THE PROJECT
I have set up the Okavango Buffalo Research Project to collect data for my PhD with the University of Bristol, in association with the University of Botswana.
African buffalo were selected for this, the first single species herbivore study in the Delta, because they are thought to play vital role in the ecosystem. Buffalo are large animals that can form herds of several thousands. They are also one of the most numerous animals in the Delta, with the population estimated at 60,000 individuals, representing 39% of the total herbivore biomass of the Delta (Bonyongo, 2004). These factors combine to suggest that the African buffalo is a keystone species, and any fluctuations in their numbers could have strong repercussions for the rest of the ecosystem.
Very little is known about the Delta’s buffalo population and much of that knowledge is anecdotal. My project is using satellite-enabled GPS collars from Televilt (Sweden) to record data from individual collared cows in different herds. These collars have been programmed to take a GPS fix every hour for the duration of the study. Every ten hours, these fixes are sent to a server in Sweden via satellite then uploaded onto the internet so that I can access the information. This means that I can monitor the movements of the herds almost continuously.
The collars emit a VHF (Very High Frequency) signal that allows the herds to be tracked using conventional telemetry equipment. The herds are found from the air using a light aircraft to obtain estimates of herd numbers. I also track the herds from the ground approximately once a month to ensure that the collars are working properly and that they are not causing any inconvenience to the cows bearing them. I then record information on the population dynamics (age and sex ratios) and on the body condition of the individuals. At this time I also collect faecal samples.
Often the herds are in habitats that make following them to collect observational data very difficult. The collars are programmed to record temperatures and degrees of activity (how much the collar moves over the time taken to obtain a fix). By combining distance and direction between points with activity levels, I can work out whether the animal was walking, resting or grazing at any given point. I use this information to identify areas that were selected for grazing and resting, and areas that were ignored, when the herd walked straight through without stopping.
I visit several of these areas in different habitat types to obtain information on the characteristics of those sites. This includes data on the vegetative species composition, percentage ground cover, biomass, the distance between tufts of grass, the canopy cover and the proximity to water. I identify which species of grass have been grazed and which have been ignored and take samples of the species in the area for analysis.
Data from the GPS collars are used to examine habitat use, home ranges and movement patterns. Fixes are overlaid on a vegetation map, as well as on satellite images to show which habitats are preferred and which are avoided. Estimates of home ranges are obtained from the GPS fixes, as are the different ways in which the herds move through their environment. They appear to move through small patches in relatively random ways, foraging as they go. They then move between patches of the same habitat type in a roughly linear fashion.
At the change of seasons, they move from patches of one habitat type to patches of another. They spend most of the wet season in areas dominated by mopane (Colospermum mophane) woodland and most of the rest of the year on islands and floodplains. Seasonal movements between these habitat types appear to be linear and occur over a short time period. I will develop a model to predict what triggers these relatively long distance movements, incorporating several factors such as water levels, forage quality and photoperiod.
This project will provide basic information on the ecology of the African buffalo in the Okavango Delta. The results of this study will help to identify the ecological requirements of buffalo in the Delta and anticipate the effect of any changes to the system on the buffalo population. With more research into the buffalo and their interactions with other species in the Delta, it will be possible to predict the impact of potential changes in the buffalo population on the entire ecosystem.