By Michelle Henley
South Africa’s white-backed vultures are now Critically Endangered, and their numbers continue to plummet. The main cause of this rapid decline are indiscriminate poisonings, where the birds are drawn to poisoned baits, use of vulture body parts in traditional medicine, and deliberate targeting by poachers, as the presence of vultures can alert authorities to illegally killed big game carcasses.
Since 2008, Elephants Alive has been monitoring trees and vulture nests on an annual basis, 226 trees used by raptors and white backed vultures as nesting sites to understand the influence of elephant impact on these sites. Recently we completed our annual survey.
We have found that the overall elephant impact was low, irrespective of the tree or nest type (i.e. vultures or raptors). There was no difference in elephant impact type and severity between trees with nests and those without nests, although trees with nests were taller and had a lower probability of insect and fungus present. Hence accumulated elephant impact on older trees could render these trees as unusable in the long run because of increased arthropod and fungus attack over time. Bark-stripping was found to be the most prolific elephant impact type for trees used by either vultures or raptors. There was relatively lower elephant impact on trees used by vultures compared to those used by raptors. Vultures generally nest in the upper crown compared to raptors that prefer nesting lower in the tree canopy. Consequently, vultures may be more sensitive to die-back on smaller branches than raptors because they depend on the buoyancy of these smaller branches to construct their nests.
Large trees were found to die much slower than what nests were disappearing. Hence changes in nest survival cannot be attributed to changes in tree survival alone but indicate that other factors are at play and we need todetermine at what scale are these other factors influencing the nesting potential of vultures and raptors, be they climatic changes or changes in the survival rate of breeding pairs. On the bright side of the future nesting sites for these valuable large tree-nesting birds, our results show that there is a high regeneration or recruitment of nesting sites on which elephants had an overall negligible influence during the study period.