A survey of elephants (Loxodonta africana) in the Kahuzi-Biega National Park lowland sector and...

Afr. J. Ecol. 1997, Volume 35, pages 213–223

A survey of elephants (Loxodonta africana) in theKahuzi-Biega National Park lowland sector and adjacentforest in eastern Zaire†

JEFFERSON S. HALL1*, BILA-ISIA INOGWABINI1,ELIZABETH A. WILLIAMSON2, ILAMBU OMARI3,CLAUDE SIKUBWABO3 and LEE J. T. WHITE1

1Wildlife Conservation Society, International Conservation, 185th Street and Southern Blvd.,Bronx, NY 10460 U.S.A.; 2University of Stirling, Department of Psychology, StirlingFK9 4LA, U.K.; 3Institut Zairois pour la Conservation de la Nature, Avenue des Cliniques,Kinshasa, Zaire.

SummaryThere has been considerable uncertainty about the abundance estimation ofLoxodonta africana within tropical lowland moist forests in Zaire. We surveyeda 15,570 km2 area within the forests of eastern Zaire using transect samplingmethods and estimated the elephant population to be 3720 (range 2300–5000)individuals. Dung pile densities were significantly different between adjacentsettlement, deep forest, and deep forest core strata, with the most remote areaharbouring the highest density. Evidence of elephant poaching was encounteredthroughout the survey area suggesting that elephant populations continue to beat severe risk.

Key words: conservation, elephant, forest, poaching, survey, Zaire

RésuméIl existe une serieuse incertitude quant aux estimations de l’abondance deLoxodonta africana dans les forets tropicales humides de basse altitude au Zaıre.Nous avons etudie une superficie de 15.570 km2 dans les forets de l’est du Zaıreen employant les methodes d’echantillonnage par transect et nous avons estimequ la population d’elephants comptait 3.720 individus (entre 2.300 et 5.000). Ladensite des excrements etait significativement differente entre les endroits voisinsd’installations humaines, la foret profonde et le centre de la foret, les endroits lesplus recules etait les plus densement peuples. On a constate dans toute la zonedes recherches des preuves de braconnage d’elephants, ce qui laisse entendre queles populations d’elephants continuent a etre serieusement en danger.

Introduction

In recent years there has been considerable concern about the status of elephants(Loxodonta africana (Blumenbach)) in central Africa. While the effects of

*Correspondence: Yale School of Forestry and Environmental Studies, Marsh Hall, 360 ProspectStreet, New Haven, CT 06511, U.S.A.

†Now Democratic Republic of the Congo.

? 1997 East African Wild Life Society.

poaching have been readily evident in savanna regions, much of what wasbelieved about elephants inhabiting the forest has been based on guesswork(Barnes, Blom, & Alers, 1995a). A concerted effort to assess the elephantpopulation within central African forests began in the late 1980s (Barnes et al.,1995a). Since that time estimates have been made for Gabon (Barnes et al.,1995b), parts of the Central African Republic (Carroll, 1988; Fay, 1991),northern Congo (Fay & Agnagna, 1991), and south-eastern and south centralCameroon (Stromayer & Ekobo, 1992; Williamson & Usongo, 1995). Inaddition, an estimate has been offered for Zaire based on preliminary surveys oftargeted remote areas (Alers et al. 1992).

Given its vast forests, there continues to be much uncertainty concerningelephant abundance estimates for Zaire (Michelmore et al., 1994; Barnes et al.,1995a). Recently, studies have been undertaken to improve elephant densityestimates for large parts of eastern Zaire (Hart & Sikubwabo, 1994; Hart & Hall,1996). This paper reports on the distribution and abundance of elephants withina 15,570 km2 forest block between the Lowa, Luka, Lugulu and Oku rivers ineastern Zaire (Fig. 1). In addition, we discuss evidence of elephant poaching andits implications.

Fig. 1. Map of the study area between the Lowa, Luka, Lugulu, and Oku rivers in eastern Zaire.Sampling zones KB 1 to KB 4 and K 1 to K 3 represent Kahuzi-Biega and Kasese sampling zones,respectively.

214 J. S. Hall et al.

? East African Wild Life Society, Afr. J. Ecol., 35, 213–223

Study SiteThis survey was undertaken within the lowland sector of Kahuzi-Biega NationalPark (700–1800 m altitude) and adjacent forest in the Kasese area (600–1400 maltitude) between the Lowa, Luka, Lugulu and Oku rivers (26)51* and 28)51*west longitude and 1)18* and 2)29* south latitude; Fig. 1). In this region,vegetation is predominantly mixed mature tropical lowland moist forest(Yumoto et al., 1994). The year is divided into four seasons: short dry season,December to March; the long rainy season, March to June; the long dry season,June to September; the short rainy season, September to December (Yamagiwaet al., 1994).

