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 |
LumpsThe 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 |
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.