Lure of the list: How the American Ornithologists’ Union and American Birding Association determine bird checklists

WHEN I BEGAN SERIOUS, UNRELENTING, all-consuming birding in 1958 at the tender age of 14, I was never without my copy of Roger Tory Peterson’s A Field Guide to the Birds. Once I showed my younger cousin Bruce an Eastern Towhee, he joined me in bird chasing, a lifelong bond we still share.

We lived in the Delaware Valley area, encompassing Philadelphia and parts of New Jersey and Delaware. From Hawk Mountain to Cape May, Bruce and I, transported by our parents and adult birder friends, began building our life lists. It was easy then. We were new to birding, so most birds were new to us. And Peterson made it a snap to keep track because he included a checklist among the first pages of his indispensable field guide.

On a trip to Mill Grove, once the home of Audubon, we checked off Ovenbird, Belted Kingfisher, Spotted Sandpiper, and Baltimore Oriole. A trip to Beach Haven, on the Jersey shore, added Willet and Piping Plover. A spring morning in my Abington backyard brought checks to Bay-breasted and Cape May Warblers and White-crowned Sparrow, to name but a few. Our lists began to fill, and as they did we became ever hungrier for more.

At Churchville Reservoir, where ducks congregated in winter and swallows flocked in spring, we met Gertrude Burrell, a woman with many more years of birding than us. She showed us her Peterson, its pages worn and dog-eared, notations galore along the margins of the plates. But what I recall best was her life list. Virtually every bird appeared to have a bold checkmark next to its name. Wow, were we ever impressed!

Lists have power. They document success in birding, serving as resumes of a sort. Peterson himself recognized the role of lists when he named the second chapter of his 1948 book Birds Over America “The Lure of the List.” And he was right. Lists are the siren call to birding.

Sixty years later, lists continue to lure birders into what can easily become a most pleasant and safe addiction. Birders keep yard lists, year lists, state lists, county lists, world lists, and a few even keep lists of birds seen copulating. Go on eBird and see lists for all parts of North America. Add your own.

Why the fascination? It’s not so much the list, but listing as a process. Listing is birding sport, the very reason for the creation of the American Birding Association. The ABA has been around for 40 years, and listing remains preeminent among its missions.

Lists motivate birders into action. Listing may result in lots of frequent-flyer miles, and it can easily become a monetary and time sink satisfied, indeed justified, only by a momentary good look at a Black Rail or a Zigzag Heron.

Two essential checklists

Just how are lists assembled and what kinds of lists are the most essential?

All North American birders inevitably use two official lists in some form or another. The first is the Check-list of North American Birds published by the American Ornithologists’ Union. The second is the ABA Checklist published by the American Birding Association. Both standardize names and species of North American birds and thus make it possible for birders to record the species they have observed and compare their lists with those of others. Any field-guide author must use the AOU list at least with regard to common and scientific names, and many arrange the birds strictly in AOU taxonomic order. In what ways are the two lists related, and why, in fact, are there two essential lists?

Let’s begin with the AOU list. The AOU was founded in 1883 and is the preeminent scientific ornithological society in this hemisphere. It is the final arbiter of what constitutes a species and what doesn’t. In doing so, the AOU provides official common and scientific names. And the AOU’s mission includes documenting the distributions of all bird species found in North America.

Ever wonder why common names of birds are routinely capitalized, as in Tufted Titmouse? Why not tufted titmouse? It is because the AOU recognizes Tufted Titmouse as the official common name of the species. Its scientific name isBaeolophus bicolor, which was changed from Parus bicolor some years ago, when the AOU adopted a new classification of the titmouse and chickadee family, Paridae.

The AOU has published seven editions of its Check-list since 1886. The most recent, published in 1998, appeared 15 years after the sixth, which came out in 1983. Rather than make the birding and ornithological communities wait for years for news of check-list changes made between editions, the AOU describes them in the form of supplements. Published every other year from 1985 to 2002, the updates now appear annually, usually in the July issue of the AOU’s quarterly journal The Auk.

The AOU’s North American Check-list Committee is the official decision-making body regarding all matters pertaining to the Check-list. It consists of 12 members, each of whom is an expert in avian taxonomy and classification. It is perhaps easiest to think of the NACC as roughly equivalent to the U.S. Supreme Court in matters of whether species should be lumped or split, or whether, for instance, New World vultures should be classified with raptors or storks.

The committee considers proposals from its members and from ornithologists who perform research on taxonomy and classification. Each proposal is voted upon and requires a two-thirds majority to be adopted.

For example, in its 2007 update, the NACC made the following changes:

• Updated the number of species listed to 2,046
• Changed the common name of Anser fabalis from Bean Goose to Taiga Bean-Goose (note the new hyphen) and split the species to now include Tundra Bean-Goose, Anser serriostris
• Changed the scientific name of Belted Kingfisher from Ceryle alcyon toMegaceryle alcyon
• Added Mesophoyx intermedia (Intermediate Egret) along with a description of its habitat and distribution and notes about the species
• Returned the New World vultures to the order Falconiformes (birds of prey) from the Ciconiiformes (storks)

The list above is only partial but provides a clear idea of the sorts of decisions the committee makes. (See “Birding Briefs” for a summary of this year’s changes.)

What concerns most birders, of course, is the lumping and splitting of species. Birders recall with disdain the 1973 lumping of Baltimore and Bullock’s Orioles into Northern Oriole, a decision that was reversed in 1995. And birders applauded the 1997 ruling to divide Solitary Vireo into Blue-headed, Cassin’s, and Plumbeous Vireos, three ticks on the list where once we had but one.

