 Reference Base  A visit to the Nimule National Park in the Southern Sudan |
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Kock, D., 1961. A visit to the Nimule National Park in the Southern Sudan. African Wildlife 15 (4): 323-329, figs. 1-6
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| Location: |
Africa - Southern Africa - Zimbabwe |
| Subject: |
Management |
| Species: |
African Rhino Species |
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Abstract - In Zimbabwe, during the period 1991-1993, 478 immobilisations of both white (Ceratotherium simum simum)(n = 156) and black (Diceros bicornis)(n = 322) rhinoceroses were carried out. Of these, 360 animals were dehorned (white rhino, n = 136; black rhino, n = 224) as part of a management program to reduce the incentive to illegal hunters entering Zimbabwe from Zambia. Nineteen white rhino that were dehorned in 1991, were reimmobilised approximately 12 months after dehorning and horn regrowth measured and form of regrowth documented. A regrowth rate of 6,7 cm/ yr (n = 14) for the front horn and 2,9 cm/ yr (n = 14) for the back horn were noted. In the majority of rhinos, the shape of horns was roughly cylindrical after 1 year of horn removal. Several of the white rhino had abnormal regrowth characterized by central cavitation, partial cavitation with partial side wall collapse, and undercutting. None of these rhino exhibited ill health associated with horn abnormalities. Twenty eight black rhinos that were dehorned in 1992, were reimmobilised in 1993 for relocation purposes and attachment of telemetry devices. Regrowth (rate and form) was noted to be normal in all these animals except for some evidence of central splitting of the horn, but not into the germinal area. On occasion redehorning revealed a crescent shaped area of cavitation inside the horn. None of these showed evidence of moistness or discharge, nor invasion into the germinal area. The higher incidence of regrowth abnormalities seen in white rhinos was due to poor cutting techniques which damaged germinal epithelium. Improvements in cutting technique in 1 992/1 993 with black and white rhinos resulted in normal horn regrowth. Dehorning as a deterrent to illegal hunting has been successful in the black rhino, with only 19 animals killed during the period 1991-1993. This has been due to markedly improved law-enforcement, use of radiotracking and dehorning on a regular basis (every 1 2-1 8 months). The situation with the loss of > 80 white rhino in Hwange National Park in early 1993 was due to total lack of law enforcement and at least 18 months of horn regrowth. Dehorning is an effective conservation strategy, with little negative health or behaviourial effects on the rhinos but will only succeed if supported by aggressive law-enforcement.
INTRODUCTION
Protection of both black (Diceros bicornis) and white (Ceratotherium simum simum) rhinoceros in southern Africa since 1986 has consisted of improving law enforcement, increased intelligence gathering, capture and translocation of animals to safer areas to reduce losses due to illegal hunting.
In 1989, Namibia instituted a new strategy of dehorning selected populations of black rhinos due to an increase in illegal killing of this species, This technique, coupled with increased law enforcement proved effective in preventing further killing of black rhino in specific areas of the country.
In Zimbabwe, despite attempts to prevent illegal killing of both species of rhinos, through improved law enforcement and capture/ translocation, loss of rhinos proved to be unsustainable (with protection constrained by lack of adequate finances). A decision was made to carry out an experimental dehorning of white rhinos in Hwange National Park (HNP) in 1991, but continued heavy poaching resulted in a decision to dehorn all rhinos throughout Zimbabwe in an attempt to halt the decline.
Dehorning has proved to be a controversial management option, with both failures and successes with regard to reduced incentives for illegal poaching. The dehorning operations have allowed considerable data to be accumulated on its deterrent effect, rhino demography, immobilisations, horn size (before and after dehorning), horn regrowth, form of regrowth and veterinary-related problems.
METHODS
Details of immobilisation methods and data collected have been documented. In 1992, in conjunction with dehorning of black rhinos in HNP, the white rhino programme has allowed the collection of considerable data and allowed detailed evaluation of dehorning. During 1992 and 1993 dehorning of both black and white rhino continued in the Parks and Wildlife Estate and private Conservancies, and continues through 1994, combined with a major radio-collaring exercise.
RESULTS AND DISCUSSION
Numbers: During the period 1991-1993, over 478 immobilisations of both black (n =322) and white (n = 156) rhinoceroses were carried out. Of these, 360 animals were dehorned (white rhino, n = 136; black rhino, n = 224) as part of a management program to reduce the incentive to illegal hunters from Zambia (Table 1).
Research and Monitoring Program: A research and monitoring program was initiated in 1991 prior to starting horn removal on the white rhino in HNP. The aims of this program are:
(c) to document rates and form of horn regrowth,
(d) to gather information regarding poaching activity and rhino survival to assist in evaluation of the effectiveness of horn removal in lowering poaching risk,
(e) to investigate intra- and inter-specific behavioral interactions of dehorned rhino,
(f) to examine natural variation in horn and body sizes as they relate to dominance and reproductive performance.
