Seasonal distributions and social dynamics of ...

Seasonal distributions and social dynamics of elephants in t he Hoanib River catchment, northwestern Namibia Keit h Leggett*, Julian Fennessy & Stephanie Schn eider Hoanib River Catchment Study, Desert Research Foundation of Namibia, P.O. Box 20232, Windhoek, Namibia Received 1 October 2001 . Accepted 7 November 2002

Studies on the elephants of the Hoanib River catchment are limited. The most significant research undertaken during a period of drought and civil war inducing a high stress situation for the elephants. The only other reported study was undertaken at the end of the Namibian civil war and focused on elephant range and movement and did not carry out an in-depth analysis of the elephants ecology. The current study examined two distinct populations of elephants separated by an area with a high human population. The average group size of elephant herds in both the eastern and western sections of the catchment has declined steadily from the early 1980s until the present day. Average group size also appeared to be seasonally dependent, with larger group sizes observed during the cold-dry and wet season in the eastern catchment and during the wet and hot-dry season in the western catchment. The social interactions between elephants were investigated in the western section of the catchment only. Associations between different family units were only loose affiliations Jacking the strong social bonds reported from other areas of Africa. Adult male group associations were shown to be transient and irregular, with small group size. Key words: desert-dwelling elephants, social organization, group size, movement.

INTRODUCTION

Although the desert-dwelling elephants, Loxodonta africana (Blumenbach 1797) of northwestern Namibia are tourist attractions, there have been few scientific studies of this population (Viljoen 1987, 1988, 1989a,b; Viljoen & Bothma 1990; Lindeque & Lindeque 1991). Viljoen' s (1988) study was undertaken during a period of stress for the elephants caused by severe drought and heavy poaching. The study by Lindeque & Lindeque (1991) focused on range and movement and did not examine elephant ecology. However, the population of desert-dwelling elephants has been regularly monitored by the Namibian Ministry of Environment and Tourism (MET) (Owen-Smith 1970; Joubert 1972; De Villiers 1975; Visagie 1977; Le Roux 1978; Carter 1990; Loutit 1993; Loutit 1995; Specialist Support Services 1999), yet little recent information has been available on herd sizes, group interactions and seasonal movements. Before 1900 the elephant population in northwestern Namibia was estimated to be between 2500 and 3500 (Viljoen 1987). This population was hunted extensively in the latter part of the 19th century without evidence of a decrease in numbers *Author for correspondence.E-mail:[email protected]

(Viljoen 1987). By the 1960s, however, the number of elephants in the northwest was thought to have declined to between 600 and 800 due to expanding human settlements, intensive hunting and poaching (Owen-Smith 1970). By 1983, this number was further reduced by intensive poaching, war and drought, to approximately 360 individuals (Viljoen 1987). It is thought that elephant numbers have recovered since this time, and are now approximately 760 (Specialist Support Services 1999). By the 1980s the northwestern population of 360 elephants appeared to be split into three distinct populations (Fig. 1) with no apparent contact between the eastern and western populations (Viljoen 1987). Possible genetic exchange could have occurred between these populations via the transitional population that moved between the eastern and western elephants. However, Viljoen (1987) observed that the latter population only made infrequent contact with the other two population groups. A low calving percentage was recorded for all populations, which was attributed to poaching and human disturbance. From 1980 to 1983, Viljoen (1987) reported that poachers killed 123 elephant. By contrast, Lindeque & Lindeque (1991)

African Zoology 38(2): 305- 316 (October 2003)

·~

306

African Zoology Vol. 38, No. 2, October 2003

A ·WESTERN ANGOLA

8

POPULATION

·TRANSITIONAL POPULATION

...