Access to the survey area is limited by the deteriorating road network.Beyond a poorly maintained stretch of private road owned by a mining companythat links Kibereketa to the north-west by way of Kasese, the road networkwithin the survey area has been abandoned. Today, extensive stretches of formerroads are occupied by well established secondary forest and have served as littlemore than footpaths for many years (Fig. 1).

Methods

This survey was undertaken between January to August 1994 and March toJune 1995. Our principal goal was to determine the present day distributionand abundance of Gorilla gorilla graueri Matschie. A secondary goal wasto determine the abundance and relative densities of other large mammals,including the African elephant.

We sampled seven zones in the area bounded by the Lowa, Luka, Lugulu andOku rivers; four zones were within the Kahuzi-Biega National Park and threezones were in the adjacent Kasese region (Fig. 1). This area was chosen becauseit was the area believed to harbour the largest extant Grauer’s gorilla population.Elephant densities in Gabon have been found to increase with distance fromhuman settlements and roads (Barnes et al., 1991). Our sampling zones werestratified to test this relationship for elephants and other large mammals whilealso taking into account differences in vegetation revealed by the use of satelliteimages. Thus, we stratified survey areas in two ways: (i) by proximity and relativeease of access to a region very densely populated by humans (Kahuzi-BiegaNational Park (KB 1 to KB 4) vs. Kasese survey areas (K1 to K3)) and (ii) bysampling zones within survey areas based on proximity to human settlements,existing or abandoned roads serving as important footpaths, and coarse scaledifferences in vegetation (Table 1).

Transects have been shown to be an effective way of sampling remote,difficult to access, heterogeneous forested areas (Barnes, 1993). We used linetransects to sample elephant dung, ape nest sites and other large mammal signs.We placed between five and six transects at random intervals along a baselineand perpendicular to the predominant drainage feature in each sampling zone.One observer searched for large mammal signs on the ground while othersrecorded vegetation type and searched for ape nest sites (Hall et al., in press).The distance along the transect and the perpendicular distance were recorded foreach elephant dung pile observed along transects, following Barnes & Jensen(1987).

Elephant survey in eastern Zaire 215


We used distance sampling methods described in Buckland et al. (1993) andthe computer program developed by Laake et al. (1994) to calculate thedung pile detection function and density. Dung pile densities and standard errorswere subsequently compared between sampling zones using z-tests to determinewhich zones could be reasonably pooled to form a single estimate of densitywithin a stratum (Buckland et al., 1993).

Elephant densities were calculated assuming a steady state system followingthe formula described by McClanahan (1986) and Barnes & Jensen (1987):

E=Y#r

,D

where E=elephant density, Y=dung pile density, r=daily rate of dung pile decay,and D=number of droppings produced per elephant per day.

Dung pile decay is a complex process that follows neither a normal nor anexponential distribution (Barnes & Barnes, 1992; White, 1995) but in some casesmay follow a Poisson distribution (White, 1995). To determine 95% confidenceintervals we bootstrapped parameter values for each estimate 1000 times,sampling with replacement. Elephant dung densities were weighted by stratumarea prior to bootstrapping to calculate confidence intervals for the entire surveyarea and Kahuzi-Biega National Park. We then combined parameter estimates atrandom to obtain 1000 estimates of elephant density. Our 95% confidenceintervals are the 26th lowest and 975th highest values (Barnes, 1993).

Neither dung pile decay nor defaecation rate were measured during thisstudy. As other authors, we used rates determined elsewhere (Fay, 1991; Alerset al., 1992; Hart & Sikubwabo, 1994; Barnes et al., 1995b). Precipitation at thetime of dung deposition has been shown to be an important factor affecting thedung decay process (Barnes & Barnes, 1992). Dung pile decay time was drawnfrom a recent study conducted by Hart & Bengana (1996) in the Ituri Forest

Table 1.Map distance and kilometres of transect within distance categories of roads, major footpaths, andhuman settlements

Samplingzones

Distancerange (km)a

Total kilometres of transects

Broad vegetation classification0–11·5 11·5–20 >20

KB 1 0–20 46 30 0 Mixed with abundant secondary forestKB 2 11–30 19 39 10 Mixed forestKB 3 20–35 0 0 75 Mixed forestKB 4 0–20 88 12 0 Mixed forestK 1 0–10 53 0 0 Mixed with abundant secondary forestK 2 18–27 0 2 52 Predominantly Gilbertiodendron and

mixed forestK 3b 5–20 18 36 0 Mixed forest with abundant ‘Kisululu’c forest

aFlat map distance from roads or major footpaths.bK 3 sampling zone is located south-east of a dirt track created by a mining company and presentlyserving as a footpath. Mining camps are established but no permanent settlements with agriculturalproduction are present.c‘Kisululu’ is predominant, unknown tree defining habitat class (Hall et al., in press).



and chosen because proximity to our study site may best reflect the actualclimatic conditions found there (annual precipitation of 1711 mm (Hart &Bengana, 1996) is believed closer than Lopé, Gabon where mean annualprecipitation was 1506 mm over an eight year period (White, 1995)).

