Avian Higher-level Phylogenetics and the Howard and Moore Checklist of Birds by

As phylogenetic knowledge has increased over the past 40 years following the introduction of cladistic theory and methodology, systematists have increasingly attempted to make classifications reflect phylogenetic relationships. Given an hypothesis of relationships it is reasonably straight-forward to express those relationships within the context of hierarchical classifications in a number of different ways. Ornithologists have addressed this issue for over 20 years (e.g., Cracraft 1981) (2999)1 . Without question the best-known attempt at constructing a phylogenetic classification for avian higher taxa was that derived from DNA hybridization distances (Sibley et al. 1988; Sibley & Ahlquist 1990; Sibley & Monroe 1990) (3025, 2610, 2030). However there are many other examples at lower hierarchical levels within birds (e.g., Livezey’s 1998 classification for gruiforms) (3017). The present volume — a list of avian species — does not arrange these within a series of hierarchies but instead uses, aside from the Linnean binomial of genus and species, two hierarchical levels, the family and the subfamily. Because knowledge of avian phylogenetic relationships is still clouded with uncertainties, any decision to recognize a complex classificatory hierarchy would have resulted in numerous arbitrary choices. We have attempted to reflect currently accepted hypotheses of relationships to the extent possible within a linear sequence. We have followed a simple set of conventions. First, the list sequentially clusters families in a way that represents what are thought to be groupings of related families; many of these follow traditional orders when compelling alternative evidence is not available. Second, within each of these clusters, subgroups of related families are listed near one another. Finally, within all such groups and subgroups, the presumed basal families are listed first. This volume is not the place to present an extended discussion about the higher-level relationships of birds. Nevertheless, the present list attempts to incorporate recent evidence on relationships, with the caveat that often the best evidence presently available is only of a single kind — for example, either morphology or molecular. Ideally we would like to have congruence across data sets before concluding that a satisfactory understanding of those relationships has been attained. This is a time of unprecedented activity in avian systematics, with more investigators collecting data than at any time in history. Consequently, understanding of avian relationships is changing rapidly. In discussing the evidence, only that work which is published, or in press, is mentioned. The list errs on the side of conservatism because a list of species, designed in part for a popular audience, is not an appropriate venue for making radical changes. Over the years, and continuing to the present, there have been many calls to dismember traditional orders, but most of these opinions are based on evidence that is still not widely accepted within the systematic community, where ideas about relationships remain contentious. In the following remarks, not all groupings (orders) will be discussed, either because there is relatively little dispute over relationships or because there has been no new information about relationships published in recent years.