10'

n'

l1

10

IS

l l)(h •

11'

Fig. 1. Elephant populations of northwestern Namibia (after Viljoen, 1988).

suggested that the distribution and status of elephants in northwestern Namibia reflected a skeletal elephant social organization, with no definite interaction between the eastern and western population groups. Viljoen (1987) reported that the social structure of the elephants in the Hoanib River exhibited a similar structure to that reported by Moss & Poole (1983) and Poole (1996). According to Poole (1996) a 'family unit' is defined as the basic unit and consists of one or several females and their offspring. Related families may form defensive units and kin-based allegiances, which in turn may have a positive affect on calf survival rate. 'Bond groups' or 'kin groups' are made up of several closely related family groups of up to five families. Bond groups form when family groups become too large and split along family lines. When bond groups meet, elaborate greeting behaviour is often

exhibited. Families and bond groups that have the same seasonal ranges are classed as 'Clans'. Clans are used to define a level of association around habitat use and it is unclear whether it is a functioning elephant social unit. Since the early 1980s, the northwestern Kunene Region has been the focus of conservation efforts. Community consultations conducted by the MET and non-government organizations (NGOs) have resulted in the mobilization of community support for conservation. This effort combined with effective law enforcement (MET with support from NGOs) has resulted in an increase in elephant numbers. They are now back to their 1960 levels of between 600 and 800 (Owen-Smith 1996). In light of the increasing economic and social importance of these elephants to emerging and established conservancies in the Hoanib River

Leggett et al.: Distribution and social dynamics of elephants in northwestern Namibia

307

Legend - - Hoanib Raver and Tribut.aries

c:::J

Protected Areas

~ Fenced Fatmland

Kh' t . .__. r···--+-·,. _ Etendeka"·,, 50

25

Kilon1eten:

! •

I!

'~~.

Western Catchment Eastern Catchment

N

t

Fig. 2. Location of the Hoan ib River catchment, Namibia.

catchment, the present study focused on establishing the number of elephant and their spatial and seasonal distribution. The study determined the group sizes of elephants, examining changes over time, and the influences that human activity has had on the stability of the elephant population. STUDY AREA

The Hoanib River catchment is one of twelve major ephemeral river catchments that occur in the semi-arid areas of northwestern Namibia (Fig. 2). All twelve rivers flow into the Atlantic Ocean or end in the Namib Sand Sea. Many originate in commercial farmlands, flow through communal farming areas and, near their mouths, traverse a protected conservation area . The Hoanib River catchment occupies an area of 17 200 km2, 3% of which lies in private farmlands, 91 % in communal farmlands and 6% is protected as Etosha National Park and Skeleton Coast Park Gacobson et al. 1995). Topographically, northwestern Namibia can be divided into three major regions (a) the interior highlands or escarpment zone, which reaches a maximum altitude of just over 2000 m; (b) the pro-Namib coastal plains; and (c) the plains of the Northern Namib Desert

(Hilton-Taylor 1994; Becker & Jurgens 2000). Rainfall in this area is highly variable and is dependent on the development of the Southern Intertropical Convergence (SITC) (Hutchinson, 1995). The main rainfall occurs from February to April, and the average rainfall in the Hoanib River catchment varies from 200 m), making them difficult to approach and observe. In addition, vegetation and water sources in the ECA are not confined to the riverbeds but are widely distributed. The WCA elephants were far more approachable and were 'confined' to areas in the riverbed where vegetation and water were available. These factors combined to make it easier to locate and study them. The only complete data sets collected during this study were those for the WCA The group associations observed between female and male elephants occurring in the ECA and WCA are presented in Tables 3 and 4, respectively.

It is recognized that male/female associations are

complicated by whether the females are in oestrus or not. However, as Viljoen (1988) pointed out, cows are remarkably tolerant of males and allowed them into the family units whether or not a cow was in oestrus. Historical male group associations in the WCA are presented in Table 4. An historical comparison between female groups was not possible, as the herd identifications used by Viljoen (1988) could not be recognized during this study. The results from Table 3 indicate that in the western section of the catchment, 22-38 % of groups observed were single adult females and their offspring. Very few permanent associations between adult females were observed in this area. Aggregations of females were observed to be more frequent at the end of the hot-dry season and into the wet season. These associations were generally very loose groups with adult females often being associated with several different females over a relatively short period. One adult female and her offspring were never observed to interact with any other female or female group. Adult male associations (Table 3) in the eastern and western Hoanib River showed completely


311

Table 2. Seasonal group size of Hoanib River catchment elephants, 1981/82 {after Viljoen 1988) and 1999/2000.

