1. Dietary studies in birds of prey involve direct observation and
examination of food remains at resting and nesting sites. Although these
methods accurately identify diet in raptors, they are time-consuming,
resource-intensive, and associated with biases from the feeding ecology
of raptors like Gyps vultures. Our study set out to estimate diet
composition in Gyps vultures informed by stable isotopes that provide a
good representation of assimilated diet from local systems.2. We hypothesized that differences in Gyps vulture diet composition is
a function of sampling location, and that these vultures move between
Serengeti National Park and Selous Game Reserve protected areas to
forage. We also, theorised that grazing ungulates are the principal
items in Gyps vulture diet.3. Through combined linear and Bayesian modelling, diet-derived from
13C in Gyps vultures consisted of grazing herbivores across sites, with
those in Serengeti National Park consuming higher proportions of grazing
herbivores (> 87%). 13C differences in vulture feather
subsets did not indicate shifts in vulture diet and combined with blood
13C, vultures fed largely on grazers for ~159 days
before they were sampled. Similarly, 15N values indicated Gyps vultures
fed largely on herbivores. 34S ratios separated where vultures fed when
the two sites were compared. 34S variation in vultures across sites
resulted from baseline differences in plant 34S values, though it is
not possible to match 34S to specific locations.4. Our findings highlight the relevance of repeated sampling that
considers tissues with varying isotopic turnover and emerging Bayesian
techniques for dietary studies using stable isotopes. Findings also
suggested limited vulture movement between the two local systems.
However, more sampling coupled with telemetry is required to fully
comprehend this observation and its implications to Gyps vulture ecology
and conservation.