The two Buphagus oxpecker species are specialized passerines that forage for ticks and other food particles on the body of ungulates in the African savannas. One of their intriguing features is their ability to coexist despite sharing the same, specialized diet. Using co-occurrence data (photographs of giraffes with oxpeckers on them) and Approximate Bayesian Computing, we demonstrate that yellow-billed oxpeckers changed host faster than red-billed oxpeckers and appeared to displace red-billed oxpeckers from preferred giraffe body parts. Conversely, red-billed oxpeckers exhibited a fuller use of each host and displaced yellow-billed oxpeckers from distal giraffe body parts. These findings highlight that the partition of giraffe hosts in two separate niches was only part of the coexistence story in this species pair. More precisely, the oxpeckers shared resource by exploiting it at different rates. They engaged in different trade-offs between giving-up density, patch discovery rate, and competitor displacement ability. They illustrate the importance of the time frame of interactions.

Observers opportunistically photographed giraffes between 2007 and 2015 during the day from the network of tracks in the woodlands of the northeast of Hwange National Park, Zimbabwe (19°00’S, 26°30’E). We retained 345 pictures featuring the full left or right side of giraffes with oxpecker on them (42% had no oxpecker). RG marked down the oxpeckers with an estimated 99% detection rate (double observer protocol; Gagnon et al. 2019). GP identified the oxpeckers to species with an estimated rate of misidentification <2% (after a two-step process; Supplementary Material S1). We only used pictures in which GP assessed that any bird in full view could have been identified given the distance and resolution of the photograph, thereby avoiding a bias towards adult oxpeckers and towards pictures with fewer identification challenges. The final sample size was 134 individual giraffes photographed between 9am and 5pm. Lastly, we located the oxpeckers on the bodies of the giraffes (abdomen, ano-genital area, back, rump, groin, head, lower leg, mane, neck, scapula, shoulder, tail, thigh, or upper leg; see Gagnon et al. 2019 for full detail).

RO = number of red-billed oxpeckers

YO = number of yellow-billed oxpeckers