Number of sightings

Average group size

13 11 20 34 80 69

6.69 9.36 4.40 6.20 4.09 4.72

7.85 9.83 3.33 6.91 2.89 3.95

Eastern catchment area Wet, 1999 Wet, 2000 Cold-dry, 1999 Cold-dry, 2000 Hot-dry, 1999 Hot-dry, 2000

6 12 10 7 5 1

2.33 3.42 3.60 4.71 2.60 1.00

2.42 3.68 5.17 5.38 0.89 0

Western catchment area Wet, 1999 Wet, 2000 Cold-dry, 1999 Cold-dry, 2000 Hot-dry, 1999 Hot-dry, 2000

20 7 39 6 7 18

3.00 2.71 2.83 1.8 3.50 2.23

1.97 2.43 2.67 1.79 3.02 2.35

Season

Standard deviation

Viljoen (1988)

Wet, 1981 Wet, 1982 Cold-dry, 1981 Cold-dry, 1982 Hot-dry, 1981 Hot-dry, 1982 This study

different patterns. In the ECA adult males tended to form pairs or aggregate in groups greater than two, while in the WCA males were observed either as lone individuals or in small bachelor groups of no more than two individuals (t-test, P = 0.018). The percentage adult male associations in the ECA were similar to those reported by Viljoen (1987) (Table 4) for the WCA, where adult male groups constituted a significant percentage of observed associations. Seasonal distribution data for elephants in the

eastern and western catchment area are presented in Fig. 4. The data are a combination of aerial and ground survey results. The October/November 1999 survey was conducted prior to and just at the onset of the wet season. Fifty-nine elephants were observed in the Hoanib catchment (39 in the eastern catchment and 20 in the western catchment), with an additional 11 elephants observed in the Hoarusib River. The 1999/2000 wet season saw the best catchment-wide rainfalls recorded since 1976. During the aerial survey flown in April 2000,

Table 3. Adu lt Female associations (as a percentage) in the Hoanib River catchment, 1999/2000.

Sample size

% Single adult

female and offspring

% Breeding herds (> 1 female and

% Mixed group

associations 1

offspring)

Eastern catchment area Wet season Cold-dry season Hot-dry season

5 4 4

0 0 25

100 100 75

100 75 50

Western catchment area Wet season Cold-dry season Hot-dry season

32 35 22

22 38 35

78 62 65

58 37 43

' Mixed groups refers to whether or not adult males were observed with either single adult females or associated with family units

312


Table 4. Historical (1981-83) and current (1999/2000) adult male associations in the western Hoanib River catchment.

Season

Sample size

% of single adult

%of adult males

% of adult males

males

in pairs

in groups >2

% of adult males in groups of mixed sex

Vijoen's data (1988) Wet, 1980-83 Cold-dry, 1980-83 Hot-dry, 1980-83

48 96 141

16.7 16.7 32.6

16.7 29.2 32.6

0.0 29.2 21.3

66.7 25.0 22.0

Eastern catchment area Wet, 1999/2000 Cold-dry, 1999/2000 Hot-dry, 1999/2000

11 11 5

54 28 20

0 9 40

18 9 20

28 54 20

Western catchment area Wet, 1999/2000 Cold-dry, 1999/2000 Hot-dry, 1999/2000

15 30 17

60 79 65

0 10 6

0 0 0

40 11 29

only 31 elephants were observed. Twenty-four elephants were recorded in the eastern catchment, six in the western catchment and only one elephant was observed in the Hoarusib River. Although the deficiencies of aerial surveying are

Wet Season D1Stributton

Elephant Density

. 10

well-recorded (Pennycuick et al. 1972; NortonGriffiths 1978; Jachmann 1991), the difference in numbers recorded during these surveys was substantial. The above-average rains are thought to have caused a movement of elephants out of the Elephant Density

Cold-dry Season D1stribut1on

(numbtr of tnunals observed)

(number of arum.Ills observe

••.••o

•• •

'

1

N

t

Hot-dry Season D1str1btwon

Elephant Density (number of arumals observed)