What’s a species?

The AOU admits that species-level decisions are often thorny issues. The guiding principle remains the Biological Species Concept (BSC), in which species are defined (at least in theory) on the basis of reproductive isolation. For example, although Alder and Willow Flycatchers look alike, they sound distinct and recognize each other as unique species. Thus Willows mate with other Willows and Alders with other Alders. For this reason, they qualify as distinct species under the BSC.

But there are difficulties with the BSC. Most obvious is that species do hybridize on occasion, seemingly in defiance of the core concept of the BSC: that they recognize each other as separate. Blue-winged Warblers, for example, readily hybridize with Golden-winged Warblers in the eastern part of their range. And the Black-capped Chickadee hybridizes in part of its range with the Carolina Chickadee, but the hybrid zone is considered sufficiently narrow not to lump the two species. But of course, such decisions are ultimately judgment calls.

Another problem with the BSC is that more and more research using molecular data such as mitochondrial-DNA (m-DNA) is changing our understanding of taxonomy. Experts in the field look to genetic distance, rather than mating preferences or reproductive isolation, to establish relationships among species.

For example, molecular data suggest that Bullock’s and Baltimore Orioles are not each other’s closest relatives, even though they occasionally hybridize. The same is true of Black-capped and Carolina Chickadees. Now scientists are attempting to use molecular markers to barcode bird species and thus determine which species are most closely related.

Their data has driven the development of the Phylogenetic Species Concept (PSC), which is challenging the BSC. The PSC focuses on the most recently evolved traits, including DNA differences, between populations. The resulting genetic distance designates species. Most ornithologists admit that under the PSC, many current subspecies need to be elevated to species status, presumably to the delight of listers.

In contrast to the AOU’s North American Check-list Committee, the ABA’s Checklist Committee (note the absence of a hyphen) has a different mission. It is, first and foremost, not the decision-making body regarding species designations. Indeed, the ABA committee always adopts the AOU’s species-level decisions. Likewise, the ABA always adheres to the AOU’s scientific and common names of birds. Coordination is easy because such well-known birders as Jon L. Dunn and J.V. Remsen, Jr., have served on both committees.

The ABA Checklist area is not the same as that of the AOU, a big difference between the two lists. The ABA area does not include Hawaii, the West Indies, Bermuda, Greenland, or any area south of Mexico. The AOU includes all of those regions up to the border of Panama and Colombia, thus its area is much larger. That’s why the AOU lists more than 2,000 species, while the ABA tallies 947.

Even more important than the area differences are the decisions of which rare-bird records to accept. The AOU normally, but not always, defers to state records committees and to the ABA Checklist Committee.

For example, a Light-mantled Albatross, a seabird of the southern oceans, was identified and extensively photographed off Cordell Banks in central California on July 17, 1994. The identity of the bird was never in doubt.

The AOU included the species in the seventh edition of the Check-list. The ABA, however, did not add the species to the sixth edition of its checklist, published in 2002, because some committee members believed the bird could have arrived with help from a ship.

This led to concerns that ABA standards for vagrancy may be overly strict. No one could provide any solid evidence that the bird was ship-assisted; the argument was utterly hypothetical. The decision was reversed in November 2007, and Light-mantled Albatross was added to the ABA list.

Like the AOU list, the ABA list is constantly updated, and such updates are reported in the ABA’s magazine Birding. Essentially, the AOU gives the ABA primacy regarding the establishment of introduced species as well as acceptance or rejection of vagrant species.

With rare exceptions, such as the Light-mantled Albatross, the two organizations are in harmony.

Global checklists

Other official lists also are essential to birders, at least those who bird around the globe. In May, the AOU issued a revised list of South American birds under the auspices of a 10-member South American Classification Committee. Its mission is to create a standard classification with English names of all species occurring on the continent, including offshore islands such as the Galápagos. The list currently includes 3,260 species and is very much a constant work in progress.

Finally, we have The Clements Checklist of Birds of the World, authored by the late James F. Clements. As the most commonly used global checklist, it is essential to world birders. It lists more than 9,800 species and is currently updated on a regular basis by the Cornell Lab of Ornithology, although it isn’t an official list in the sense of the AOU Check-list.

Checklists are essential for comparative purposes and for documentation of sightings. Because of the lure of the list, amateurs have made immense contributions to the understanding of avian distribution since the first Christmas Bird Counts in the early 1900s. Today, due to the increased use of digital cameras and digiscoping, listing has never been a more powerful tool for establishing distributional records.

Anthony White, chair of the ABA’s Recording Standards and Ethics Committee, makes the strong point that listing has real value to ornithology because it is so tightly linked to the study of species distribution. In the face of climate change and other factors affecting bird habitat, it has never been more essential that birders pay attention to trends and changes in where and when species occur. Further, White asserts that when we bird a new area, we need three things: a field guide, a bird-finding guide (in either book or human form), and an accurate and up-to-date checklist.

John Kricher is Meneely Professor of Biology at Wheaton College, a Fellow in the American Ornithologists’ Union, and a former board member of the American Birding Association. He is past-president of both the Association of Field Ornithologists and the Wilson Ornithological Society and the author of A Neotropical Companion (Princeton, 1999), Galápagos: A Natural History (Princeton, 2006), and other books.

Originally Published September 1, 2008