ABIOTIC FACTORS AS PREDICTORS OF DISTRIBUTION IN SOUTHERN AFRICAN BULBULS

The closely related Black-eyed Bulbul (Pycnonotus barbatus), Red-eyed Bulbul (I! nigricans), and Cape Bulbul (I! capensis) occupy parapatric to locally sympatric ranges within southern Africa. We used a multiva riate discriminant function analysis to relate the South African distr ibution of these species at the resolution of a quarter-degree square of latitude and longitude to a suite of six environmental variables ex tracted from digital models. The analysis correctly classified the dis tribution of these species for 89% of the 1,426 squares analyzed. Sepa ration on the first discriminant function, which successfully characte rized the distribution of P. nigricans, was mainly by the coefficient of variation in mean annual rainfall and mean July minimum temperature . Separation on the second discriminant function, which successfully c haracterized P. capensis, was mainly by the ''normalized difference gr een vegetation index'' (derived from NOAA satellite scans). Using the standardized coefficients for the first discriminant function, a model generated to predict the distribution of P. nigricans at a finer geog raphic resolution within our Eastern Cape Province study area was 93% successful. The results suggest that the three species occupy distinct ly different habitats, as characterized by the suite of six environmen tal variables that we analyzed.