Conservation biology of the Gaboon Adder (Bitis gabonica) in South Africa

Abstract

From 2005-2007, I studied the ecology of Bitis gabonica, a terrestrial forest viperid that occurs in subtropical northeast extremes of South Africa. I monitored ten individuals (six males and four females) using radiotelemetry inside the iSimangaliso Wetland Park in KwaZulu-Natal. I used two different home range estimators to analyze space use among individuals; minimum convex polygons (MCPs) and kernel density contours (KDs). MCPs averaged 28.58 ha (42.48 ha for males, 7.72 ha for females) and ninety-five percent kernel density contours (KDs) averaged 28.92 ha (42.65 ha for males, 8.32 for females). Fifty percent KDs (core areas of activity) averaged 6.74 ha, with the mean male core activity centre almost five times greater than that of females. Telemetered B. gabonica were highly sedentary, especially during winter when individuals remained at single localities for extended periods (max. 87 days). Activity peaked for both sexes at the onset of the breeding season, with individuals averaging a movement distance of 598 m during March. At sites where telemetered B. gabonica were observed, I measured a suite of sixteen critical habitat variables and then used MANOVA to test for differences among habitat characteristics for several different categories (season, sex and habitat selection). Bitis gabonica habitat preferences were strongly influenced by season, with individuals selecting open-canopied areas during cooler months, presumably because the forested habitat individuals utilize the rest of the year is not adequate for the species’ thermoregulatory requirements during winter. Female B. gabonica used slightly less shrubby microhabitats than males. The variability found between B. gabonica sites and random sites was primarily explained by features that constitute the understory, with snake sites having denser understory structures and being located closer to woody vegetation. This type of “thicket” microhabitat is important for the protection, thermoregulation and food acquisition requirements of Gaboon Adders. Among telemetered B. gabonica, feeding activity varied between seasons, with individuals spending long periods of time at single localities in an ambush position, especially during summer. Snakes exhibited strong ambush site fidelity, often remaining immobile for weeks at a time. Sites where ambush behaviour was observed were frequently in close proximity (< 1 m) to game trails created by antelope, and new B. gabonica feeding records from my field work (e.g., Red Duiker; Cephalophus natalensis) indicate individuals may target large prey (close to their own body mass) when available. The unique morphological adaptations of B. gabonica are discussed in the context of foraging ecology. Ecological research from this study, coupled with new molecular data that shows South African and central African B. gabonica are genetically similar, suggests the South African B. gabonica population’s conservation status is better than what was previously assumed. However, long-term protection and management of the coastal dune forest corridor (found primarily inside the iSimangaliso Wetland Park) is needed for a viable, local B. gabonica population. A handbook is provided specifically for Park staff which summarizes the ecology and threats to B. gabonica, and provides up-to-date management decisions on controversial protective measures (e.g. translsocation).