Sterkfontein Dam Nature Reserve (hereafter Sterkfontein) (S 28° 24’, E 29° 02’), situated approximately 20 km south-west of the town of Harrismith in the eastern Free State of South Africa (Figure 2). It has a total area of 17770 ha, of which 6940 ha are covered by water when the dam is full. Altitudes vary from 1 700 m around the dam to 2325 m in the hills at the south end of the Reserve. Sterkfontein has a mild climate with summer rainfall (Figure 3). Extreme maximum and minimum temperatures recorded are 38° C and -11° C respectively with an overall average of 17° C. Annual rainfall averages 680 mm in the northern part of the Reserve, but may reach 1400 mm on the high ground of the south. Occasional snow and frequent burning have a major influence on the vegetation.
Sterkfontein is a relatively new Provincial Nature Reserve and was created as a result of the dam construction. In the early 1960’s it was determined that the capacity of the Vaal Dam would not be sufficient to cater for the water needs of the Gauteng region. As a result, the Tugela-Vaal scheme was developed to pump water from the Tugela River via the Sterkfontein Dam to the Vaal Dam. Sterkfontein Dam was to act as a reservoir for the Gauteng industrial area. The Dam, a joint project of the Department of Water Affairs and Escom, was completed in 1986 and is included in the international register of the world’s largest dams. On completion it was the world’s second largest earth wall and the largest without a spillway. The Dam and land area around it, owned by the Department of Water Affairs, was mandated to the Free State Conservation Department and proclaimed a Provincial Nature Reserve in 1989.
Sterkfontein falls within the Grassland Biome, and has been split into two vegetation types: Moist Cool Highveld Grassland in the north (Bredenkamp & van Rooyen, 1996) and Wet Cold Highveld Grassland in the south (Bredenkamp, van Rooyen & Granger, 1996). In pristine condition, the former is dominated by Themeda triandra, with other grass species encountered including Eragrostis superba, Brachiaria serrata, Heteropogon contortus, Cymbopogon plurinodus, Setaria sphacelata and Tristachya leucothrix. There are many dicotyledonous forbs including Tephrosia semiglabra, Ipomoea obscura, Sutera atropurpurea, Helichrysum spp., Crabbea acaulis, Hermannia depressa and Rhynchosia totta. Deep, red (Hutton) and yellow (Clovelly) soils occur mostly on Karoo Sequence sediments but also on shale (Witwatersrand Supergroup) and andesitic lava (Ventersdorp Supergroup).
Structurally, Wet Cold Highveld Grassland is grassland, but a woody layer between 3 and 5 m may form dense thickets in places. This woody layer comprises Leucosidea sericea, Euclea undulata, Diospyros whyteana, Myrsine africana and Rhus dentata. North facing slopes are dry and poor in grass species, being dominated by Hyparrhenia hirta and Aristida diffusa. Other grass species include T. triandra, Eragrostis curvula, C. plurinodus and T. leucothrix. South facing slopes are relatively moist, where species rich, dense thickets with a sparse undergrowth are dominated by a non-grassy herbaceous layer. Characteristic species are the grass Poa annua, and forbs Sutera polelensis, Stachys kuntzei and Clematis oweniae. This is mountain grassland, with the typical cool, wet Drakensburg montane climate and severe frost. Soils, typical of a mountain landscape, are shallow lithosols, mainly representative of the Glenrosa and Mispah soil forms. Sandstones and mudstones of the Elliot and Molteno Formations (Karoo Sequences) and the Beaufort Group are predominant rock types.
The main study site comprised an area of 550 ha in the north-eastern sector of Sterkfontein, between the main wall and small eastern wall (Figure 2). The area was enclosed on three sides by 2.4 m high game fencing and the remaining boundary was set by the water level of the dam. The populations were, therefore, self-contained with limited influx of new genetic material. The average annual rainfall during the study was 682 mm (Figure 3c), and altitudes varied between 1700 m and 1900 m. Within this area all population studies, behavioural studies and home range investigations were conducted. Also, in May and August 2001, two culls removed 12 mountain reedbuck, and a further two animals were collected in February 2002.
The land on the northern boundary of the study area belonged to the Department of Water Affairs. It formed steep hillsides and contained herds of grey rhebok and mountain reedbuck at densities thought to be similar to those on the side of Sterkfontein (pers. obs.). The land adjacent to the north-eastern boundary was used for commercial cattle grazing, where there were relatively low densities of grey rhebok and mountain reedbuck (pers. obs.), while that to the east was used for arable crops. There was no game on this area.
South of the main study area was a separate section of Sterkfontein, which formed the second but less extensively used study site. Although adjacent to the main study area, it was isolated from it by a game fence. This second site was situated on the south side of the small eastern wall (Figure 2) and comprised an area of approx 800 ha. Weather conditions and altitudes were very similar to those of the main study area. This section was used for culling mountain reedbuck, and between March and December 2000 four culls removed 20 animals. A further five animals were collected from this area in November 2001 and February 2002.

