SUNBIRD MOVEMENTS - A REVIEW, WITH POSSIBLE MODELS

Based on current fieldwork, we propose four possible models to explain the winter influx of sunbirds which we have observed: the birds may b e (1) ''winter residents'', which move annually to a wintering area an d remain there; (2) ''shoppers'', which periodically investigate feedi ng areas within their home range and feed opportunistically where nect ar is most abundant; (3) ''tourists'', which successively visit a seri es of sites on a regular itinerary; (4) ''nomads'', which move unpredi ctably to new areas whenever food supplies decline. and have no home b ase. Current data on sunbird movements are reviewed, and in a few case s the winter resident model is unlikely, but generally it is not yet p ossible to eliminate any of the hypotheses. Moult cycles based on both field and museum studies may provide additional information, as movem ents are unlikely while active wing-moult is in progress; some species show interrupted wing-moult, which may be associated with long-distan ce flights.