Horn Regrowth: rates and form. Linear rates of horn re-growth were measured for white rhino adults immobilised in 1992, ca one year after horn removal (see Table 2 for measurements after dehorning, Table 3 for regrowth measurements). Average regrowth rates for adults did not differ significantly between the sexes for either anterior (males: n = 7, x = 6,8 cm/yr; females: n = 7, x = 7,0 cm/yr) or posterior horns (males: x = 3,4 cm/yr, females: x = 2,5 cm/yr). Rates of regrowth for all adults (n = 14) differed significantly between anterior (x = 6,7 cm/yr) and posterior (x = 2,9 cm/yr) horns. Thus, total horn regrown by white rhino adults averaged 9,6 cm/yr. Berger reported mean rates of regrowth (summed for both horns) for desert black rhinos in Namibia as 8,7 cm/yr and 13,3 cm/yr for adults and juveniles, respectively; no significant differences were detected between the sexes. Although we observed some evidence of rubbing of horn bases one year after horn removal in white rhinos, most horn wear was restricted to the lateral surfaces. Therefore, measured changes in horn length closely reflect rates of horn regrowth. Data are presented for black rhinos (Table 4).
The key measure of interest in horn regrowth is the mass and, hence, monetary value of the horns. Converting measurements into mass values, we found that adult males (n = 38) carried an average mass of 6,24 kg while females (n = 45) supported 5,10 kg before horn removal. Over 90% of the horn was removed from adult males and over 93% from females. Based on regrowth measured in the first year, mean annual mass produced by adults is 0,56 kg and 0,45 kg for males and females, respectively. The shape of horns one year following horn removal was roughly cylindrical. Horn wear has begun to produce a more conical shape to the horns of black rhino 3 to 4 years after dehorning (Berger, pers. comm.). Some white rhino immobilized 10-13 months later exhibited slight abnormality in the shape of regrowth at the base .
Dehorning Tools and Procedure: Retrospective evaluation of horn cutting technique
Normal horn regrowth: Nineteen white rhino were re-immobilised in HNP to measure horn regrowth and evaluate form of regrowth. Normal regrowth was roughly cylindrical but evidence of cracking was seen in several horns. This normal regrowth was related to the correct cutting technique with the chainsaw during dehorning. Evidence of rubbing and shaping of horns was present.
Abnormal regrowth: This was evaluated and defined by developing 4 categories of scoring for regrowth:
Score 1 was normal regrowth.
Score 2 was abnormal regrowth with central cavitation, with outer walls intact, occasionally with a central plug.
Score 3 was partial cavitation with incomplete walls.
Score 4 was undercutting with top of the horn intact.
These abnormalities appeared to be directly related to cutting technique and exposure of the germinal area at the base of the horn. For the development of abnormal horn regrowth scored as 2, the sequence of events are likely as follows: exposure of the germinal area results in infection, introduced either by rubbing or mud. This focus of infection, which cannot drain due to the presence of solid horn on the outside, results in the development of a cavity or failure of horn regrowth centrally.
None of the regrowth abnormalities appeared to have affected the health of the rhino. In fact, in many instances, scar tissue was present with evidence of normal horn underneath. With these abnormalities it appears that normal horn regrowth would be achieved in time, but further monitoring needs to be carried out. Radio-collars were placed on some adult white rhino with abnormal horn regrowth.
The correct cutting technique for dehorning must involve initial cuts ca 6cm above the base of the horn. These can be angled or horizontal. The chainsaw blade should then be used to shave the horn to conform as close to the skull as possible. The shaving should be stopped as soon as droplets of blood appear centrally but the area must be solid when pressurised by a finger. Shaving further will result in exposure of the germinal area.
CONCLUSIONS
Mortalities associated with dehorning
With improvements in technique and drug combinations used to chemically immobilise white and black rhinos, based on data collected in Zimbabwe during the period 1991-1993 (> 300 individual rhino immobilisations), the overall mortality rate for a dehorning operation will probably be < 2%. The mortality rate for white rhino immobilisations (associated with prolonged recumbency) will be < 3,5 %, and black rhino immobilisations < 1 %. It is likely, over time, that the overall mortality rate will approach < 1 %, especially for white rhinos.
Cost of dehorning
The cost of a dehorning exercise (with full complement of helicopter and aircraft) appears to have a direct relationship to the density of the rhino population, and the experience of the dehorning team. A low density rhino population will result in an escalation of costs due to difficulties in locating animals (even with ground tracking, fixed-wing support is necessary and judicious use of the helicopter essential). When a helicopter and fixed-wing are used in an operation, costs will tend to escalate. The most cost effective operations will be those carried out entirely on the ground, with only tracker support but time constraints would be a major limiting factor. This type of operation would apply to small, known populations in confined areas. Dehorning cost per animal have varied between US$350-18004.
Effectiveness as an Anti-Poaching Measure and Law Enforcement
Early in the dehorning program only eight dehorned white rhino were killed by poachers (known deaths) in the first 22 months. The number of incursions into HNP tripled in 1992, but the number of rhinos killed dropped from 2.0 to 0.5 per incursion. There were no incursions in 8 months in Matusadona National Park, following dehorning. Nineteen dehorned black rhinos are known to have died from poacher's bullets throughout the country up to the end of 1993, with two dying from other causes, in the space of 18 months. Contrast this with the 52 horned rhino that died between September 1991 and January 1992 (a 4-month period), throughout Zimbabwe, and an estimated loss rate of > 1 00 per year.