Mean dung pile decay time was 43·1 days for three data sets that include twowet season and one dry season sample (N=84; Hart & Bengana, 1996). The twowet season decay times were markedly different (44 days, N=26; 32·8 days,N=30). Hart & Bengana (pers. comm.) believe that the proximity of dung pilesin the latter wet season sample suggest that dung came from the same group ofelephants who were subject to the same microsite conditions, and may thereforenot accurately reflect all the factors contributing to the dung decay processduring the wet season. We resolved the problem of bias due to an apparentlyunique data set by combining all three data sets. We used defaecation ratesdetermined by Tchamba (1992) where mean defaecation rate was 19·8 droppingsper day, as suggested by Barnes et al. (1995b).

ResultsElephant dung and density estimateWe recorded 533 elephant dung piles (categories A – D as per Barnes & Jensen,1987) within 400 cm perpendicular distance along 480 km of transects (Table 2).Almost 52% of the dung piles were recorded along 75 km of transects within the574 km2 KB 3 sampling zone. A further 22% of the dung piles were recordedalong the 68 km of transects within the KB 2 sampling zone. By contrast, nodung piles were recorded within the KB 1 sampling zone and only 2% of thedung piles were recorded along 100 km of transects within the KB 4 samplingzone. We recorded 2% of the dung piles along 53 km of transects within the K 1sampling zone and 13% and 9% of the dung piles within 400 cm perpendiculardistance of the transect for sampling zones K 2 and K 3, respectively, both ofwhich had a total length of 54 km. The percentage of elephant dung encounteredon transect segments in relation to actual or abandoned roads and independentof sampling zones is presented in Table 3.

To determine the elephant dung pile detection function we combined all dataand discarded observations beyond 400 cm perpendicular distance from thetransect such that ~5% of our data points were disregarded (Buckland et al.,

Samplingzone Area (km2) N

Transectlength(km)

Dung piledensity

Standarderror

KB 1 290 0 76 0·0 —KB 2 243 115 68 608·1 119·1KB 3 574 277 75 1337·4 273·9KB 4 390 12 100 43·2 18·7K 1 180 11 53 74·8 51·4K 2 144 72 54 479·6 127·0K 3 180 46 54 306·4 101·2

Table 2. Dung pile densities andstandard errors by samplingzone



1993). We compared four default models provided by (Uniform keywith cosine adjustment terms, Uniform key with polynomial adjustment terms,Half normal key with hermite polynomial adjustment terms, and the Hazard ratekey with cosine adjustment terms) and concluded that the Uniform key functionwith six cosine adjustment terms provided the best fit to our data set (Fig. 3).

We compared dung pile densities and standard errors for each sampling zoneusing a z test and found the KB 3 sampling zone, our ‘deep forest core’ stratum,to have significantly higher densities than all other sampling zones (P=0·05). Inaddition, we found sampling zones KB 2, K 2, and K 3 to have significantlydifferent densities (P=0·05) from those of sampling zones KB 4, and K 1 but notfrom each other. Thus, we combined these zones to form our ‘deep forest’stratum. Sampling zones KB 1, KB 4, and K 1 are all located adjacent to actualor abandoned roads and areas of high human settlement and were combined toform our ‘adjacent settlement’ stratum (Fig. 2). Point estimates for the density ofelephants by stratum varied between 0·04 and 1·55 elephants per km2

(Table 4).

Elephant abundanceWe estimated a total of 3720 elephants (between 2300 and 5000, 95% confidenceintervals) in our 15,570 km2 survey area. We estimate 430 elephants (between 110and 850, 95% confidence intervals) in our adjacent settlement stratum, 2400elephants (between 1500 and 3200, 95% confidence intervals) in our deep foreststratum and 890 elephants (between 480 and 1300, 95% confidence intervals) inour deep forest core stratum. These estimates do not consider the effects ofprojecting data collected in a geographically heterogeneous area to flat mapareas and therefore underestimate the actual number of elephants within ourstudy area.

