Birder's Guide

OCT 2014

Birder's Guide is the American Birding Association's newest publication. Each issue focuses on a key subject, providing tips from experienced birders on a wide variety of topics like Travel, Listing & Taxonomy, Gear, and Conservation & Community.

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Page 25 of 57

24 Birder's Guide to Listing and Taxonomy | October 2014 Species & Subspecies : A Brief History headache they pose. Crossbills are prob- ably now the superstars of sympatric speciation in birds (Smith and Benkman 2007). There are at least 10 described call types in North America. Each call type cor- responds to a population that seems to feed on certain types of conifers. These popula- tions show only limited segregation by ge- ography and imperfectly known degrees of reproductive isolation (Benkman et al. 2009; Irwin 2010; Groth 1993). While crossbills have achieved the most atten- tion, with even a recent proposal to elevate the "South Hills Crossbill" to species status (Benkman et al. 2009), call note differenc- es have been noted in other related fnches (Sewall et al. 2004; Adkisson 1981). Might there be more cryptic sympatrically-evolv- ing populations amongst Evening and Pine grosbeaks? Future research will tell. These are just a few of the current hot- button issues in bird speciation and tax- onomy. No doubt, more will appear over time, and these will infuence how species concepts are interpreted and applied. The science behind taxonomy, much like the birds we so enjoy watching, is a constantly evolving feld. Thanks to Richard Klim for helpful comments that improved this manuscript. Glossary Allopatric Speciation. Speciation that re- sults from populations being in allopa- level, and until then subspecies may con- tinue to be dubious taxonomic units. Future Challenges One problem I foresee for future taxonomic committees is dealing with cryptic species, exemplifed by many of the storm-petrels. For instance, Band-rumped Storm-Petrel is now known to represent several popula- tions which segregate for breeding by is- land and time of year (Friesen et al. 2007; Monteiro and Furness 1998). Increasing evidence supports these forms as being reproductively isolated species, but there are few morphological differences between populations. Almost certainly this phe- nomenon exists in other pelagic seabirds, and possibly other bird groups. Hybrid speciation is a major factor in plant evolution (Soltis and Soltis 2009), but until recently has not been strongly advocated in birds. Though still rare, there is evidence that hybrid speciation in birds might be more important than previously considered, though, and may have played a role in the evolution of "Audubon's" Yellow-rumped Warbler (Brelsford et al. 2011), Italian Sparrow (Hermansen et al. 2011), and Pomarine Jaeger (Blechschmidt et al. 1993). Hybridization has the poten- tial to seriously bias phylogenetic analyses, and the taxonomic status of some of the above species is still debated. By now, most birders have heard about crossbills and the potential taxonomic jor factor in the splits of Northern Oriole and Yellow Wagtail. Reproductive isola- tion remains a major component of how the AOU's North American Classifcation Committee (NACC) makes its decisions, but aspects derived from other species concepts have slipped in. Study of bird vocalizations using sonograms and use of statistics in looking at differences in shape and plumage in birds has also resulted in taxonomic change. Unless they are rumored to be full spe- cies in disguise, subspecies are still largely neglected by researchers, and the last edi- tion of the AOU Check-list to reevaluate them was published in 1957. However, Remsen (2010) has recently advocated treating phylogenetic species as subspecies under the BSC. This proposal would nice- ly accommodate subspecies as units for evolutionary analysis, and would trans- late the "75% rule" to diagnosis of species under the PSC. If this concept could be widely implemented, it would mean that bird checklists could include both species concepts in their application. I suspect, though, that it will take decades of taxo- nomic research before we can thoroughly evaluate North American (let alone world- wide) bird populations at the subspecifc These two Song Sparrows exhibit profound clinal variation. The large, long-billed, cold-colored, dark, coast- al-dwelling Alaskan bird and the small, short-billed, warm-colored, pale, desert-dwelling Arizona bird are well suited to their local climates and habitats. Photos (left to right) © Jim Zipp, Brian E. Small

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