There are several important facts and observations that have become apparent with the Zimbabwe dehorning program:
1 . Dehorning must be accompanied by an aggressive law-enforcement programme,
2. Behaviourial effects appear to be minimal, and in contrast to a recent report several calves that were < 2 months old at the dehorning of their mothers have survived beyond 12 months in a predator-rich area. Dehorned black rhino have bred successfully and given birth, with one calf alive 4 months after birth.
3. Dehorning, if carried out by professionally trained individuals, has little effect on health, and the mortality rate should be less than 1 %.
4. The deterrent effect of dehorning has taken at least 12 months to show signs of effect. There is evidence that Zambian poachers are still being paid (ca 50,000 kwachas) for horn stubs, but with the development of Intensive Protection Zones (IPZS) and Conservancies in Zimbabwe (several far from the northern border), the incentive to hunt is less, especially when the distances to reach certain rhino areas are considerable, returns are relatively small and chances of being killed or apprehended greater. For example, the IPZs in Zimbabwe are approaching manpower levels of one scout per rhino, with incentives and increased coverage.
Table 1. Black and white rhino immobilised for dehorning, relocation and radio-collaring in Zimbabwe, 1991-1993.
Mortality A = unknown causes, could be natural, trauma, or undetermined
Mortality B = due to illegal hunting after dehorning
Mortality C = related to immobilization
Immobilized Dehorned Mortalities A Mortalities B Mortalities C
White rhino 156 136 2 70 6
Black rhino 322 224 7 19 1
Geldenhuys 1994 - dehorning in Namibia
A marked increase of poaching in 1989 prompted the decision of dehorning some black rhino populations in Namibia. The most vulnerable populations were identified and dehorned. Amongst the first black rhino to be dehorned were the unique desert-adapted rhino of Namibia's Kunene Province. Subsequently new sanctuaries have been established and stocked with dehorned rhino. Two calves were born in one of these populations three years after it was established.
FACTORS THAT LED TO THE DECISION TO DEHORN
1 . The nature of the vast semi-desert area of the northern Kunene Province which is inhabited by pastoralists and nomadic farmers without any formal conservation status. These farmers were armed with rifles and automatic firearms (with very little control) during the war. This led to poaching of the black rhinos, amongst other game.
2 . Lack of personnel, funds and equipment, by the conservation body, to effectively protect this vast area. Even with the input of Non-Government Organisations like Save The Rhino Trust Fund.
3. The open terrain would make the rhino visible without a horn and deter the poacher from shooting the animal.
4. The intensity of the monitoring program would make it possible to dehorn all individuals in the population, eliminating the chance of horned and dehorned rhinos interacting.
5. The virtual absence of large predators in the region make potential calf predation an unlikely event.
6. Due to the vegetation strata, very little use is made of the horn for browsing purposes.
7. The strong feeling that re-introducing rhino in that harsh environment will be extremely difficult. In situ protection was therefore of cardinal importance.
8. The experience of the capture team made it a minimal risk operation which could be done relatively cheaply.
9. Using the media to inform the public of newly-established sanctuaries with dehorned rhino.
METHODS
After darting from a helicopter or on foot, the animal is placed in sternal recumbency. The head is placed on a pillow, the eyes are shielded from dust and hot exhaust gases emitted by the power saw, the dart wound is treated and the vital functions monitored.
A rhino horn has a concave base where it fits over the nasal bones. This is especially marked with the anterior horn. This necessitates removing the anterior horn 6,5 cm from its base and the posterior horn 5 cm from its base. Using the bow and crosscut saw, excess horn was removed by hoof clippers. It is trimmed to a convex shape with the power-saw, leaving as little horn as possible without touching the quick.
Ear nicks are put in to give a new identity to the animal.
The left hindfoot's nails are nicked. The outer nail as well as the large front nail receive grooves, cut in with a power-saw or file. This acts as an indication to trackers that the animal being followed has already been dehorned, saving a lot of time.
Cows and small calves are both immobilized to prevent separation. Special emphasis is placed on getting the animals to wake up simultaneously, thus preventing their splitting up.
RESULTS
The mean time taken to dehorn a rhino, to assess its age and to put nicks in the ears and nails is 30 minutes. It is important to get the animal down in the shortest possible time. The use of Dehorninglazine rather than azaperone and hyaluronidase with etorphine gives rapid immobilization with induction times of 2 minutes 20 seconds to 4 minutes'.
No mortalities have occurred during all the dehorning exercises. Normal rhino behaviour, mating and breeding have prevailed since the first dehorning in 1989.
Horn regrowth varies between young and old animals, but allow three to four years between dehornings.
DISCUSSION
In Namibia dehorning has proved to be a management option. No dehorned rhino have been poached in Namibia. The Namibian exercise of giving custodianship of black rhinos to farmers helps to take the potential poaching burden off these farmers' shoulders. The cost under Namibian conditions comes to US$ 1500 per animal.
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