Birder's Guide

OCT 2017

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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Birder's Guide to Listing & Taxonomy | October 2017 36 his year, the topics most likely to generate discussion are splits of Red Crossbill and Magnificent Hummingbird, a lump of Thayer's and Iceland gulls, and a resolution of sorts into the taxonomic affiliations of the unique Yellow-breasted Chat. There are also many changes that affect species found only in the Caribbean or south of the U.S.–Mexico border. They are detailed on the ABA Blog at tinyurl.com/ AOU2017. Hello to the Cassia Crossbill –––––––––––––––––––––––––––––––––– • Red Crossbill (Loxia curvirostra) • Cassia Crossbill (Loxia sinesciuris) In the Albion Mountains and South Hills of Cassia County, Idaho, there are no tree squirrels. Scientists have convincingly argued that this novel situation has al- Check-list Supplement Redux, v. 2017 T Every summer, birders anxiously await publication of the "Check-list Supplement" by the American Ornithological Society's Committee on Classification and Nomenclature of North and Middle American Birds (a.k.a. the NACC). The supplement details revisions to the NACC's Check-list. This "Check-list Redux", the seventh annual summary appearing in ABA publications, aims to explain in straightforward terms what has changed and how those changes impact anyone birding in the U.S. or Canada. Illustrations, photos, charts, and maps are employed where applicable. You can read all the proposals on which the NACC voted this year at checklist.aou.org. Species marked with asterisks (*) below are those which do not appear on the ABA Checklist, either because there are no currently accepted records in the ABA Area or because they are non- natives that have not yet been admitted to the list. Daggers (†) denote extinct species. Nowadays, it can be assumed that any change in taxonomy is due (at least partly) to analysis of new genetic data, so that is not always mentioned below. As a general policy, the NACC accepts as additions to its North American Check-list any species the ABA's Checklist Committee adds to its list. Those changes are not listed here. lowed for the evolution of the area's very own resident species of crossbill: Loxia sinesciuris, known as the Cassia Crossbill. Indeed, sinesciuris means "without squir- rels". In most of the Rockies, the seeds of lodgepole pine (Pinus contorta) are eaten, stored, and buried by tree squirrels such as the red squirrel (Tamiasciurus hudsoni- cus). In Cassia County, however, there are no squirrels, so the pines have been locked in an evolutionary arms race with but one main predator: the crossbill. Over thou- sands of years, the pine evolved bigger and harder cones to prevent the crossbill from accessing its seeds. And the crossbill evolved a bigger, deeper bill and stronger facial muscles in order to pull the seeds out of the cones. This situation is remarkable because it happened in the presence of other cross- bills. Two "types" of Red Crossbill (2 and 5), from which Cassia Crossbill was split, still commonly visit the area. But cross- bill flocks are very cohesive and seem to form regional dialects quickly. The Cassia Crossbill not only has a different bill struc- ture compared to the Red Crossbills with Cassia Crossbills, such as this adult male, are essentially visually identical to Red Crossbills in the field. Photo © Craig Benkman Range of Cassia Crossbill. Map © Rad Smith

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