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24 Birder's Guide to Listing & Taxonomy | October 2016 Species Changes mingbird has not been recorded here), it is not included in the table. A list of potential splits and lumps involving extralimital spe- cies is provided online in Appendix 1. In some cases, not all members of a po- tential split or lump are of equal standing. For example, Ipswich Sparrow (ssp. prin- ceps) is usually recommended to remain within Savannah Sparrow (Passerculus sandwichensis). Some birders may be sur- prised to not see a potential lump of Blue- winged Warbler (Vermivora cyanoptera) and Golden-winged Warbler (V. chrysop- ter) or a re-lumping of the Yellow-bellied Sapsucker complex. Current evidence, such as it exists, supports these longstand- ing decisions, and there have been no seri- ous challenges to the status quo. Common names used in Table 2 are either in current usage for the species groups or descriptive when no common name is available. The use of these names should not be considered an endorsement for one name over another. The key to Table 2 presents a list of char- acteristics (similar to those provided in Tobias et al., 2010) for which each poten- tial split and lump is coded as to whether there is evidence available (usually pub- lished) to support or refute the change in taxonomy. The most common characteris- tics used are differences in vocalizations, plumage and soft part color and pattern, and morphology (size and structure). But other characteristics can be informa- one time, the interbreeding of two forms across a contact zone with viable interme- diate individuals was a sufficient criterion for treatment as one species. Looking back to the sixth edition of the AOU Check-list (1983), many species pairs fit into this sce- nario. Baltimore and Bullock's orioles, all of the rosy-finches, and Myrtle and Audu- bon's warblers were lumped into single species (Northern Oriole, Rosy Finch, and Yellow-rumped Warbler, respectively). But now a hybrid zone that is character- ized as narrow and stable is viewed as evi- dence for lack of free interbreeding. Often, the fitness of hybrids is seen as being vi- able only within a narrow geographic zone due to particular climatic or habitat con- ditions. As a result, several of these pairs have been re-split as separate species, with the split typically supported by evidence for divergent vocalizations and genetics. Hybrid zones characterized as being wide and geographically unstable (either moving in one direction or another or not tied to a particular climatic or habitat zone) are often interpreted as evidence for single species status. Northern Flicker is a good example of such a species, with the ex - tremes in the ABA Area (Yellow-shafted and Red-shafted) connected by a wide, unstable integration zone (Wiebe and Moore, 2008). Potential Splits and Lumps in the ABA Area Table 2 (starting on p. 28) presents a com- prehensive list of potential splits and lumps in the ABA Area that result in a net gain or loss of species. The included species groups are often well represented and dis- cussed in the literature, but there are a few based on more anecdotal information that are included for completeness. All of these species pairs or groups are more "gray" in terms of allopatry and hybridization, which is why their current taxonomy has been the subject of ongoing question and research. Not included are species changes that result from a different treatment with ex - tralimital groups. For instance, Magnificent Hummingbird may be split, resulting in the more northerly Magnificent Hummingbird (Eugenes fulgens sensu stricto) and the Costa Rican/Panamanian Admirable Humming- bird (E. spectabilis) (Zamudio-Beltrán and Hernández-Baños, 2015). Because this split would not result in a net increase in total species in the ABA Area (Admirable Hum- n "Western" Warbling Vireo. Photo © Bob Steele n "Coppery-tailed" Elegant Trogon. Photo © Greg Lavaty n "Atlantic" Northern Fulmar. Photo © Keith Barnes