Response to ‘Risky conclusions regarding shrinking rhino horns’: Clarification on a statistically determined reduction of relative horn length in five species of rhinoceros since 1885

In their response to Wilson, Pashkevich, Rookmaaker, et al. (2022), Ferreira et al. argue that our conclusions regarding shrinking rhino horns were risky, given the low sample size used for this assessment, the variation in rhino horn length related to non‐heritable factors (including age, sex, environment and behaviour) and the low impact that current selective trophy hunting has on rhino numbers. We agree that our sample size was low and that many factors can influence horn length and therefore we discussed these points as important caveats in Wilson, Pashkevich, Rookmaaker, et al. (2022). However, we argue that although many factors can lead to variation in horn length, they do not explain the decline in relative horn length over time that we observed, and we note that the response does not offer an alternative explanation for this temporal shift. Although selective hunting is currently a minor factor in rhino mortality, this may have been relatively more important and to have had a potentially greater selective influence in the past. Our dataset does not allow identification of factors driving this change, and in Wilson, Pashkevich, Rookmaaker, et al. (2022), we offered selective hunting as one possible explanation for the relative decline, calling for more work to investigate this further. We highlight that the focus of Wilson, Pashkevich, Rookmaaker, et al. (2022) was far more than an assessment of changing relative horn length and instead aimed to demonstrate that a wide range of data can be extracted effectively from image repositories for use in a conservation context. We hope that the results in Wilson, Pashkevich, Rookmaaker, et al. (2022) will provide a useful starting point for future research, including addressing the questions raised by Ferreira et al. Ultimately, we feel that the attention given to Wilson, Pashkevich, Rookmaaker, et al. (2022) reveals the enduring interest people have in rhinos, a topic addressed in other parts of our original paper, which we encourage readers to read in its entirety. Read the free Plain Language Summary for this article on the Journal blog.