Seasonal variation in hematocrit levels of Amethyst Sunbirds (Chalcomitra amethystina) over an altitudinal gradient

Abstract

The distribution range of Amethyst Sunbirds (Chalcomitra amethystina) within southern Africa includes an altitudinal gradient from the Drakensberg to the coast of KwaZulu-Natal. We expected that, over this altitudinal gradient, Amethyst Sunbirds would exhibit variation in hematocrit levels pre-and post-acclimation, as well as seasonally. Sunbirds from three locations; Underberg (1,553 m asl), Howick (1,075 m asl) and Oribi Gorge (541 m asl) were used for this study. Birds were then acclimated at 25°C for 6 weeks on a 12L:12D cycle. Hematocrit levels were taken pre-acclimation and prerelease. We found significant variation in hematocrit levels during summer, but surprisingly little variation during winter. Season and location had a significant combined effect on pre-acclimation hematocrit levels of Amethyst Sunbirds. Underberg and Howick had greater values in summer compared with winter whereas the converse was found in Oribi Gorge. In contrast, season and location had no significant combined effect on post-acclimation hematocrit levels of Amethyst Sunbirds, with post-acclimation levels similar for the three sites irrespective of season. This study emphasizes the need to understand flexibility in hematocrit levels and acknowledge seasonal and altitudinal differences within a species.