ECOLOGICAL ISOLATION IN GREYWING AND REDWING FRANCOLINS

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Abstract
The graywing francolin Francolinus africanus and redwing francolin F. levaillantii are closely related, of similar size and live in superficially similar habitats. Their ranges overlap, and ecological isolation was studied in the Natal Drakensberg where partial sympatry occurs. In the study area, graywing francolins occurred above 1840 m a.s.l. [above sea level] and redwind francolins below 2450 m a.s.l. Within the zone of sympatry there was a partial polarization with graywing francolins in sparse, short grass at high elevations, and redwing francolins in denser, taller grass at low elevations. The abundance of the birds did not differ in relation to slope, aspect and vegetation type. The principal diet of both species was composed of the corms and tubers of grassland geophytes. The birds ate the same species of geophytes but in different proportions. Graywing francolins are small volumes of food of apparently high nutritive value, while the reverse applied to redwing francolins. Within the zone of sympatry the 2 birds are apparently not isolated ecologically, but are in partial competition.

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