STRATEGIES, PUNCTUALITY OF ARRIVAL AND RANGES OF MIGRANTS IN THE KALAHARI BASIN, BOTSWANA

The timing and intensity of the first summer rains in the Kalahari bas in are highly variable between years. Avian migrants to the area follo w two principal strategies. Species arriving before November typically do so before significant rain can be expected and do not use ecologic al conditions as a proximal cue to time arrival; their arrival was una ffected by the failure of the early rains in 1994. Species arriving af ter mid-November respond to the timing and extent of the early rains a nd 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 ran ge, so that during drought years, rain-dependent, late-arriving specie s may remain absent from the Kalahari basin, complicating the assessme nt of the ''effective'' size of their nonbreeding range.