“…By comparing this grouping to previously published chemical analyses of penguin droppings, the authors confirmed that the group of bio-elements is representative of the species of interest, and so could be used to understand changes in penguin numbers back in time. R-cluster analysis, which has been used worldwide, is often considered the most effective tool to identify ornithogenic elements if a nearby reference site (i.e., a nearby lake without avian inputs) is not available to distinguish the natural, background element concentrations (Zale, 1994;Sun et al, 2000Sun et al, , 2004Liu et al, 2005Liu et al, , 2006cHuang et al, 2009aHuang et al, , 2011Xu et al, 2011Xu et al, , 2016Xu et al, , 2019Xu et al, , 2020Roberts et al, 2017).…”