Cothreatened hosts and parasites causes range contraction of an avian mutualist

Riddhika Kalle (1), Leigh Combrink (1,2) , T. Ramesh (1), Colleen T. Downs (3)

1 School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville, Pietermaritzburg, KwaZulu-Natal, 3209, South Africa,

2 The Endangered Wildlife Trust, South Africa

Distributions of birds are affected by changes in host-parasite densities and environmental conditions driven directly or indirectly by human actions. We predicted the distribution of an avian mutualist, the red- billed oxpecker Buphagus erythrorhynchus by incorporating biotic interactions (trophic relationships, host- parasite relationships, hetersopecific interactions) through niche models at macroecological scales. We used biotic variables, climate, vegetation, topography, water and proximity to protected areas to predict occurrence and evaluated the predictive performance of models using three modelling techniques (generalised linear models, generalised additive models, boosted regression trees) and ensemble models. Abiotic–biotic models described the current range of red-billed oxpecker in South Africa and outperformed other models. The most influential predictors were tree cover, bioclimate, domestic and wild host density, tick density, topography, distance to protected areas and occurrence of starlings. Our models showed that the current range of red-billed oxpeckers has contracted, covering only 12,796.23-15,185 km2  of suitable habitat (≥0.5). The Limpopo and the northern KwaZulu-Natal provinces were the major strongholds of suitability in South Africa. Few suitable areas in the North West province can be linked to the increasing artificial woodlands. Our study highlighted the need to involve biotic interactions within co-dependent species and its interactions with climate as key limiting factors when modelling the distribution of wildlife species to make ecologically realistic predictions at macro-scales. Conservation interventions through active reintroductions  of  these birds in suitable habitats identified in our predicted maps, and the use of oxpecker-compatible agrochemicals may aid in the population recovery of red-billed oxpecker in certain areas.