LIMPOPO VALLEY ELEPHANT RESEARCH PROJECT
Elephants in the Systems Context
Elephant numbers are increasing in many parts of their range. In all of these areas, changes in habitat structure and composition are being observed. Elephants are commonly perceived as the major agents driving these changes. This contention is based on two observations. Firstly that elephants push over, ring bark and break branches from trees, and in so doing frequently kill them, and secondly that in areas where there are elephants, many dead trees and large quantities of dead wood occur. These observations have led to a widely held perception that elephants are a keystone species that determine the structure and composition of their habitats. This contention has in turn lead to claims that elephants at high numbers (high is not defined) pose a threat to biodiversity in the conservation areas in which they occur. In support of this contention, examples of species loss from elephant habitats, and perceived effects of changes in structure on the abundance of many other species are presented. These contentions have lead to widespread calls for culling of elephant populations to be implemented to prevent the loss of biodiversity. However there is also a widely held contrary view that contends that the data in support of the contention that elephants are a keystone species are lacking, and that the reduction of elephants to low numbers will not have the desired effect of preventing change in the system. In support of this, an emerging body of evidence is cited, that suggests that the observed changes are a consequence of the combined effects of several abiotic and biotic influences.
Emerging from discussions between wildlife managers on the effects of limiting elephant numbers and casual agents of change in elephant habitats is a realization that there is a severe lack of knowledge concerning four main issues. Firstly how elephant populations are limited; secondly, the relative importance of other herbivore species, climate and fire as determinants of systems structure, composition and dynamics; thirdly, how coexistence between elephants and trees was achieved in the past; and fourthly, how vegetation structure and composition influences overall biodiversity.
This research program aims to address all four of these areas of knowledge.
Research on the Central Limpopo River Valley elephant population
Research on elephants in the central Limpopo River Valley has a long history. After an absence of at least 50 years and probably closer to 100, elephants were again observed in the region in the early 1940’s. Numbers were recorded intermittently until the early 1970’s when a concerted effort was made to determine numbers and the range of the elephants in the region. Aerial counts in the Northern Tuli Game Reserve established that there were between 200 and 700 elephants that moved in and out of the area. Where they went to or came from was not established. At this time change in the structure of the vegetation was first noticed and a research project to establish the impact of elephants on the vegetation was carried out in 1978. Seventy permanently located monitoring transects were established in the area during this study, and these were re-sampled three times between 1978 and 1998. Fifty Elephants were introduced to the Venetia-Limpopo Nature Reserve in South Africa in 1992. The impact of these elephants was studied in 1997. In 1998 a study to determine the range and social structure of the population was began. This study has just been completed. Censuses of the entire area determined that there were 1400 elephants in the region, distributed mainly within the core area as defined below (Figure 2).
Figure 2. Distribution of elephant herds during the aerial censuses of August 2000 (pink squares) July 2001 (green dots) and October 2004 (blue triangles). The size of the symbol is proportional to the number of elephants in the group.
This study also showed that group sizes fluctuate in response to rainfall, being larger when rainfall is higher. Numbers in the central Northern Tuli Game Reserve (NTGR) area were shown to change from month to month and were different in the same month of different years. Whilst these data indicate that movement into and out of the NTGR occurs, the pattern of movement and what influences it is not known.
In November 2004 four elephant cows from four different family units along the Majale River that bisects the NTGR were collared with satellite collars as a pilot study to ascertain how elephants were moving in the area and what factors were influencing movement. Preliminary findings from this study indicate that social factors are extremely important in determining range use, and have shown that collaring of additional animals (both cows and bulls) is required to properly establish how social factors influence range use and ultimately the demographics of elephant populations.
Aims and Objectives
The overall objective of the research program is to establish how elephants and trees coexisted in the past, and what the effect of elephants and other herbivores on biodiversity was. The specific aims are:
- To determine how elephant populations are limited
- To determine the influence of elephants, each of the other large herbivore species, and climate on the structure, composition and dynamics of the vegetation
- To determine how elephants and trees coexist in time and space, and what the spatial and temporal scales are for the Central Limpopo River Valley .
- To determine how the composition and structure of vegetation influences overall diversity
Each of these specific aims will be addressed by one or two separate research projects.
The determinants of movements, range use and demographics of elephants
The Central Limpopo River Valley Elephant Research Project has raised several questions as to what factors govern the movements of the elephants within the region and what the extent of these movements are between the various sub populations. By determining the factors controlling the movements of the various groups we will be one step closer to solving the problem of elephant management. These factors can however only be determined by tracking the movements of the various groups over an extended period. Due to the size of the area this can only be achieved through satellite radio collaring various groups throughout the study area. A follow-up project is planned for 2005 in which various groups throughout the region will be collared and monitored for an extended period of time. With this in mind four elephant cows have been collared within the Northern Tuli Game Reserve during November 2004. The project will form part of the Elephants in the Systems Context Research Program under the supervision of Bruce Page at the University of Natal .
Hypotheses to be Tested
- The distribution of surface water for drinking is the major determinant of the area of the total seasonal, annual and inter-annual home ranges.
- Within a specific distance from accessible drinking water, the spatial and temporal pattern of distribution of patches of vegetation of different nutritional quality relative to the location of water and each other, determines overall feeding rates, rates of movement, and the extent of the seasonal, annual and inter-annual home ranges. In poor quality habitat individuals and groups move more.
