The American Ornithological Society’s (AOS) Checklist of North American Birds (Checklist) and its annual supplements provide a standardized taxonomy for North American birds for use by government agencies, scientists, conservation organizations, and anyone that is interested in birds. Taxonomy, the science of classifying organisms, provides the foundation for effective science and conservation management and is encountered by most people in the form of species lists.
The Checklist has a long relationship with the USGS Eastern Ecological Science Center (EESC) at Patuxent Research Refuge in Laurel, MD. For the last 30 years, a research scientist from EESC has served as chair of the Committee on Classification and Nomenclature (Committee), which produces the Checklist. EESC research scientist Richard C. Banks chaired the Committee from 1995 to 2007, with Terry Chesser taking over as chair in 2008.
Apart from their use by individual scientists at EESC and across the continent, the Checklist’s annual supplements are used to update the avian taxonomy and species lists of two long-term foundational USGS science programs, the North American Breeding Bird Survey and the Bird Banding Laboratory. The Checklist is also heavily used by EESC partners, most importantly by the Migratory Bird Office of the US Fish & Wildlife Service, who use the annual supplements to update 50 CFR 10.13, the list of species covered by the Migratory Bird Treaty Act.
Why does the Checklist change?
“We live in exciting times for research on the systematics and taxonomy of birds, mainly due to the availability of new types of information such as vocal and genetic data,” said current Committee chair Terry Chesser. “The Committee evaluates about 50 proposals per year for changes to the taxonomy of North American birds based on the most recent research. Many of these proposals involve changes to species limits, mainly species splits. This happens when a species previously treated as one species is proposed to actually consist of more than one species. A good example of this was the proposed split of Eastern Meadowlark a couple of years ago.” The Committee also considers proposals for species lumps, in which what was previously considered to be more than one species is proposed to be a single species. Other proposed changes involve higher level taxonomy: for example, species previously placed in a single genus are proposed to consist of two or more groups of unrelated species, and so are proposed to belong to more than one genus.
What were some recent changes to the Checklist?
This year’s supplement to the Checklist, published earlier this summer, contained all change types mentioned above. Several species of seabird found in North American waters were split, including two species of shearwater (Cory’s Shearwater and Audubon’s Shearwater) found along the Atlantic and Gulf coasts, and Brown Booby, which nests in California and Hawaii and occurs elsewhere in the U.S. during the non-breeding season. All of these are listed on various state wildlife action plans as Species of Greatest Conservation Need. The familiar House Wren was split into no less than seven species, several of which are prevalent on single islands in the Caribbean, making them a prime conservation concern for the area. The Barn Owl that occurs in North and South America was recognized as a different species from barn owls in Europe, Africa, and Australasia.
Species lumps are unusual, but for the second consecutive year the supplement contained a species lump. Last year two species of Empidonax flycatcher, the Cordilleran Flycatcher and the Pacific Slope Flycatcher, were lumped into the single species the Western Flycatcher. This year two species of redpoll, the Common Redpoll and the Hoary Redpoll, were lumped into the single species the Redpoll.
At a higher level, the Committee adopted changes to the genus-level taxonomy of the bitterns and plovers. Bitterns have been placed traditionally into two genera, Ixobrychus for the smaller bitterns, such as Least Bittern, and Botaurus for the larger species, such as American Bittern. However, some species of the genus Ixobrychus were found to be more closely related to species of Botaurus than to other species of Ixobrychus, so the Committee now places all species in the single genus Botaurus.
In contrast, the Committee transferred some species of the typical plovers of North America, all of which were previously placed in the single genus Charadrius, into a separate genus. The group of plovers that includes Wilson’s Plover, Collared Plover, Mountain Plover, and Snowy Plover, have been transferred to Anarhynchus. Despite similarities in plumage and morphology to a second group of species that have been retained in Charadrius, including Killdeer, Semipalmated Plover, and Piping Plover, the Anarhynchus plovers have been shown to be more closely related to lapwings than to true Charadrius plovers.
What about changes that weren’t made?
Perhaps of equal importance to the changes that the Committee adopts are those that are considered but not adopted due to insufficient evidence in favor of a change. Many proposed species splits are not accepted because the Committee considered that the data do not support more than one species or because, although some data seem to support more than one species, other key data are currently lacking. In the most recent supplement, a proposal to split the Red-shouldered Hawk into eastern and western species was not accepted, although there was some support for the split and further data may tip the balance toward splitting this species.
What changes might be expected in the future?
The Committee’s work is ongoing and new proposals are continually being considered. Proposals expected for the upcoming year include a proposal to split the Warbling Vireo into eastern and western species, a proposal to lump Black-crested Titmouse into Tufted Titmouse, and a proposal to recognize the Great Egret of the Americas as a separate species from the Great Egret of the Old World. The Committee is also awaiting publication of new data on Steller’s Jay, White-breasted Nuthatch, Fox Sparrow, and Savannah Sparrow before considering splits of these species in the future. Keep up with the current list at https://checklist.americanornithology.org/taxa.
This United States Geological Survey news article "EESC Scientist Leads Committee Tasked with Classifying North American Bird Species" was originally found on https://www.usgs.gov/news