•••• . o'

Possible Movement ~ Wet -~

Season Movement

Dry Season Movement

Fig. 4. Seasonal distribution and possible movement of elephants in the Hoanib River catchment, Namibia.


riverbed to either feed on grasses growing in relative density in the mountain, where it would be difficult to observe them or out of the catchment entirely. DISCUSSION Current size and distribution of elephant groups

The results obtained from both transect and aerial surveys indicated that the numbers and group size of elephants resident in the Hoanib catchment area varied both seasonally and annually, confirming previous observations of Viljoen (1988) and Lindeque & Lindeque (1991). Areas of relatively high human population (approximately 3500 people) in the middle of the catchment separate the eastern and western populations. The villages of Sesfontein, Warmquelle, Khowarib and several smaller settlements form an effective barrier to elephant movement through the middle of the catchment. Annual fluctuations in elephant numbers appear to be dependent on the distribution and quantity of rainfall within and outside the catchment. In addition, seasonal variations in numbers and distribution appeared to be linked to the relative abundance of food and disturbance factors caused by human populations. In the ECA, greater numbers of elephants were observed during the wet season and for several months after the rains. This was probably linked to water and food availability in the veld at this time. In October 1999, elephant were observed to move within 24 hours of the first rains of the wet season, from the dry Hoanib riverbed to the mountains in the southeastern section of the catchment area (approx. 30-50 km) . Lindeque & Lindeque (1991) reported similar movements of elephants in response rainfall in Etosha National Park and Damaraland. However, it is unclear what the stimulus for this rapid movement was. Some of the Commiphoria spp. sprout shoots soon after rains but the immediate movement of the elephants would not give the plants long enough time to sprout. Certainly, water would not be a limiting factor in the mountains immediately after rains, but the shallow pools in the rocks would only last for a short period. Elephants were not observed in the southeastern mountain ranges at any other time during this study. It was observed both in this study and by Viljoen (1988), that when grass and browse are available in areas away from the rivers during the wet season,

313

elephants in the eastern catchment spent most of their time dispersed throughout the veld and in the mountains. However, during the hot-dry season, male elephants were regularly observed in the dry riverbeds seeking shelter from the heat under large Faidherbia albida trees. When the f albida fruit matures (August/September); increased numbers of elephants (as well as other wildlife) were observed in the riverbed. The f albida seed maturation occurs later in the WCA (towards the end of the hot-dry season); however, it causes a similar aggregation of elephants to that described in the ECA. This type of feeding aggregation of elephants during times of local food abundance has been reported by a number of authors throughout Africa (Viljoen 1988; Barnes 1983; Western & Lindsay 1984). Elephants in this area tended to remain in the riverbeds during the hot-dry season. At the onset of the wet season, they moved back onto the plains to graze and browse on the newly germinated and recently sprouted vegetation. During the cold-dry season, between 14 and 16 elephants (individually identified) were permanently associated with the western Hoanib River, in particular the fresh-water springs at Dubis (22 km west of Sesfontein). The number of elephants increased to an observed maximum of 42 just after floods when fresh water was available and vegetation became more plentiful along the riverbed. Flooding of the lower section (western section/floodplain) of the river provided grazing in areas that are normally devoid of edible vegetation. It also provided fresh drinking water in close proximity to the grazing. Without the regular flooding events, little edible vegetation would be available in this area, with the nearest fresh-water spring approximately 30 km from the floodplain. The flooding of the western section of the river resulted in some elephant moving westward from Dubis toward the floodplain (Fig. 2.). Other elephants had been observed to move from the Hoarusib River to the Hoanib River floodplain at this time. Viljoen (1988) and others observed large numbers (up to 25 individuals) of elephant crossing between the two rivers during the wet season, but during this study no such mass movements were observed. Occasionally, family groups or lone adult males moved between rivers but the group sizes were considerably smaller than those observed by Viljoen (1988) . While the exact number of elephants in the WCA varied both seasonally and annually, the total

