DNA Reveals Possible Bird List Changes

Genetic barcoding of North American bird species suggests that fifteen current species may need to be split into two or more species, while forty-two current species may actually represent seventeen species. The barcoding of North American birds was done in support of a project to create a database of the DNA of all living creatures. So far, 643 out of 690 North American breeding species have been analyzed.

The project analyzed a small strand of mitochondrial DNA from each species sampled and compared the results against current taxonomy lists. It found that the vast majority (94%) of recognized bird species in North America correspond closely with distinct genetic clusters. Four percent are closely-related species represented by a single distinct cluster. Two percent of current species show two distinct clusters, suggesting the need for a split. (An academic paper describing the genetic barcoding project is available for free. The article describing the avian research is published in Molecular Ecology Notes, Comprehensive DNA barcode coverage of North American birds. If you cannot access the bird paper via the Blackwell link, try this pdf link. The project's website is here.)

Splits

In birding terminology, dividing a species into two or more is called a split and combining two or more species into one is called a lump. Species with a genetic variation over 2.5% were recommended for splits. The differences ranged from 3.1% in Northern Fulmar and Western Screech Owl to 7.9% in Marsh Wren. Potential splits are listed below. The genetic variation cited by the article corresponds to recognized subspecies with distinct geographic ranges. The Sibley Guide illustrates recognizable differences among different populations for most of these species. However, the differences are usually subtle, so field identification of new species will remain a challenge unless their range boundaries are clearly demarcated.

1	Northern fulmar	Fulmaris glacialis
2	Solitary sandpiper	Tringa solitaria
3	Western screech owl	Megascops kennicottii
4	Warbling vireo	Vireo gilvus
5	Mexican jay	Aphelocoma ultramarina
6	Western scrub-jay	Aphelocoma californica
7	Common raven	Corvus corax
8	Mountain chickadee	Poecile gambeli
9	Bushtit	Psaltriparus minimus
10	Winter wren	Troglodytes troglodytes
11	Marsh wren	Cistothorus palustris
12	Bewick's wren	Thyromanes bewickii
13	Hermit thrush	Catharus guttatus
14	Curve-billed thrasher	Toxostoma curvirostre
15	Eastern meadowlark	Sturnella magna

Lumps

The species that share close genetic characteristics are shown in the table below. Some of these are easily separable in the field, such as Black Duck vs. Mallard, the two teals, or the two eiders in breeding plumage. Others present real identification challenges, even though some individual species may be easily identifiable. Many birders may be relieved to see eight species of gulls lumped together, except for those who already have gone to the trouble of finding and identifying all of those species.

1	Snow goose	Chen caerulescens
	Ross's goose	Chen rossii
2	American Black duck	Anas rubripes
	Mallard	Anas platyrhynchos
	Mottled duck	Anas fulvigula
3	Blue-winged teal	Anas discors
	Cinnamon teal	Anas cyanoptera
4	King eider	Somateria spectabilis
	Common eider	Scomateria mollissima
5	Sharp-tailed grouse	Tympanuchus phasianellus
	Greater prairie-chicken	Tympanuchus cupido
	Lesser prairie-chicken	Tympanuchus pallidicinctus
6	Western grebe	Aechmophorus occidentalis
	Clark's grebe	Aechmophorus clarkii
7	Laughing gull	Larus atricilla
	Franklin's gull	Larus pipixcan
8	California gull	Larus californicus
	Herring gull	Larus argentatus
	Thayer's gull	Larus thayeri
	Iceland gull	Larus glaucoides
	Lesser black-backed gull	Larus fuscus
	Western gull	Larus occidentalis
	Glaucous-winged gull	Larus glaucescens
	Glaucous gull	Larus hyperboreus
9	Red-naped sapsucker	Sphyrapicus nuchalis
	Red-breasted sapsucker	Sphyrapicus ruber
10	Black-billed magpie	Pica hudsonia
	Yellow-billed magpie	Pica nuttalli
11	American crow	Corvus brachyrhynchos
	Northwestern crow	Corvus caurinus
12	Townsend's warbler	Dendroica townsendi
	Hermit warbler	Dendroica occidentalis
13	Golden-crowned sparrow	Zonotrichia leucophrys
	White-crowned sparrow	Zonotrichia atricapilla
14	Dark-eyed junco	Junco hyemalis
	Yellow-eyed junco	Junco phaeonotus
15	Snow bunting	Plectrophenax nivalis
	McKay's bunting	Plectrophenax hyperboreus
16	Great-tailed grackle	Quiscalis mexicanus
	Boat-tailed grackle	Quiscalis major
17	Common redpoll	Carduelis flammea
	Hoary redpoll	Carduelis hornemanni

(For the full tables and analysis, see the article, Comprehensive DNA barcode coverage of North American birds. The tables shown here reproduce only a portion of the information in the article.)

So how does this affect birders? Probably not much, at least initially. Headlines for this story excitedly proclaim the discovery of potential new species. In fact, the North American bird list may see a net reduction if all of the proposed changes are accepted by the appropriate committees. Coverage has also suggested that the results, extrapolated to the whole world, may imply an additional 1,000 species to add to the 10,000 already recognized. Again, extrapolating results suggests that some species groups will also be condensed, so it is too soon to predict reaching the 11,000 mark.

This study is was designed as a test of the barcoding methodology, as the authors mention several times. As such, the DNA samples are too small to be used for distinguishing species based on genetics alone. The authors suggest that further DNA analysis will be necessary before any of the recommended splits or lumps are implemented. Even then, genetic analysis is only one factor among many in distinguishing separate species. Interbreeding, behavior, range, and physical appearance are among the other factors considered. There also seems to be some skepticism about the results in the wider birding and ornithological communities, so records committees are likely to move very slowly in acting on the recommendations.

Several other blogs have covered this story, including Search and Serendipity, Hawk Owl's Nest, and Nemesis Bird. There has been extensive discussion of the issue on the ID-Frontiers list. Snail's Tales has an unrelated post on defining species.