- Survival of individuals in family units depends on the spatial and temporal pattern of distribution of patches of vegetation of different nutritional quality relative to the location of water and each other. Where the nutritional quality food is low survival is low, and where the best quality food is far from drinking water, survival is low.
- Family units of female with high social ranking have access to habits of high nutritional quality, with adequate shade, close to surface water. In times of nutritional stress the overlap in range of family units of lesser social status with the ranges of fu’s of high status reduced and these fu’s are forced to utilize habitat of poorer nutritional quality and access to shade and/or are required to move further to access both water and high quality habitats. A consequence of this is that bond group and clan ranges increase in size during in periods of nutritional stress.
- Survival of all individuals, particularly juveniles, sub adults and lactating females is lower during periods of stress in family units of lower social status.
- Human disturbance influences rates of movement and home range size and survival.
Aims and Objectives
The broad objective is to establish what environmental and social factors influence movements and the occupancy of different habitats.
The specific aims are
- To determine the seasonal distribution of available surface water for drinking in the CLRV.
- To determine intra- and inter- seasonal temporal and spatial patterns in variation in nutritional quality between different habitat (landscape) types, and within the same habitat type in the current range of the CLRV elephants
- To determine the different individual and group activities in the different habitat types.
- To determine the social status of a selection of males and different family units in the CLRV population
- To determine the rates of movement of males and females with different social status in different seasons in different habitat types.
- To determine how nutritional status in different seasons and in the same season in different years, and the social structure influences the fission and fusion of family units and bulls into groups of different sizes.
- To determine the frequency of return visits to particular points and areas within particular habitat types, and the duration of occupancy of these areas by different family units, clans, bond groups, bulls and bull groups of different sizes and how this is influenced by nutritional quality and social status of the groups or individuals involved.
- To determine rates of survival of individuals within family groups and bulls different social status.
GIS and Baseline Data Collection
The first phase of this project will involve establishing a GIS of the region that will be used in the other three projects as well, and will also provide a basis from which to plan the development of the TFCA.
Satellite imagery will be used to develop a vegetation map of the region. This will be ground truthed using data collected in Projects 2 and 3.
All of the usual layers for vegetation, topography, surface water, buildings, roads, land use, settlements, power lines, telephone towers, etc will be obtained as part of this project.
Determinants of Movements and Range Use (Occupancy and Activities in Different Habitats)
Twenty elephants will be fitted with satellite collars. Four females from different family units and two males will be collared with satellite collars in the NTGR (in addition to the four females already collared). Two of these will be collared on the Shashe River and two on the Motloutse River . Four females and one male will be collared in the area between Bain’s Drift and the Motloutse River . One female and one male will be collared in Zimbabwe , one female and one male in South Africa , one female in the Letsibogo Dam group in Botswana .
Two fixes per day at a 12-hour interval will be collected for a two-year period. In addition in mid summer (late December / early January) and late winter (October) intensive data will be collected at 3-hour intervals for 10 days to ascertain rates of displacement.
Each of the 20 collars will be fitted with a VHF transmitter. These will be used to locate one or more of the herds on a daily basis. This herd will be followed without disturbance and the following information recorded. (i) Position whenever direction of movement changes, but at least half hourly, (ii) dominant activities of the group whenever the group activity changes, or at least at half hourly intervals, (iii) the size of the group, and its age and sex structure by photographing as many individuals with a digital camera as possible on each encounter. (iv) interactions between individuals in the group to determine dominance within the group (v) association with other female groups. In addition for five days each month each section of the range (NTGR, Motloutse-Bains Drift, Zimbabwe ) will be surveyed to locate the positions of other fu’s and males in the population.
The positional data from collared animals and from the monthly surveys will be supplemented with data collected by tourists who own a digital camera and GPS.
In addition two total counts each year will be carried out for two successive years, one in mid winter (July/August) and one in mid summer (December/January), to determine the overall spatial distribution of the population in different seasons.
Seasonal variation in the nutritional quality of different habitats will be determined by (i) monitoring daily rainfall at several different stations throughout the study area, (ii) monitoring phenological status at several stations in different landscape types throughout the study area (iii) topographic overlays, (iv) the soils maps, and (v) chemical analysis of plant material in each habitat. These data will all be related in a GIS to NDVI’s for end of winter (Sept/Oct), beginning of summer (Nov), end of summer (Feb/Mar), and beginning of winter (May/Jun). (A separate 4 th year level project in GIS is also being run to ascertain if an index showing differences in quality rather than biomass can be derived.)
Surface water will be mapped twice per year at the end of summer (December/ January) and the end of winter (September/ October).
The age and sex structure of each of the family units with collared elephants will be ascertained by intensively photographing animals using a digital camera, and then using an expert system linked to a database containing the photographs to construct a family tree of the particular family unit. Animals will be aged using diagrams of relative size at different ages, the general appearance of the animal and associated offspring, and assigned to 10 age classes (infants (1-2 years old), weaning calves (3 - 4), juveniles (5 - 7), sub adults (7 - 10), young adults (10 - 15), maturing adults (15 - 25), prime adults (25 - 35), mature adults (35 - 45), old reproductively active adults (45 - 50), old reproductively inactive adults (50 - 60)). Careful note will be made of births over the five-year period. Deaths will be detected by noting missing animals, and from reports of dead animals from residents in the area.