Vulture – Tree Links

South Africa’s white backed vulture is now Critically Endangered, and its 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.

Other large raptors, as well as Southern Ground Hornbills are also decreasing due to loss of habitat, bush-encroachment, overgrazing and plantations, loss of nesting trees, secondary poisoning and electrocution.

Both vultures, raptors and Southern Ground Hornbills depend on large trees for nesting. Their breeding success can therefore be influenced by elephants impacting the trees used by these bird species as nesting sites. 

Therefore, since 2008, Elephants Alive has been monitoring, on an annual basis, 62 large trees used by southern ground hornbills as nesting sites, and 226 trees used by raptors and white backed vultures as nesting sites to understand the influence of elephant impact on these sites.

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 to determine 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.