K.P. Erb

M. Lindeque

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Pachyderm No. 21, 1996 27RESEARCH ON THE EFFECTS OF TEMPORARY HORNREMOVAL ON BLACK RHINOS IN NAMIBIAMalan Lindeque and K. Peter ErbMinistry of Environment and Tourism, Private Bag 13306, Windhoek, Namibiain equal measure although no data were presented (Berger & Cunningham 1994a). The 1993 drought did andforegone the temptation of taking issue with thevarious allegations and speculations concerning theNamibian wildlife management authority and itspolicies, or indeed the respective roles of science inwildlife management and foreign scientists indeveloping countries.A chronology and summary of the circumstancessurrounding the three rhino deaths assumed to haveoccurred by Berger & Cunningham (1993, 1994a) arepresented (see Table), based on Berger & Cunningham(1993), Berger et al. (1993), Berger & Cunningham(1994a), and the unpublished data of MET KuneneRegion staff and B. Loutit of the locally-based “Savethe Rhino Trust” (SRT). The essence of the argumentthat temporary horn removal increases the risk ofspotted hyaena (Crocuta cmcuta) predation on calvesis given in Berger & Cunningham (1994a). Severalpoints of dispute are highlighted below.EXPERIMENTAL DESIGNBerger & Cunningham (1994a) contrasted calfsurvival in three areas (known as SR, DC and NYF)of hyperarid broken terrain in the Kunene region ofNamibia, previously known as Damaraland. Twoareas larger than 1,000km2 (SR and DC) eachcontained fewer than 20 rhinos which had all beendehorned once since 1989 (See Table). Largepredators allegedly occurred only in area SR and inthe third region where no rhinos were dehorned(NVF). Apart from our concern over extremely smallsample sizes as well as a different conclusion reachedby Martin (in press) using the same statisticalprocedure as Berger & Cunningham (1994a), flawsin the experimental design are obvious to thosefamiliar with the region and the environmentalconditions over the past few years. It is our beliefthat other important differences affecting rhinosurvival occurred between areas SR, DC and NVF,unrelated to predators or dehorning. The alleged rhinocalf deaths coincided with the worst drought in humanmemory in Namibia. Berger & Cunningham (1993)presented photographic evidence of emaciated adultrhinos in areas DC and SR in 1993, but later claimedthat the drought had affected their entire study areasINTRODUCTIONIn July 1993, Berger and Cunningham (1993)concluded in an unpublished progress report to theNamibian Ministry of Environment and Tourism(MET) that three black rhinoceros (Diceros bicornis)calves had died in the only part of their study area inthe Kunene region of Namibia where rhinos weredehorned and where large predators occurred. Theyclaimed that two black rhino calves born in 1992 couldnot be found in 1993, nor could they find a third calf,never seen, but which was assumed to have been bornto a dehorned female which had a swollen udder. Allthree alleged calf deaths were attributed to predationby spotted hyaenas and lions. This reportacknowledged, however, the possibility that only twocalves had died and that other factors such as droughtcould have accounted for their deaths. MET wasconcerned over several aspects of the report, butofficially regarded it as an interim progress report andnothing more.In February 1994, concern turned to disappointmentwhen it became evident that these preliminary datahad been submitted as solid fact in a paper to thepolicy forum section of Science (Berger &Cunningham, 1994a), and were cited as the basis forspeculation about the relative efficiency of alternativein situ rhino conservation strategies. The conclusionthat dehorning might not be an effective strategy wasconsidered by MET to be premature, not supportedby adequate data, and not in the best interests of rhinoconservation. The authors furthermore chose not toprovide clarification on some research methods andthe scope of their planned work in 1994 as requested,but terminated their study (even before MET hadconsidered not extending their research permit on thebasis of their article in  Science ). They havesubsequently gained support for their position fromtheir home base in the USA, for example, in Berger& Cunningham (1994b), Brussard (1994) andMacilwain (1994).In this paper, we examine the calf mortality data andinterpretations presented by Berger & Cunningham(1993, 1994a) and Berger et al. (1993). We have28 Pachyderm No. 21 1996Year Rhino security risks, management Average adult Births from Recorded blackintervention and environment female anterior horn dehorned mothers rhino deaths in theconditIons1 length (cm)2 in SR in SR SR part of theKunene region ofNamibia1989 High risk in SR, 20 dehorned in SR, 0 (1)33 translocated from SR1990 No poaching in SR or DC, 6.4 -1 killed in NVF area1991 High risk in DC, 8 dehorned in DC 12.8 -1992 No illegal hunting in SR or DC, onset 19.2 2 seen4 1 sub-adult (starvation)of drought, influx of livestock in SR 1 inferred5 1 calf inferred6(unknown causes)1993 No illegal hunting in SR or DC, 25.6 inferred4 3 calves inferred4serious drought; SR adults inemaciated condition31994 No illegal hunting, but security risk 32.0 17 1 adult (fromgrowing, drought conditions Staphylococcus sp.persist in parts of NVF, infection)SR and DC1. Summarised assessment from unpublished reports and data of MET and B. Loutit.2. Average female anterior horn