Morphological variation in the Common Fiscal Lanius collaris along an altitudinal gradient in southern Africa

Geographic variation among four Common Fiscal subpopulations along an altitudinal gradient in South Africa demonstrated significant variation of 13 morphological features and 38 skeletal characters. Common Fiscals were largest in cooler, less humid, more and areas and smallest in warmer, wetter, more humid localities, supporting Bergmann's Rule. Patterns of variation in morphology, anatomy and skeletal trends were significantly correlated with 11 climatic trends. Cardiopulmonary organ mass and blood haematocrit increased with altitude and reflected adaptations to low ambient temperatures and decreased oxygen pressures associated with high altitudes. These trends are concordant with those reported in various other avian species.