Rainfall

The drying out of floodplain habitats probably has the greatest influence on the abundance of all four species. The total area of wetland habitats in Caprivi is about 3,000km2 but it would be a mistake to regard this as a constant. In times when the cumulative deviations from the mean rainfall are in a deficit, the real amount of habitat available to reedbuck, waterbuck, lechwe and puku may be much reduced. Since 1994 such a situation has pertained (Figure19).

A surplus in the accumulated rainfall need not necessarily produce a linear increase in population growth rates – it should rather be seen as the removal of a primary limiting factor. However, a deficit in the accumulated rainfall is likely to be the primary limiting factor for reedbuck, waterbuck, lechwe and puku. All management efforts directed at secondary factors are unlikely to surmount this fundamentally negative effect.

Given that the rainfall regime is favourable (i.e. in a period of accumulated surplus), management efforts directed at a number of other potentially limiting factors may enhance population growth – e.g. control of illegal hunting and fire.

Competition with domestic livestock

throughout their range, except within the State Protected Areas, reedbuck, waterbuck, lechwe and puku are forced to compete with domestic livestock (Figure 16). The total area of floodplain habitat within the protected areas is about 500km2 (Table 6)), so that in fivesixths of their potential range, competition and range degradation is a major limiting factor. Waterbuck, in particular, tend to avoid overgrazed areas. Child and von Richter (1969) argued that the poor condition in lechwe and the low numbers of waterbuck and puku were indicative of a decline in habitat quality.They felt that of the four species, puku had the smallest amount of ideal habitat in the Chobe system.

Loss of habitat

Of the original area of floodplain habitat in the Caprivi (some 4,500km2), it is estimated that about one-third has been cleared for agriculture. If the clearance continues at a rate corresponding to the human population increase, it will not take long before the only remaining pristine habitats are the 500km2 in protected areas.

Fire

The annual practice of burning large areas of the floodplains in the Caprivi is like to further depress the carrying capacity for the wetland grazers. Reedbuck, in particular, avoid burnt areas.

Minimum viable populations

Waterbuck and puku population levels may have dropped below that threshold at which the population is sustainable –even if fully protected and given favourable habitat conditions. There is always the possibility that dispersal from the larger Botswana populations in years of high rainfall could re-establish populations in the Caprivi. However, pro-active reintroductions of twaterbuck and puku might bring about the desired objective more quickly.

Illegal hunting

This factor is everpresent and requires to be held to a level at which offtakes from the species populations are sustainable i.e. a maximum of about 9% per annum.

Veterinary fences

The international veterinary cordon fence along the southern boundary of the Caprivi prevents seasonal movements of lechwe along the Kavango River between Botswana and Namibia (Figure 10b). In the long run this could result in a population crash in the small lechwe population of Mahango national park and would remove the possibility of the species re-establishing itself. The north-south part of the same veterinary fence which separates Khaudum national park and Nyae Nyae conservancy from Botswana acts against the establishment of permanent reedbuck populations on the Namibian side of the border.

Predation

Lechwe are a favoured prey species of lions and leopards. However, it is doubtful whether this factor could result in a significant population decline.

Inappropriate land use planning

At a higher level of analysis, inappropriate land use planning may be the most significant cause for the poor conservation scenario. The fact that there are no protected areas in any of the Zambezi floodplain vegetation types (which constitute nearly one-third of the suitable habitats for wetland grazers) and the fact that the existing protected areas are islands in a sea of humans, does not augur well for optimum land use in the Caprivi or for achieving regional conservation goals such as major transfrontier conservation areas. What has happened is large historical. The question of what can be done about it is the more interesting one. Notwithstanding the past, the opportunity exists to form larger co-managed areas of land under wildlife in the Caprivi – provided suitable institutions can be developed.