Human sign and elephant poachingHuman sign encounter data are presented and discussed elsewhere (Hart & Hall,1996; Hall et al., in press); however, a brief overview is presented here in relationto elephant poaching. We found signs of human use in all sampling zones andincidence of human sign on transects was significantly higher in our adjacentsettlement stratum from those of deep forest and deep forest core sampling zones(Hall et al., in press). In sampling zones adjacent to human settlement (Fig. 1),many of the signs resulted from activities associated with hunting, fishing and thegathering of forest products. Evidence of small-scale mining and associatedcommercial hunting was widespread and camps associated with these activitiesreportedly provide a base of operations for elephant poachers. Evidence of

Distance range(km)

Dungpiles

Effort intransect-km.

Dung pileskm"1

Percent dungpiles km"1

0–11·5 23 224 0·10 2%11·5–20 77 129 0·60 15%>20 433 127 3·41 83%

Table 3. Dung piles andpercentage dung piles perkilometre of transect in distancecategories



elephant poaching was found in all four deep forest and deep forest coresampling zones; carcasses from recently poached elephants and poachers campswith large drying racks for meat were encountered within or adjacent to three outof four of these remote sampling zones.

DiscussionComparison of results to other studiesThese results differ slightly from preliminary results presented elsewhere (Hart &Hall, 1996). The most important difference results from changes in the poolingof sampling zones. The preliminary discussion offered in Hart & Hall(1996) considered densities within and outside the national park boundariesindependently of one another.

Other differences between the preliminary presentation of the data andthe one contained herein result from different parameter estimates used fordefaecation rate and dung pile decay time. The defaecation rate used here(Tchamba, 1992) is slightly higher and believed to be a more accurate estimate ofactual forest elephant defaecation rates (Barnes et al., 1995b) than that used inHart & Hall (1996). Furthermore, because it is a set composed of multiplesamples, we were able to bootstrap data to obtain more accurate confidence

Fig. 2. Map of deep forest core, deep forest, and adjacent settlement strata. Adjacent settlement stratumis the non shaded portion of the study area.



intervals (Barnes, 1993). Finally, the mean decay rate is slightly faster than the45 day decay previously employed. By using the Hart & Bengana (1996) data set,once again we were able to bootstrap data sets and obtain better confidenceintervals. The differences described here would result in minor effects on the finalestimate as the increased defaecation rate and decay time are similar inmagnitude and have opposite effects.

Our results differ markedly from those reported by Merz (1989) and usedby Alers et al. (1992) to estimate the total number of elephants within Zaire.Merz believed ~9000 elephants inhabited the Kahuzi-Biega National Parklowland extension sector whereas we estimate 1900 elephants (between 1100 and2500, 95% confidence intervals). This difference should not be interpreted as

Fig. 3. Number of dung piles observed by perpendicular distance category from transects. Dark shadedcolumns furthest to left represent all data combined; grey columns second from left represent KB 3 or deepforest core stratum only; charcoal shaded columns third from left represents deep forest stratum data;light shaded columns furthest to right represents adjacent settlement stratum data.

Table 4. Dung pile densities, standard errors, elephant density and 95% confidence intervals for eachstratum

StratumArea(km2) N

Distancerange(km)

Dung piledensity

Standarderror

Elephantdensity

ind. km"2Confidenceintervala

Adjacent settlement 10,634 23 0–20 36·2 17·3 0·04 0·01–0·08Deep forest 4,362 233 5–30 476·1 74·3 0·55 0·34–0·75Deep forest core 574 277 20–35 1337·4 273·9 1·55 0·83–2·29

aDerived from bootstrap estimates.



representing a precipitous decline in the elephant population in just a few shortyears, but rather due to a difference in methodologies.

Merz (1989) was charged with making an assessment in one month of a5400 km2 area where access is extremely difficult. He walked 112 km of forestreconnaissance in the Kahuzi-Biega lowland forest extension, much of which wasthrough areas where we found very high densities of elephants. He then usedresponses to questionnaires administered by collaborators to attempt to deter-mine how to best extrapolate his forest reconnaissance data across the entirearea. Based on these questionnaires, he indicated the presence of elephantswithin our KB 4 sampling zone and extending throughout the south-westportion of the extension. In contrast, we found very low densities in KB 4 andbelieve that the very high mining activity in the south-western portion of thelowland extension results in low elephant densities. Based on proximity to roadsand the mining centre at Lulingo, we included much of this area in our adjacentsettlement stratum (Fig. 2). Thus, we feel that Merz’s high estimate in relation toour own results from his inadvertent extrapolation of densities to areas wherefew elephants are found rather than a marked decline in elephant densities.

