The timing and intensity of the first summer rains in the Kalahari basin are highly variable between years. Avian migrants to the area follow two principal strategies. Species arriving before November typically do so before significant rain can be expected and do not use ecological conditions as a proximal cue to time arrival; their arrival was unaffected by the failure of the early rains in 1994. Species arriving after mid-November respond to the timing and extent of the early rains and were progressively more delayed in parallel to a cumulative deficit in rainfall during the early part of the 1994 wet season. The second strategy results in erratic occupation of parts of the nonbreeding range, so that during drought years, rain-dependent, late-arriving species may remain absent from the Kalahari basin, complicating the assessment of the "effective" size of their nonbreeding range.