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Nomadic larks in the semi-arid Nama-Karoo, South Africa, depend on patches of temporally suitable habitat for breeding. These patches occur where rain has recently fallen, where there has been growth and seeding of grasses, and where invertebrates are locally abundant. They are also attractive to domestic livestock which may constitute a threat to successful breeding by the larks. Since rainfall in the Nama-Karoo is unpredictable in time and space on a regional scale, it is difficult a priori to select protected areas for such nomadic birds. As a first approach, we present a spatio-temporal model for estimating the survival of flocks in relation to different configurations of protected areas. The results show that neither one large protected area nor a high number of small protected areas provide the optimal solution. This is due to the impact of various spatial effects which affect the probability of a flock finding a suitable breeding area. These effects are identified and discussed. Furthermore, we are able to reproduce and explain the present spatial abundance of the larks on a regional scale with our model. The model is intended to complement and define the field studies needed to determine practical parameters more precisely.