One problem that arises when attempting to compare elephant densities isthat data have been collected in many different ways and authors have useddifferent parameter estimates to calculate the number of elephants. Barnes et al.(1995b) conducted a sensitivity analysis on the elephant dung deposition par-ameter and determined that the standard errors from observed data have arelatively small effect on the standard error of the final estimate. In contrast, dungdecay rates can vary widely between seasons and sites (White, 1995). The meanestimate calculated from the Hart and Bengana dry and wet season data set (43·1days) is very similar to those observed in Gabon by Barnes & Barnes (1992) andWhite (1995). Finally, the dung pile density estimate has been calculated in manydifferent ways (Fay, 1991; Hart & Sikubwabo, 1994; Barnes et al., 1995b). Ourstudy used a stratified sampling design where transects were randomly placedwithin sampling zones. We further used (Laake et al., 1994) to obtain arigorous estimate of the point estimate and confidence intervals.

A comparison of dung pile densities between sampling zones showed a similarrelationship to one in Gabon where elephants were found in very low densitieswithin forest adjacent to roads and human settlements (Barnes et al., 1991).These results support the use of this relationship in the model of elephantabundance across central African forests constructed by Michelmore et al.(1994). They found 64% of their dung piles in the Congo to be between 11·5 and33·5 km from roads. No point within our sampling zones was beyond 35 km mapdistance from abandoned roads that continue to serve as important footpaths.When adjusted for sampling effort, 98% of our dung piles were found beyond11·5 km from the nearest road or important footpath. Further, when scaled tosampling effort, 15% and 83% of our dung piles were found between 11·5 and20 km and beyond 20 km map distance from roads and important footpaths,respectively. That dung pile densities in two sampling zones where transects werealmost entirely beyond 20 km of roads, KB 3 and K 2, were significantly differentillustrates the limitations of extrapolating densities beyond study areas based onthis criterion alone. Nevertheless, our data support the use of these three broaddistance categories in sampling design for future surveys of forest elephants.



Poaching activities and conservation implicationsThe dramatic impact of the ivory trade on elephants inhabiting the forest hasbeen documented and discussed elsewhere (Michelmore et al., 1994; Barnes et al.,1995a; Hart & Hall, 1996). We documented extensive human use of even remoteforest areas (Hall et al., in press) and encountered abundant evidence of elephantpoaching. Elephants are only abundant within remote sectors of our survey areasand are presently absent from extensive areas of suitable habitat within theKahuzi-Biega National Park lowland sector. This evidence suggests that there islittle political will to combat elephant poaching within the forests of easternZaire and that elephants must be considered at extreme risk. Finally, while thevalue of ivory makes the case of elephants unique at present, their fate may wellforeshadow that of other large mammals. As the demand for bush meat increasesto meet the needs of eastern Zaire’s ever increasing human population, we mightexpect to see a sharp decline in large mammal densities adjacent to humansettlements, roads, and important footpaths. Sustained conservation efforts areimperative to counteract such trends.

AcknowledgementsThis survey was conducted as a collaboration between the Wildlife ConservationSociety (WCS) and the Institut Zairois pour la Conservation de la Nature(IZCN). We would like to acknowledge Mankoto ma Mbaelele, the Director ofthe IZCN during the period when this research was accomplished, for activelyencouraging and facilitating the survey. Financial support for this work camefrom the Wildlife Conservation Society with additional funds provided byBergorilla und Regenwald Direkthilfe. The Deutsche Gesellschaft fur TechnischeZusammenarbeit (GTZ) provided logistical assistance. We would like to thankall our colleagues for their assistance during the various phases of data collectionand analysis. We would particularly like to acknowledge the collaborationof J.D. Bakinahe, S. Bakinahe, D. Bonny, C. Fimbel, J. Hart, A. & W. Heisel,C. Iyumi, K. Kaleme, U. Karlawski, F. Koontz, H. Makindu, O. Mankoto,M. Mashagiro, G. Mutazimiza, H.S. Morland, N. Mwanza, K. Saltonstall,K. Sestritch, G. Servkeza, B. Stienhauer-Burkhart, P. Walsh, I. Weiche, J.Yamagiwa, and D. Yuma. M. Connor assisted in the preparation of maps. Dataanalysis was undertaken at the Science Resource Centre of WCS. K. Saltonstalland P. Walsh commented on earlier drafts of the manuscript. Finally, we owe anenormous debt of gratitude to our guides, porters, and field staff without whomthis work could not have been carried out.

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(Manuscript accepted 7 October 1996)



A survey of elephants (Loxodonta africana) in the Kahuzi-Biega National Park lowland sector and...

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