Tussen die Riviere Nature Reserve

Tussen die Riviere Nature Reserve (hereafter TdR) (S 30° 30’, E 26° 07’) is situated approximately 20 km east of the town of Bethulie in the southern Free State of South Africa (Figure 4), at the confluence of the Gariep (formerly Orange) and Caledon Rivers. The total area of the reserve is approximately 22 000 ha and the altitude varies between 1200 and 1500 m. The climate is defined as arid (steppe), cold and dry, with a mean average temperature of 18° C (Werger, 1973). Annual rainfall averages 420 per year (Figure 5). TdR falls in the Eastern Mixed Nama Karoo, part of the Nama Karoo Biome (Hoffman, 1996), previously the False Upper Karoo (Acocks, 1988). Although this was considered the most degraded of all vegetation types in South Africa (Acocks, 1988), Werger (1973) recorded a marked recovery of the veld after the withdrawal of farming and the creation of TdR in 1967.
TdR has a complex mix of grass and shrub dominated vegetation types. Common shrubs include Pentzia incana, Eriocephalus ericoides, E. spinescens and Hermannia spp., while dominant grass species include Aristida spp., Eragrostis spp. and Themeda triandra. Tree species, including Acacia karoo and Celtis africana, are commonly found along the rivers, but are not abundant elsewhere. Beaufort Group sandstones and shales dominate the landscape, with the flat-topped landscape shaped by many dolerite dykes and sills.
Mountain reedbuck are regularly hunted and culled at TdR and biological material was obtained from 41 animals collected between December 1999 and June 2001. No observations were made on live mountain reedbuck at TdR, while grey rhebok do not occur there.

POPULATION DYNAMICS

Introduction

Population dynamics is the study of temporal changes in the number and composition of individuals in a population, and the factors that influence those changes. It is important for successful management and conservation, and involves four basic components of interest to which all changes in populations can be related: births, deaths, immigration and emigration (Caughley & Sinclair, 1994).
Birth rates are affected by age at first reproduction, birthing intervals, average number of young produced, and the quality and quantity of food available when there are new lambs. The death rate is normally age-specific and sometimes sex-specific, and is related to survival and longevity. The mating system and degree of territoriality of a species, as well as the suitability of the surrounding habitat affect dispersal, which is the movement of an animal from its natal area of birth to a new area, where it breeds (Caughley & Sinclair, 1994). This is an understudied and poorly understood component of wildlife population dynamics but is critical to the long-term persistence of a species. Sex ratios, mating systems and age structures also affect how many animals within a population are able to breed.
Some of the basic components of population dynamics have been described for grey rhebok (Esser, 1973; Ferreira, 1983; Beukes, 1984, 1988; Rowe-Rowe, 1994). This antelope either forms social herds in which an adult male maintains a small harem of between two and five females as well as the young born that year, or males remain solitary (Ferreira, 1983). In the former, the mating system is female defence polygyny, while solitary males do not get the opportunity to mate. Also, because one male sires offspring with more than one female, there is strong competition amongst males for females. Groups containing up to 10 females may occur, but larger herds are rare, and temporary aggregations of two groups are only likely to occur if one male is absent. This is because territoriality is very strong and males do not tolerate rivals within their home ranges (pers. obs.). Adult males without a harem do not generally form bachelor herds, although yearling males may form temporary associations after they have been evicted from their natal groups. Grey rhebok are seasonal breeders, with females producing a single lamb between November and January in the Free State and Kwa-Zulu Natal (Ferreira, 1983; Rowe-Rowe, 1994) and during August in the Western Cape (Beukes, 1984). Little has been recorded about the age at first reproduction and birthing intervals, while death rates (Oliver, Short & Hanks, 1978) and dispersal (Esser, 1973) have not been well investigated. For the latter, young males leave their natal herds just before new lambs are born.
The population dynamics of mountain reedbuck in the Karoo, South Africa have been covered comprehensively by Norton (1989). Social organisation consists of territorial males, non-territorial males, herds of females with young, and bachelor groups (Irby, 1976). Female herds normally consist of small groups of 3 – 8 individuals, but congregations of over 30 animals may occur under certain circumstances (pers. obs.). All female groups are unstable, with females and young moving from herd to herd (Irby, 1976). The mating system is resource defence polygyny. Territorial males occupy their territories all year while females move from one male’s territory to another. These males generally do most of the breeding (Irby, 1976), but have no control of females once they move out of the males’ territories. There is then a greater chance for opportunistic mating by non-territorial male mountain reedbuck than for solitary male grey rhebok. Although mountain reedbuck are considered aseasonal breeders and single lambs may be born at any time of year, there is a distinct birth peak between November and January in South Africa (Irby, 1979; Norton, 1989). Age at first reproduction in females is approximately 15 months (Irby, 1979; Norton, 1989) while birthing intervals are eight months to one year. Mortality rates are relatively high in juvenile animals, particularly immature males, low in young and middle age classes (with no differences between sexes), and relatively high again in older age classes ≥ 7.5 years. Adult sex ratios vary from 1 M: 1.64 F to 1 M: 3.3 F (Irby, 1979; Norton, 1989). Young males are evicted from their natal areas between nine and 15 months age.

CHAPTER 1. INTRODUCTION
AIMS
CHAPTER 2. STUDY SITES
Sterkfontein Dam Nature Reserve
Tussen die Riviere Nature Reserve
CHAPTER 3. POPULATION DYNAMICS 
Introduction
Method
Study site and animals
Changes in population size
Monitoring deaths and disease
Result
Births.
Deaths
Discussion
Births.
Deaths
Translocations
Aerial counts
Overall trends
CHAPTER 4. HOME RANGES AND HABITAT
Introduction
Study site and animals
Geographic positions ..
Statistical methods
Accumulative home range area graphs ome ranges areas
Ecological densities
Home range areas
Vegetation surveys
Interspecific comparison of home range size
CHAPTER 5. ACTIVITY PATTERNS, FORAGING BEHAVIOUR AND SOCIAL BEHAVIOUR
Introduction
Methods
Study site and animals
Behaviour
Activity budgets and activity patterns
Territorial marking
Statistical methods
Results
Discussion
CHAPTER 6. BODY CONDITION
Introduction
Methods
Results
Discussion
CHAPTER 7. PARASITES
Introduction
Methods
Results
Discussion
CONCLUSIONS
SUMMARY
REFERENCES 
APPENDIX
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