The use of VORTEX simulation models in a long term programme of re-introduction of an endangered large mammal, the Cape mountain zebra (Equus zebra zebra)

Of 20 groups of Cape mountain zebras re-introduced into new conservation areas 12 have increased, 6 have remained stable or decreased, and 2 went extinct. One of the main reasons for the poor performance of some of the groups was that insufficient numbers were re-introduced. In those cases where the population increased the mean number originally introduced was 15.1. This is significantly higher (P < 0.05) than the number introduced in the cases that failed to increase (8.1). This is in accord with other studies that have shown that the success of re-introductions is closely linked to the numbers of animals re-introduced. The mean percentage annual increase of the populations over the first three to five years after re-introduction (0.4%) was significantly (P < 0.05) lower than that over the subsequent 3 to 5 years (9.3%). This probably reflects the effects of capture stress, break up of family groups and adaptation to a-new environment. There was no significant relationship between maternal age and progeny sex ratio in Cape mountain zebra. A simulation modelling package, VORTEX was used as an aid to the management of Cape mountain zebra. Rates of population growth and sustainable harvests derived by means of the model were similar to those observed in the real population. The model is useful in analysing the poor performance of small populations re-introduced into new conservation areas, which may help to avoid unrealistic expectations on the part of new owners of mountain zebra herds and to underline the necessity of starting with a reasonable number of animals.