There are two basic strategies for coping with life in the desert. The first involves withstanding the extreme conditions using behavioural or physiological tactics. The second strategy is to be a migrant and to opportunistically or seasonally move to where the necessary resources are. Nomadism, i.e. the opportunistic and irregular movements from resource-poor to resource-rich patches, is a tactic that birds, with their mobility, can use, and it is explored by W.R.J. Dean in this volume. For many bird species, such movements between habitats or across landscapes to find patches of resources are essential for their continued existence. The relationship between climate, habitat and movements in the avifauna of arid and semi-arid regions and the advantages and disadvantages of a seasonally migratory or opportunistically nomadic lifestyle are elucidated.