lengths calculated from Berger et al. (1993).3. This calf was less than three months o/d when his mother was dehorned He has survived    (B. Loutit, SRT, andunpublished MET data).4. Two calves were recorded in 1992, and a third was never seen, only inferred from photos of a female with a swollenudder (Berger & Cunningham, 1993).5. Results of a 1992 photographic census of rhinos by SRT and MET6. Calf positively recorded but with no subsequent appearances (B. Loutit, SRT and unpublished MET data).7. B. Loutit, SRT, pers. comm.Table. A chronology of black rhino conservation problems and management intervention in areas SR, DC and NVF of theKunene region of Namibia.affect a large part of the Kunene region, butNormalized Difference Vegetation Indices derivedfrom NOAA satellites indicate substantially moreactively growing vegetation, and thus biomass, inparts of area NVF than in either DC or SR(unpublished MET data).Apart from being located in a vegetation zonecompletely different from the other two areas (Geiss,1971), area NVF is managed as a tourism concessionand de facto conservation area with negligiblepresence of livestock, and is partly fenced by a stock-proof veterinary cordon fence. Areas DC and SR areunfenced communal lands used by semi-nomadiclivestock farmers. Surface water is scarce throughoutthe region, but more so in DC and SR than in NVF.Some 500 small stock (goats and sheep) and cattlewere moved into the SR rhino concentration areaduring the 1993 drought, which severely depletedwater supplies and displaced black rhinos from theirusual watering points (Loutit & Montgomery, in press;B. Loutit, pers. comm.) A lesser influx of people andlivestock occurred over a shorter period in DC butnothing comparable occurred in NVF. Berger andCunningham must have been aware of this, and indeedhave cited the increased pastoral use of areas DC andSR during the drought as probable causes of rhinopopulation decline (Berger & Cunningham, 1993).The experimental design presented by Berger &Cunningham (1993, 1994a) thus represents an artificialPachyderm No. 21, 1996 29oversimplified experiment (with no control, see Martin,in press) not taking account of other environmentalfactors, and therefore cannot reveal anything about rhinocalf survival as a consequence of dehorning or any othermortality factor.PREDATOR AND PREY DENSITIESIN THE KUNENE REGIONA contrast in the experimental design of Berger &Cunningham (1994a) is the presence and absence oflarge carnivores in three parts of a large study area innorthwestern Namibia, variously described as ca.7,000km2 (Berger & Cunningham, 1994a) or 10,000km2(Berger & Cunningham, in press) or 4,500km2 (Berger,in press). There are enormous logistical andmethodological problems in determining large mammaldensities in large areas of broken terrain, especially ifan aircraft is not used, as, for example in the study ofBerger and Cunningham. The two researchers have notexplained their methods of monitoring mammaldensities, but these could not have been more thansightings of animals and their tracks at waterholes andalong the few roads in the region. Such methods mayyield valid estimates of ungulate densities undercontrolled conditions, but we know of no situation inarid savanna or desert regions where such methods havebeen considered useful for estimating densities of largeAfrican carnivores. Experienced MET ranger andresearch staff consider it most unlikely that more than30 spotted hyaenas or more than 1O lions occur in theentire 40,000km2 of the “Damaraland” part of theKunene region, as also suggested by the low reportedincidence of predation on livestock in this region(unpublished data, MET). Berger (in press), concedesan estimate of 1O hyaenas in 4,500km2 in “centralKaokoveld”.The brown hyaena Hyaena brunnea (which almostnever preys on large mammals [Mills, 1990; Skinner& Smithers, 1990]), occurs throughout the Kuneneregion of Namibia, and partly overlaps in trackdimensions with spotted hyaenas Crocuta crocuta.Much of the region has coarse substrates not suitablefor accurate distinction between the tracks of relatedspecies. Intriguingly, Berger & Cunningham (1993,1994a) report no hyaena presence from area DC at all,while both species have regularly been recorded there(Skinner & Smithers, 1990; unpublished MET records;pers.obs.) Spotted hyaenas were found at the carcass ofthe sub-adult rhino which died in 1992 (Table 1) in theDC area which, according to Berger & Cunningham,had no large predators at all. In a later manuscript, Bergerand Cunningham (in press) mention that the number ofspotted hyaenas had not been determined in their studyarea, and yet they state elsewhere with conviction thatsome parts of their huge study area had no hyaenas whileother parts did.We conclude that their survey methods were inadequate,given the importance attached to apparent differencesin predator density as a factor in rhino calf survival.There is, in fact, no evidence for predation on rhinocalves in area DC, where both species of hyaena occursympatrically with rhinos which were dehorned in 1991.PREDATION ON RHINOSBy accepting that black rhino calves are vulnerable tospotted hyaena and lion predation, one cannot simplyconclude that any missing black rhino calves in theKunene region are therefore killed by predators. Nocarcasses of any calf born in 1992 or later have beenlocated. There is no evidence to suggest that eitherpredation was the cause of death of three rhino calveswhen their carcasses were never recovered, or that calfpredation was related to a horn reduction exercise threeyears earlier!Interesting questions may nevertheless be asked aboutpredation on rhinos, such as “How much horn does arhino mother need to deal with a predator?”, or “Is therean optimal size or shape for a rhino mother’s horn?”