314


numbers of elephants observed during this study was approximately the same as those recorded by Viljoen (1988) . Viljoen reported 75 desert-dwelling elephants in the Hoarusib, Hoanib and Uniab River catchments in 1981/82, with approximately 45 in the western Hoanib River catchment. During this study a maximum of 42 elephants were observed in the WCA. It would appear that the total number of the desert-dwelling elephants has remained stable for the last 20 years. The reasons for this stable population is not certain, but it is possibly linked to high mortality rates caused by the adverse climatic conditions (Viljoen 1988 reported 100% calf mortality) and the limited amount of browsing and grazing area. The elephants have recently expanded their ranges, spending less time in the Hoanib River and more in the Hoarusib River compared to that observed during Viljoen' s study. The local residents of Purros confirmed this observation. Temporal change in average group size

The historical data obtained from MET and Viljoen (1988) indicated that the average group size of elephants observed in the Hoanib catchment area had decreased since 1981. Viljoen (1988) theorized that the breakdown of groups was the result of dispersal of large feeding aggregations, but that groups did not decline below a certain minimum size. Further, he postulated that these minimum size groups remained constant even during periods of extreme food and water shortage. The decrease in group size was most marked in the ECA where the average group size had fallen from 11.14 (1984) to approximately 2.00 (1992), and currently 3.82 (2000). While data for the ECA were not as extensive as for the WCA, a decline in group size was apparent. According to Viljoen (1988), poachers shot sixty elephants (33 % of the estimated population) in the ECA between 1980 and 1982. Under the stress of this kind of poaching, elephants tend to form larger group sizes (Laws et al. 1975; Eltringham, 1977; Abe 1982; Poole 1989) and this was reflected in the historical observations. Since that time, poaching and its associated stress have been reduced and, with an increased tolerance for elephants displayed by the communities living in the area, group sizes have again decreased. From 1981 to 2000 the average group size of elephants in the WCA varied in the range of 1.00 to 9.29. Overall, there has been a decrease in average group size from 4.76 to 2.26 in this period, with a most significant decline between 1981 and

1991. This decrease in group size may be linked to a decrease in disturbance and poaching pressure. In the WCA a seasonal trend in average group size was observed with a tendency for smaller group sizes during the cold-dry season in contrast to aggregations of groups during both the hot-dry and wet seasons. This increase in average group size is possibly due to an increase in seasonal availability of food. The cold-dry season break-up into smaller units would reduce intra-group competition under conditions of food shortage (DouglasHamilton & Douglas-Hamilton 1975; Barnes 1983; Western & Lindsay 1984; Viljoen 1988). During this study, the WCA males were observed singly or in pairs but at no time were males in groups greater than two. This result differed from those reported by Viljoen (1988) who observed groups >2 in 29.2% of his cold-dry season observations (1980-83). In contrast to the western males, 20% ofrecords for the ECA males during this study were observed in groups larger than two. The eastern elephants are subjected to greater human disturbance and hunting pressures than those of the west, which is a possible reason for the larger aggregations of adult males. The WCA adult males had much larger home ranges than the adult females and only two adult males were observed to be permanently resident in the western section of the river. All other males were much more transitory. Social interactions

Family unit inter-relationships between adult females and their older offspring were extremely difficult to identify and monitor. Adult females formed loosely bonded groups, not forming large family units as has been reported from other parts of Africa (Douglas-Hamilton & Douglas-Hamilton 1975; Leuthold 1976; Leuthold 1977; Moss 1982). Four of these small family groups were identified and monitored. It was not uncommon to record several small family units together one day and then separate the next. Viljoen (1988) reported similar loosely associated groups but within recognized clans which supports the hypothesis by Lindeque & Lindeque (1991) that the elephants of the catchment are a 'skeletal' population, limited in density and group size by extreme aridity. There was a spatial separation of groups in the western Hoanib. Some gro ups occupied the floodplain during the wet season and others that were more permanently associated with the wetlands around Dubis (approximately 50 km


upstream). Little interaction between these two groups was recorded. However, the behaviour of adult female groups towards each other on meeting was neutral or even at times amicable, but the elaborate social greeting and interactions described by other authors (e.g. Moss 1982) were not observed during this study. ACKNOWLEDGEMENTS

