"Costs" and Short-Term Survivorship of Hornless Black Rhinos

The devastation of Africa's black rhinos (Diceros bicornis) by poaching (Western 1987) highlights the challenges found at the interface of biology and economics (Leader-Williams & Albon 1988). One of the most controversial conservation actions to date has been the removal of horns from black and white rhinos. Here we explore economic and biological implications of horn removal using data gathered in Namibia in 1991, 1992, and 1993. Specifically, we make three points. First, horn regrowth is rapid, averaging nearly 9 cm of total horn per animal per year, a finding that suggests new horns on an average animal are worth $1775-7750 one year after dehorning. Second, because poachers fail to discriminate between large- and small-horned rhinos, recently-dehorned animals may not be immune from poaching. However, neither horned nor hornless rhinos differed in their vulnerability to poachers more than four years after the initial dehorning. Third, for mothers that varied naturally in horn length, calf age and not horn size affected responsiveness to dangerous predators such as lions (Panthera leo) and spotted hyenas (Crocuta crocuta).