Territoriality and spatial patterns of white rhinoceros in Matobo National Park, Zimbabwe

1. What they did

Most African rhinos today live in fenced sanctuaries or reserves because of poaching. Fences stop young animals moving away, so numbers inside can build up. The authors asked how this, together with population density and behaviour, affects the way adult male and female white rhinos use space.

They studied white rhinos in Matobo National Park, Zimbabwe, in 1994 and 1995. Most of the 52 rhinos lived inside the fenced Whovi Game Park at high density; a group of nine lived outside the fence in the Hazelside Area at lower density.

• Identifying and locating rhinos. All adults and most subadults were known individually by their ear-notch patterns. Sixteen adults wore radio collars and were located at least once a week. Other rhinos were found by sight or by following their spoor with a National Parks tracker. Locations were taken from a topographic map and/or a handheld Global Positioning System (GPS).
• Home ranges. Using one location per day per animal, they estimated the areas each adult used, with the minimum convex polygon (MCP) and adaptive kernel (ADK) methods, and measured how much the ranges overlapped.
• Behaviour. They watched rhinos in daylight, mostly early morning and late afternoon, recorded what each group was doing every 5 minutes, and recorded every act of male scent marking.

2. What they found

Territorial and non-territorial males

• Territorial males marked with two distinctive behaviours: scattering dung with vigorous kicks of the rear legs before and after defecating, and spraying urine backwards in 2 to 5 pulses, often after scraping the rear legs along the ground or over vegetation. They did this at a mean rate of 3.0 acts per active hour.
• Non-territorial males urinated in a stream like females and did not scatter their dung. Four young adult males (6 to 10 years old) started marking, but only now and then and less vigorously.
• Territories were very large: 1462 to 5041 ha. The largest territory reported before for a white rhino male was 1390 ha, smaller than the smallest territory in this study.
• Only three males inside the fence held territories at first. When one territorial male (M-07) was killed in a fight with a neighbour, two neighbouring males took over parts of the empty area. One of them (M-25) had started marking about 2 months earlier at the edges of two territories but kept to a small area until then. The number of territories did not increase.
• Males expanding their territories marked about five times more often (M-09: 0.36 to 1.98 acts per active hour; M-25: 1.32 to 6.42). The male who did not expand did not increase his marking.
• Territories hardly overlapped each other (9.4% before the shift, 0.1% after). The eight non-territorial males used similar-sized ranges that overlapped widely (26.8%), significantly more than territorial males overlapped. Territorial and non-territorial males also overlapped a lot (29.2% and 24.4%).
• Unlike other populations, no territory was shared by a dominant “alpha” male and a subordinate “beta” male. Pairs of non-territorial males tended to stay together for several months.

Females

• Females in the high-density fenced area used home ranges averaging 1901 ha (95% ADK). Females in the low-density Hazelside Area used significantly larger ranges, averaging 5890 ha.
• Female ranges overlapped widely in both groups. Each female inside the fence shared parts of her range with at least five other adult females (7.4 on average), with a mean overlap of 40%.

3. What they concluded

• Scent marking is a useful way to tell territorial from non-territorial males by how they use space.
• Only one third of adult males inside the fence held territories, compared with up to two thirds in other populations. Three factors may explain this: very large territories (possibly because so much of the park is rocky and unused by rhinos), the fence stopping young males moving out to set up territories on the edges, and a young male age structure after older males were removed in the mid-1980s.
• The result was that a few males held territories covering most of the space. Other males faced the “choice” of challenging a territory holder, at the risk of injury or death, or following a non-territorial pattern. Only territorial males are believed to breed successfully.
• Females in the lower-density group used larger ranges in similar habitat, suggesting females change how they use space in response to population density. High overlap in both groups suggests shared resources or social factors also shape where females live.

4. How tracking was or was not used

Tracking played a supporting role. Rhinos without radio collars were located either by sight or by following their spoor with the help of a National Parks tracker. The paper does not say how many locations came from following spoor. Scent marking (dung scattering and spray urination) was recorded by direct observation of the behaviour, not from the signs left behind.

5. Tracker or observer certification

Not reported. The National Parks tracker is not named and no experience, certification or test of skill is described.

6. Other technologies, skills or innovations

• Radio collars on 16 adults, and individual identification of all adults and most subadults from ear notches.
• Handheld GPS and 1:50 000 topographic maps for recording locations in Universal Transverse Mercator (UTM) co-ordinates.
• The CALHOME home range analysis program and the IDRISI geographic information system (GIS) for home ranges and overlap.

7. Implications for conservation (from the paper)

• Protection within reserves is likely the most viable way to conserve rhinos where they live, but smaller reserves may need management to make up for restricted dispersal.
• With no dispersal, managers may need to regulate the number of males, the sex ratio and the total population size within fenced areas.
• Managers of smaller reserves should monitor the territorial behaviour and spatial patterns of adult males, so decisions are made with an understanding of male behaviour and territorial status.