US Geological Survey


Date of this Version



Published in Ornithological Monographs (2010) No. 67, 24-34. DOI: 10.1525/om.2010.67.1.24.


Scientific debate over identification of taxa below the species level has persisted for centuries. This issue can be especially problematic for avian species, because dispersal is often orders of magnitude greater than in other vertebrates, leaving genetic differences among groups proportionately smaller. While the debate lingers, management decisions, often with millions of dollars and potential extinctions resting on the outcome, are regularly made by agencies tasked with maintaining lists of threatened and endangered taxa. With outdated taxonomic treatments and no formal policy or guidelines for defining species or subspecies, agencies have no authority to cite in determining limits to species or subspecies ranges. Lack of guidance from professional organizations regarding taxonomic criteria and lists does not benefit these species of concern. Here, we describe how subspecies designations are evaluated under the Endangered Species Act, tradeoffs between maintaining the biological species concept in avian taxonomy versus adopting a phylogenetic species approach, and why it is imperative for scientific organizations to maintain updated taxonomic treatments regardless of the species concept they use.