Habitat selection by an extraordinary savannah raptor: environmental factors driving abundance of the Secretarybird Sagittarius serpentarius in the Serengeti National Park (Tanzania)

Capsule: We estimated the population size of the Secretarybird in the Serengeti National Park and identified ecological factors characterizing the high-density areas, which should be established as high-priority conservation zones. Aims: To estimate the abundance and density of Secretarybird within the Serengeti National Park (SNP) and investigate environmental variables driving its abundance. Methods: In 2023, Secretarybirds were counted along 52 transects (average length = 15.3 ± 1.8 km), replicated at least three times outside of the breeding season. Twelve transects with the most observations were repeated up to eight times. Abundance and density were estimated through multiple-covariate distance sampling, while habitat selection was assessed using generalized additive mixed models and generalized linear models. Results: We estimated an average density of 1.3 Secretarybirds/10 km2 and an abundance of 1,513.3 individuals. Areas of highest density averaged 2.3 Secretarybirds/10 km2 and 622.5 individuals. The greatest abundances occurred in transition zones between extensive grassland with high vegetation cover and habitats characterized by open woodlands or treed shrublands. Secretarybirds preferred flat environments with relatively more seasonal rivers and an annual precipitation of < 900 mm. Abundance decreased in grasslands with low vegetation cover and where open grassed woodland coverage was >20%. The probability of spotting single individuals versus pairs was higher in the western and central SNP and in more heterogeneous habitats with greater coverage of open grassed woodland and dense treed grassland. Closed treed shrublands were preferred by pairs. Secretarybird abundance was lower where the proportion of habitat burned for prescribed fires exceeded 60%. Conclusion: These results for the Secretarybird’s demography and ecology in the Serengeti ecosystem are essential for a long-term monitoring programme and conservation actions in Tanzania.