.As evident from the table, Berger (1993a) and Bergeret al. (1993), the anterior horns of the three dehornedmothers had already regrown to between 19 and 26cmby the time their calves had allegedly disappeared. Thislength of horn overlaps with the natural distribution ofadult horn lengths (Berger et al., 1993). Rhino hornshapes and lengths show extreme variation under naturalconditions and the horns are the main features used inindividual recognition of rhinos by researchers insouthern Africa This suggests that horn dimensions perse are not that important for the protection of calves. Itseems likely that if maternal horn length and shape areimportant for the protection of the calf, these parameterswould have evolved towards an optimum shape andlength rather than varying to the degree seen in allpopulations.TEMPORARY DISASSOCIATIONSBETWEEN RHINO MOTHERS ANDCALVESThe fact that black rhino cows hide their small calveshas been reported inter alia by Joubert & Eloff (1971),Hall-Martin & Penzhorn (1977) and Owen-Smith(1988), and not for the first time as claimed by Berger30 Pachyderm No. 21 1996(1993b). Berger & Cunningham (1994a) alleged thatall three calves disappeared within one year after birth,during the interval that calves are most often hidden(Berger, 1 993b). Berger & Cunningham (in press)also recorded spatial displacement by females ofseveral kilometres in one day in response to humanpresence. No more extreme than their predation theoryis the speculation that Berger and Cunningham’sactivities and presence might have also affected theperiod of separation between cow and calf, especiallyin situations compounded by drought, poor bodycondition and displacement from watering points.No data have been published comparing the vulnerabilityof hidden calves versus those accompanied by theirmothers, or the proportion of time spent in hiding atvarious age intervals. If calves are preyed on whilst inhiding, maternal horn length is of no consequence. Thispossibility should have been discussed in any paperdealing with predation on rhino calves.CONCLUSIONSConsidering that rhino cows hide their small calves;that horn shape and length show tremendous naturalvariation, indicating the lack of any strong evolutionaryselection towards an optimum defensive utility; andconsidering the adverse habitat conditions experiencedby the SR rhinos at the time when they seem to havelost their calves; we have to conclude that there is nosupport for any claim that a prior dehorning exercisehad affected calf survival. No evidence exists that anycalf died from predation or any other cause such as beingabandoned during extreme drought conditions. Untilunambiguous proof exists that the same females whichwere said to have lost calves, have indeed lost theircalves, any conclusion about the effects of dehorningon calf survival is irresponsible speculation.REFERENCESBerger, J. (1993a) Rhino conservation tactics. Nature361, 121.Berger, J. (1993b) Disassociations between blackrhinoceros mothers and young calves: ecologicallyvariable or, as yet, undetected behaviour? Afr. J. Ecol.31, 261-264.Berger, J. (In press) Science, conservation, and blackrhinos. J. Mammal.Berger, J. & Cunningham, C. (1993) Black rhinoconservation: problems and progress.  Unpublishedprogress report submitted to the Ministry of Wildlife,Conservation & Tourism.Berger, J. & Cunningham, C. (1994a) Activeintervention and conservation: Africa’s pachydermproblem. Science 263, 1241 - 1242.Berger, J. & Cunningham, C. (1994b) Black rhinoconservation. Science 264, 767.Berger, J. Cunningham, C. (In press) Predation,sensitivity, and sex: why female black rhinocerosesoutlive males. Behav. Ecol.Berger, J., Cunningham, C., Gawuseb, A.A. & Lindeque,M. (1993) “Costs” and short-term survivorship ofhornless black rhinos. Cons. Biol. 9, 920-924.Brussard, P.F. (1994) Science and conservationagencies: still an uneasy partnership. Society forConservation Biology Newsletter 1. Issue 2.Geiss, W. (1971) A preliminary vegetation map ofSouth West Africa. Dinteria 4, 1 - 114.Hall-Martin, A.J. & Penzhorn, B.L. (1977) Behaviourand recruitment of translocated black rhinoceros.Koedoe 20, 147-162.Joubert, E. & Eloff (1971) Notes of the ecology andbehaviour of the black rhinoceros in South WestAfrica. Madoqua 1, 31-36.Loutit, B. & Montgomery, S. (In press) Rhinoconservation. Science.Macilwain, C. (1994) Biologists out of Africa overrhino dispute. Nature 368, 677.Martin, R.B. (In press) Evaluation of the effects ofremoval of horns from rhinos. Cons. Biol.Mills, M.G.L. (1990) Kalahari Hyaenas. UnwinHyman, London.Owen-Smith, R.N. (1988)  Megaherbivores.Cambridge University Press, Cambridge.Skinner, J.D., & Smithers, R.H.N. (1990) Themammals of the Southern African subregion.University of Pretoria, South Africa.

Research on the effects of temporary horn removal on black rhinos in Namibia

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Research on the effects of temporary horn removal on black rhinos in Namibia

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