In early July, many birders eagerly await the annual report of the American Ornithological Society’s Committee on Classification and Nomenclature of North and Middle American Birds. This committee of professional ornithologists is responsible for making decisions on the splitting or lumping of species, changes in common and scientific names of birds and changes in the order in which birds appear in official checklists.

Like any scientists, ornithologists revisit bird identification and classification as more information becomes available. Requests for consideration of thorny taxonomic problems are accepted by the Committee and sometimes the Committee decides to reconsider decisions on their own.

The Committee tends to be conservative, only making changes when the new information is strongly compelling.

Perhaps the most significant decision by the Committee this year was to merge Thayer’s Gull into Iceland Gull. In Maine, Iceland Gulls are regular winter visitors. Like many gulls, adults are white below with gray backs and upper wings. However, Iceland Gulls lack black on the wingtips. Thayer’s Gulls have a similar shape and size to Iceland Gulls but do have black wingtips.  Confusing intermediates do occur.

The Committee recognized Thayer’s Gull as a distinct species in 1973 based on research done on Baffin Island where both Thayer’s Gull and Iceland Gull nest. The researcher claimed that the two types of gulls did not interbreed. This researcher claimed that females used the color of the skin around the eye (the orbital ring) to distinguish male Iceland Gulls from male Thayer’s Gulls. By capturing males and painting the orbital ring to match the other species, the researcher claimed that 55 hybrid matings were produced. His conclusion was that the orbital ring color serves to isolate the two species and prevent interbreeding.

The Checklist-Committee accepted this two-species argument. Subsequently, researchers on Ellesmere Island found that Iceland Gulls and Thayer’s Gull freely interbreed. Furthermore, evidence has surfaced that the original study was sloppy at best and fraudulent at worst. The recent decision to merge Thayer’s Gull into Iceland Gull is warranted in my view. Unfortunately, many of us lose a species on our life list.

Many ornithologists were anticipating a split of Yellow-rumped Warbler. For much of the 20th century, we recognized the Myrtle Warbler as distinct from Audubon’s Warbler. Myrtle nests broadly across Canada and many northern states, including Maine. Audubon’s nest from the Rockies westward from New Mexico to British Columbia.

The two forms are similar but Myrtle has a white throat and Audubon’s has a yellow throat. Based on a study that showed interbreeding of the two forms in a narrow region of overlap in western Canada, the Committee decided to combine the two into a single species, the Yellow-rumped Warbler.

Since then, ornithologists have compared the DNA of different populations. The genetic differences suggest that the two forms are different enough to qualify as separate species. A third species restricted to Guatemala is supported by DNA differences as well as plumage differences.

In a surprise, the Check-list Committee turned down the proposal and continues to recognize the Yellow-rumped Warbler as a broadly distributed species.

The conservative nature of the Committee was evident in other decisions as well. Other proposed changes that were rejected included the split of Willet into two species, the split of Brown Creeper into two species and the lumping of Common Redpolls and Hoary Redpolls.

A proposal to change the common name Ring-necked Duck to Ring-billed Duck was turned down as well. The ring on the bill is much more obvious than the ring on the neck.

Based largely on DNA comparisons, we now know that Yellow-breasted Chat is not a warbler. It is now in a separate family, the Icteriidae. New World sparrows are placed in their own family, the Passerellidae, separate from the Old World Buntings, the Emberizidae.


[First published on July 16, 2017]