We thank Mary Seely and the staff of the Desert Research Foundation of Namibia for their help and assistance throughout the study. Thanks are also due to the Ministry of Agriculture, Water and Rural Development for continued support, and the Ministry of Environment and Tourism for permission to conduct the study in northwestern Namibia. Our appreciation goes to Sida for funding the study, and to the NGOs and line ministries who provided us with invaluable support. We are especially grateful to the communities in the Hoanib River catchment or their cooperation REFERENCES

ABE, E. 1982. The status of elephan ts in Uganda: Queen Elizabeth National Park. Pachyderm 15, 49-52. ALTMANN, J. 1974. Observational study of behaviour: sampling methods. Behaviour 49, 277-67. BARNES, R.F.W 1983. Effects of elephan t browsing on woodlands in a Tanzanian National Park: measurements, models and management. Journal of Applied Ecology 20, 521-540. BECKER, T. & JURGENS, N. 2000. Vegetation along climate gradients in Kaokoland, North-West Namibia. Phytocoenologia 30, 543-565. CARTER, L.A. 1990. The Wildlife Survey of Skeleton Coast Park, Damaraland and Kaokoland, North West Namibia, May/June 1990. Report to the Commission of the European Communities, Contract 946/89-48, Wind· hoek, Namibia. DE VILLIERS, P.A. 1975. Lugsensus - Kaokoland. Unpublished report, Department of Cooperation and Development, Windhoek, Namibia. DOUGLAS-HAMILTON, I. & DOUGLAS-HAMILTON, 0 . 1975. Among the Elephants. Collins and Harvill Press, London. ELTRINGHAM, S.K 1977. The numbers and distribution of elephant Loxodonta africana in Rwenzori National Park and Chambura Game Reserve, Uganda. East African Wildlife Journal 15, 19-39. HILTON-TAYLOR, C. 1994. The Kaokoveld. In: Centres of Plant Diversitt;. A Guide and Strategy for Their Conservation, WWF & IUCN, pp. 201-203. IUCN Publication Unit, Cambridge, U.K HUTCHINSON, P. 1995. The climatology of Namibia and its relevance to the drought situation. In: Coping With Aridity, (eds) Namibia Economic Policy Research Unit (NEPRU), pp. 17-37. Brandes and Apsel/ NEPRU, Windhoek, Namibia. JACOBSON, P.J, JACOBSON KM & SEELY M.K 1995.

