In February, the second chapter of my PhD was published in Ecological Indicators. This paper looks at how sensitive our understanding of global bird trends is to how we classify bird groups.
It’s common practice to use composite indices to try and understand global biodiversity trends. The European Bird Census Council is just one institution that does this, calculating an index of temporal trends in farmland and forest bird species. These bird groups (farmland and forest/woodland) are studied by many researchers and institutions, though in each case different combinations of species are assigned to the different groups.
In this paper I looked at how sensitive the trends in composite bird indices of farmland, forest/woodland and generalist birds are to which species are included in each group. We find that the trends we calculate in these bird groups can change drastically depending on which species are included (using actual, published lists of species assigned to these groups). In some cases, this effect is severe enough that under some definitions a positive trend is seen and under others the trend appears to be negative.
Our results question the current practice of idiosyncratically classifying indicators in scientific research and conservation. This inconsistency is making it more difficult to infer whether and when to preserve bird groups, potentially leading to sub-optimal conservation outcomes.