Are the implications for conservation of a major taxonomic revision of the world’s birds’ simply serendipity?

Abstract

Taxonomic inflation—the increase in species richness through taxonomic rearrangement rather than species discovery—is a challenge to conservation (Isaac et al., 2004). The examination of the conservation impacts of taxonomic inflation on a group as large and diverse as birds is clearly a monumental task. Birdlife International’s recent revision increased the number of recognized bird species by some 10%, thus providing an opportunity to test whether taxonomic revision disrupts conservation. Simkins et al. (2020) conclude, with some surprise, that there was little impact on the number of species meeting IUCN’s international Red List criteria. They then extol the ‘clear benefits of improving understanding’ as outweighing what they describe as the ‘cost in terms of higher extinction risk, a reduction in the performance of site-based networks in capturing species’ ranges or a significant increase in the number of areas of high conservation threat that require a response’. Three questions arise from their analysis, which shows that the absolute number of globally threatened species increased only slightly overall, with no change in average extinction risk, and only one new place, eastern Amazonia, emerging as a global hotspot for threatened bird species (Simkins et al., 2020). First, while Simkins et al. (2020) describe the patterns that emerge, they do not explain why the result obtained was counter-intuitive, i.e. why it was that most of the split taxa failed to exceed the thresholds of the IUCN Red List criteria when split. Or why it was that many of those that did cross those thresholds, and thus warrant listing, were already encompassed within the Important Bird Area network. However, perhaps the results are not surprising after all. First, splitting mostly occurred in common species in which morphological discontinuities and regional dialects had not previously been acknowledged as meeting species criteria. Such common species are probably not rapidly declining so, even if the ranges of split taxa cross the area or population size Red List Criteria, they cannot be listed as threatened unless they are also declining sufficiently to meet the Red List Criteria or there are fewer than 1,000 mature individuals. Secondly, the few species that do cross listing thresholds when split are probably more likely to occur in landscapes where more obvious splits had already been recognized. These are the species used to characterize the IBAs (Important Bird and Biodiversity Areas) that the newly split species now join. It is also possible that the result is serendipitous. Simkins et al. (2020) admit they do not know how their findings might apply to other groups of organisms. They also do not know if they would get the same results with different settings of the taxonomic criteria applied. The Tobias revision (Tobias et al., 2010) is unusually specific in setting criteria for what constitutes a species or not, allowing hypotheses to be tested in a manner not available to other forms of species delineation. Theoretically it should then be possible to set a higher or lower bar for what constitutes a species and explore the ‘species’ patterns that emerge. A lower threshold might mean many more species and many more gaps to fill in the IBA network. Alternatively, a higher threshold of difference could lead to widespread lumping of similar forms and the newly emerged hotspots for IBA investment would sink into a sea of taxonomic homogeneity. Which exposes a third facet of the analysis: the thresholds for the Tobias criteria (Tobias et al., 2010) were determined primarily by scientists in the global north. In fact, nearly all expressions of taxonomic freedom are exercised in the global north. Many taxonomists have strong ties to conservation, creating an apparent conflict of interest even if the taxonomists concerned are impeccable at separating their aspirations for conservation from their decisions about taxonomy. It is nevertheless telling that Simkins et al. (2020) have to point out that the benefits of improving our understanding of taxonomic units are “clear” compared to the theoretical “cost of higher extinction risk”. Quite apart from their incommensurability, while the gains are to one sector of global society, the costs are often to another. The areas that emerged requiring increased protection were in the global south—eastern Amazonia, Java and the Philippines—all of them areas where Indigenous Peoples have rights to much of the land (Garnett et al., 2018) but are commonly disempowered by the State. Personally we might advocate increased protection for these areas, and might see the advantages of retaining as much of the diversity of these areas as possible and grieve for the losses likely to occur. However, people eking out livelihoods in those areas who might be affected by protecting habitat that they need to feed their children had no say in what was transparently a subjective process of setting taxonomic thresholds. That the same people could eventually benefit from appropriate conservation investment (see Waldron et al., 2020) does not detract from the argument that the subjective parts of taxonomy, as opposed to the technical aspects (Zachos et al., 2019), are inherently political with real-world consequences. Each of the four global lists of birds mentioned by Simkins et al. (2020) is likely to produce different spatial patterns of cost and benefit. Each would claim some form of legitimacy derived from the sectors they serve and the uses to which they are put. Although the differences between these lists may be minor when directly compared, it is their usage that leads to more profound issues. When these differences are followed by others in the peer-reviewed literature, the effects compound. What any of the four lists currently lack, however, is any formal endorsement as the list best suited to everyone. This may change given an expressed desire to create a single global bird list (Collar, 2018; McClure et al., 2020) and principles (Garnett et al., 2020) on how a single taxonomic list could deliver the institutional legitimacy to the taxonomic revisions of the sort described by Simkins et al. (2020). This shifts the argument from whether global taxonomic revisions hinder or hamper conservation to whether the revisions have been endorsed by global science before their application to the real world. Endorsed taxonomic lists would no longer need to justify themselves. Rather the users of taxonomy could get on with dealing with the consequences of taxonomic decisions, confident that the entities with which they aim to engage are endorsed by the strongest governance structure global science can provide.