Impacts of African elephants and other environmental drivers on trees nested in by critically endangered white-backed vultures

The decline of white-backed vultures (Gyps africanus, hereafter termed
vultures) across Africa highlights the need to understand their
habitat and nesting requirements, especially in protected areas
where African elephants (Loxodonta africana) can impact the trees in which
vultures build their nests. Our study aimed to assess the impact
that elephants have on trees containing vulture nests in the
Associated Private Nature Reserves (APNR) of South Africa’s savanna
system through three separate but interlinked assessments. We
first assessed the tree species used by vultures for nesting and
compared their size and elephant impact scores between riparian
and woodland habitats. We assessed how elephant presence or
absence affects the size of Senegalia nigrescens, a key tree
species, and compared vulture nests in an adjacent elephant-free
area. Lastly, we modeled environmental factors influencing
vulture nest and tree persistence using data from 2008-2020.
Vultures utilised 10 tree species, with riparian trees supporting nests
being significantly taller, with larger DBHs, and experienced
lower elephant impact compared to woodland trees, which were more
heavily impacted by elephants. Less robust species like
S. nigrescens were more vulnerable to elephant damage, primarily
bark-stripping, and less likely to host vulture nests. Our
results show that vultures prefer the largest, least impacted trees
for nesting, favouring those with greater stability and
longevity. We suggest that although elephants influence the
overall height range of trees to vultures, strong gusts of wind have a
strong negative contribution on vulture nest persistence and that
only a relatively small number of trees died during the 12-year
study in comparison to fallen nests. We recommend further research
into elephant impact thresholds on trees and vulture nest
selection. Monitoring treefall and regeneration rates will help
predict when vultures may face a shortage of suitable nesting trees.