315

Ephemeral Rivers and Their Catchment: Sustaining People and Development in Western Namibia. Desert Research Foundation of Namibia, Windhoek, Namibia. JACHMANN, H.1991. Evaluation of four survey methods for estimating elephant densities. African Journal of Ecology 29, 188-195. JOUBERT, E. 1972. Voorgestelde Damaraland Wildtuin. Unpublished report, Depatment of Agriculture and Nature Conservation, SWA [Namibia]. LAWS, R.M. 1970. Elephants as agents of habitat and landscape chan ge in East Africa. Oikos 21, 1-15 LAWS, R.M., PARKER, l.S.C. & JOHNSTONE, R.C.B. 1975. Elephants and Their Habitats. Claredon Press, Oxford. LEGGETT, KE.A., FENNESSY, J. & SCHNEIDER, S. 2001. Rainfall, water sources and water use in the Hoanib River catchment, northwestern Namibia, In: DRFN Occasional Paper 15: 37-75. Windhoek, Namibia. LE ROUX, J. 1978. Damaraland lugsensus 15 Oktober 18 Oktober. Unpublished report, Damara Verteenwoordigende Owerheid, Windhoek, Namibia LEUTHOLD, W 1976. Group size in elephants of Tsavo National Park and possible factors influencing it. Journal of Animal Ecology 45, 425-439. LEUTHOLD, W 1977. Spatial organisation and strategy of habitat utilization of elephants in Tsavo National Park, Kenya. Zeitschrift fii.r Siiugetierkunde 42, 359-79. LINDEQUE, M. & LINDEQUE, P.M. 1991. Satellite tracking of elephants in northwest Namibia. African Journal of Ecologi; 29, 196-206. LOUTIT, R. 1993. Aerial survey of Kunene district. Unpublished data, Ministry of Environment and Tourism, Windhoek, Namibia. LOUTIT, R. 1995. Elephant survey in Kunene district. Unpublish ed data, Ministry of Environment and Tourism, Windhoek, Namibia. MARTIN, R.B. 1978. Aspects of elephant social organisation. The Rhodesian Science News 12184--187. MINISTRY OF ENVIRONMENT AND TOURISM, 1984--1995. Ground counts of wildlife in Damaraland and Kaokoland. Unpublished da ta, Ministry of Environmen t and Tourism, Namibia. MOSS, C.J. 1982. Portraits in the Wild: Behavior Studies of Eastern African Mammals. University of Chicago Press, Chicago, U.S.A. MOSS, C.J. & POOLE,J.H.1983. Relationships and social structure in African elephants. In: Primate Social Relationships: An Integrated Approach, (ed.) R.A. Hinde, Chap. 13, pp. 314--325. Blackwell Scientific Publications, Oxford, U.K NORTON-GRIFFITHS, N. 1978. Counting Animals, 2nd edn. African Wildlife Foundation, Kenya. OWEN-SMITH, G.L. 1970. The Kaokoveld -An Ecological Base for Future Development and Planning. Pim, Pinetown, South Africa. OWEN-SMITH, G. 1996. The Kaokoveld: southern Africa's last wilderness. In: Namibia Environment, Volume 1, pp. 62-65. Ministry of Environment and Tourism, Windhoek, Namibia. PENNYCUICK, C.J., SALE, J.B., PRICE, M.S. & JOLLY, G.M. 1972. Aerial systematic sampling applied to census of large mammal populations in Kenya. East African Wildlife Journal 10, 175-191. POOLE, J.H. 1989. The effect of poaching on the age

316


structure and social and reproductive patterns of selected East African elephant populations. In: Ivory Trade and the Future of the African Elephant, Vol. 2, Section 5, 43 pp. Report by Ivory Trade Review Group to CITES. POOLE, J.H.1996. The African elephant. In: Studying Elephants, (ed.) K. Kangwana, pp. 1-8. AWF Technical Handbook Series No. 7, African Wildlife Foundation, Nairobi, Kenya. SANTIAPILLAI, C., CHAMBERS, M.R. & ISHWARAN, N. 1984. Aspects of the ecology of the Asian elephant in the Ruhuna National Park, Sri Lanka. Biological Conservation 29, 47-61. SPECIAL SUPPORT SERVICES 1999. Aerial Census of Wildlife in Northern Namibia. Report of the Ministry of Environment and Tourism, Namibia. SUKUMAR, R. 1989. The Asian Elephant: Ecology and Management. Cambridge University Press, Cambridge, U.K. VILJOEN, P.J. 1987. Status and past and present distribution of elephants in Kaokoveld, South West/Namibia. South African Journal of Zoologi; 22: 247-257. VILJOEN, P.J. 1988. The ecology of the desert-dwelling

elephants Loxodonta africana (Blumenbach, 1797) of western Damaraland and Kaokoland. Ph.D. thesis, University of Pretoria, Pretoria, South Africa. VILJOEN, P.J.1989a. Spatial distribution and movements of elephants (Loxodonta africana) in the northern Namib Desert region of the Kaokoveld, South West Africa/Namibia. Journal of the Zoological SociehJ of London 219: 1-19. VILJOEN, P.J. 1989b. Habitat selection and preferred food plants of desert-dwelling elephant population in the northern Narnib Desert, South West Africa/ Namibia. African Journal of Ecologi; 27: 227-240. VILJOEN, P. J. & BOTHMA, J. DU P. 1990. Daily movements of desert-dwelling elephants in the northern Namib Desert. South African Journal of Wildlife Research 20: 69-72. VISAGIE, G.P. 1977. Lugsensus - Damaraland. Unpublished report, Department of Cooperation and Development, SWA [Namibia]. WESTERN, D. & LINDSAY, WK (1984) Seasonal herd dynamics of a savanna elephant population. African Journal of Ecologi; 22: 229-244.