"Wisdom begins with putting the right name on a thing"
(Old Chinese Proverb)

Classification

The  original version of the IOC World List (Gill and Wright 2006) mostly followed  the classification and sequence of families in the third edition of the Howard and Moore Complete Checklist of the  Birds of the World (Dickinson 2003). That classification reflected the  phylogenies based on DNA data available at that time, summarized in the chapter  on “Avian Higher-Level Phylogenetics” by Cracraft,  Barker, and Cibois.

DNA sequences clarify (or erase) some of the connections between the  deepest historical branches of avian evolution (Hackett et al 2008). Accordingly,  we can revisit the compositions of the classical Orders of birds and the relationships  among them.  Some groups (clades) of bird  species are not as closely related to each other as previously thought. DNA-based  resolutions of the phylogenetic relationships among world birds have increased  dramatically in the past few years, and will continue to multiply.  Many of the latest results are available on  the web as part of the Tree of  Life (TOL) project. Other  excellent resources include John Boyd’s website Taxonomy in Flux .

We  now have the ability to to distinguish taxa of similar rank that are reciprocally  monophyletic. This lets us redefine some groups of species that in hindsight  were paraphyletic. Changes in taxonomy follow, especially splitting of orders,  families, and genera to define monophyletic taxa that can be reconnected to  their closest relatives in the classification. Genera also change with corrections of nomenclature and the rules of priority. As a result, we can expect increasing instability of working classifications for a decade or so.  Continually improving sets of DNA sequences and analytical approaches also may override previous conclusions, so cautious revisions of higher category taxonomy and new sequences of taxa seem prudent.

Our  policy, therefore,  is to change higher level classification and sequences of taxa conservatively.  Stability is important, and being creatures of habit we all find a particular taxon or species  more easily in a familiar sequence, even if dated.

UPDATES OF IOC CLASSIFICATION (3.1)   TO DO