Calculations of undetected untagged rhino that avoided us

2020-04-10T06:55:31Z (GMT) by Roan Plotz
To study the role that oxpeckers might play in helping rhino evade humans, we recorded the number of oxpeckers seen on two groups of the rhinos we encountered. Rhinos tagged with radio transmitters- which allowed us to track them using radiotelemetry while evading detection from oxpeckers- carried the bird on their backs more than half the time (56%). The untagged black rhinos we found, carried no oxpeckers most of the time (17%). Our data suggests that other untagged rhinos which carried the birds might have avoided encountering the us altogether. Using the difference we observed between oxpeckers on the tagged versus untagged rhino, we estimated that between forty to fifty percent of all possible black rhino encounters were thwarted by the presence of oxpeckers. Therefore, we used the average oxpecker number on tagged rhino as a baseline estimate for average oxpecker presence on the wider rhino population. We then used the difference in oxpecker number seen on tagged and untagged rhino to estimate the proportion and number of potential untagged rhino encounters that were prevented by resident oxpecker on rhino, given hypothetical numbers of occasions that rhino evaded us (Ru) during our activities in the study area to generate 100 rhino encounters (Rd: such that Ru + Rd = the total number of encounters possible). Data used to develop Figure 1, also see Quantification and Statistical analysis in STAR methods to see Equation 1 and how the number of untagged rhino with oxpecker that avoided us were generated. As expected, the % Ruo asymptotes towards 56% (the proportion of oxpecker present on rhino with horn implant transmitters) where Ru is large, i.e., ≥400, because 20% or fewer of all rhino, i.e., (Ru/ (Rd + Ru)) × 100 = 100/500, are assumed to have been detected.

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