Shuffling the deck: does this bring clarity or confusion?

Modern avian systematics deals with evolutionary relationships among birds and relies on a combination of morphological, biochemical, biogeographical, vocal and behavioral evidence along with other measurable traits such as the relatedness of ectoparasites. In simple terms, diverse populations of birds can be progressively subdivided at the level of order then family then genus and finally species; each successive category proposing a more granular measures of shared ancestry. The extensive use of gene sequencing has been especially instructive – some might say, explosive – in terms of clarifying the higher-order relationships between the 35 or so orders and more than 230 families that encompass all living birds (Fjeldså 2013, Cracraft

2013). This work is often performed on a scale that requires consortiums of scientists spread across multiple institutions if not the globe, and like an earthquake can violently shake and rearrange the existing dogma about the relationships between birds.

For instance, we’ve already seen the caracaras and falcons wrenched away from the hawks and other diurnal raptors to be placed awkwardly between woodpeckers and parrots. Hold tightly to your binoculars, because the seismic upheavals are not over yet.

Drawing most heavily on the convergent findings of two immense studies by separate research syndicates (Jarvis et al. 2014, Prum et al. 2015), the 57th Supplement lays out a large number of radical higher-level changes, aftershocks following the initial quake. From the standpoint of the Checklist of the Birds of New York State the positions of a whopping fifteen orders of non-passerines and three families of passerines (song birds) are now changed (summarized in the table below and incorporated into the online checklist).

Black Vulture  © Carena Pooth

New World vultures, represented for us by Turkey Vulture Cathartes aura and Black Vulture Coragyps stratus, have always been difficult to place. Although similar to other diurnal raptors (Old World vultures, eagles, hawks and falcons) on a superficial level, vultures exhibit a number of anatomical and behavioral differences from hawks and falcons such as the inability to grasp strongly with their feet and the rather disgusting habit of defecating on their bare legs as a way to cool themselves. When molecular studies by Sibley and Ahlquist (1990) indicated that American vultures, and their cousins the condors, are in fact closely related storks (Ciconiidae), many commentators felt that the puzzle had finally been solved and the revision was adopted by the AOU in 1998. To the chagrin of the “of course they are storks crowd” the AOU reversed its stance in 2007 and moved the New World vultures into the Falcons and Caracaras (Falconiformes)! This too was short-lived and, based on the newer DNA sequencing studies, the New World vultures and condors are now in a separate order (Cathartiformes). This is considered a sister grouping to the hawks and allies (Accipitriformes). Given the uncertainties, the shuffles may continue and indeed affinities to other orders have been noted. The one thing that seems to be clear is that more analysis is needed, either to cement the present taxonomy or support additional changes.

Although based on the latest scientific information, there remains an element of subjectivity in avian systematics with the prospect of continued flux as more information is collected and as our thinking about evolutionary relationships becomes more refined. This is work in progress and it is impossible to know if the latest shuffles will remain in perpetuity or will succumb to further rearrangements. Concerned about this constant reordering and the confusion that results, a cadre of leading field guide authors have pushed for a more user-friendly and stable sequence of bird families and other distinctive taxa or groups that can be used in field guides and related publications (Howell et al. 2009). They don’t disagree with the scientific reasoning for taxonomic overhauls but argue that in field guides, similarities in appearance are more important than the underlying evolutionary relationships and point out that designs that mirror an official taxonomic sequence will soon become outdated.

I’m inclined to agree. Having learned in my youth the classic sequence used by Bruun and Singer (1975), I still find it difficult to flip to the right section of a modern field guide or jump quickly to the right place on a checklist. In the revised Checklist of the Birds of New York State, there are now almost eighty species separating grebes from alcids, which they can resemble, and twice that many between grebes and loons. When struggling to identify a fast diving bird it makes sense to have the main candidates only a page or two apart. Similarly, larks and longspurs are often found in the same habitat and can be mistaken for one another and yet are also widely separated when presented in the current taxonomic order. Why should we need to use the index to find the ever mobile New World vultures? The conversation about whether or not to follow taxonomic order or something more intuitive is for another discussion. However, this is something that everyday birders, the ultimate users of field guides and checklists, should be expressive about.

Buried among these tectonic shifts are a couple of comparatively trivial changes to the list positions within the shorebirds and vireos. The genus Actitis, which for us includes Spotted Sandpiper Actitis macularius, and the Tringa sandpipers, with four representatives on the NYS list, move down to just above the Phalaropes. Further down the list, analysis of nuclear and mitochondrial DNA sequences prompted a major overhaul of the organization of genera and the linear sequence of North American vireos (Slager et al. 2014). As a result, the list positions of Warbling Vireo Vireo gilvus and Philadelphia Vireo V. philadelphicus are swapped.

New genus names for two shearwaters and Sandhill Crane

OK let’s begin with the shearwaters. No armchair lifers for anyone, just recognition of the differences between two of the larger shearwaters: Sooty and Great Shearwater, which become Ardenna griseus and Ardenna gravis, respectively, and the two smaller ‘black-and-white’ shearwaters: Manx and Audubon’s Shearwaters, which remain in the genus Puffinus. This partition seems intuitive and will find ready acceptance with most field birders. It is based on the findings of two molecular studies (Penhallurick and Wink 2004; Austin et al. 2004) and was already recognized by a number of important taxonomies such as that used by BirdLife International (del Hoyo and Collar 2014).

© Angus Wilson

 

In animal cells there are two sets of genetic information, the very large and complex genome that is stored in the nucleus and a much smaller set in the mitochondria. The nuclear genes are contributed by both parents whereas the mitochondrial genes are inherited from the mother only. Mitochondrial genes are favored in molecular phylogenetic studies because they evolve fast enough to accumulate differences between populations that have diverged very recently; however, there are technical biases associated with using mitochondrial rather than nuclear gene sequences (Prychitko and Moore 2000). Both shearwater studies used the same mitochondrial gene and confirmation using nuclear genes is needed. That said, the Ardenna / Puffinus split makes sense in terms of the physical appearance of these species and, is also supported by differences in their geographic distribution. Both Sooty and Great Shearwaters breed on temperate islands in the Southern Hemisphere and migrate across the equator into the North Atlantic during their non-breeding season. Manx Shearwaters, on the other hand, breed in the North Atlantic, predominantly in the British Isles and Iceland, and make a trans-equatorial migration in the other direction. Although not yet proven, some of the Manx Shearwaters seen in New York might come from colonies in Atlantic Canada and nesting is suspected to occur as close as Massachusetts. Audubon’s Shearwater is also an exclusively northern hemisphere breeder, with the majority nesting in the Bahamas and presumably following the Gulf Stream into New York offshore waters. As a side note, the relationship trees cited in these studies suggest that Sooty Shearwater is more closely related to Great Shearwater than to Short-tailed Shearwater (A. tenuirostris), which looks very similar to Sooty Shearwater and is also a southern hemisphere breeder that migrates into the northern hemisphere in austral winter.

Common and Hoary Redpolls survive … for now at least.

Looking ahead, the Supplement notes that a decision on a proposal to bring together (‘lump’) Common (Acanthis flammea) and Hoary Redpolls (A. hornemanni) into one species has been postponed. The decision – if and when it comes – will doubtless be influenced by a 2015 study by Nick Mason and Scott Taylor, researchers in the Lovett group at the Cornell Lab of Ornithology.  Mason and Taylor compared more than 23,000 variable sites in the Redpoll genetic material and found no evidence of prolonged reproductive isolation (Mason and Taylor 2015). This is a really fascinating observation with important ramifications for field identification that beyond the scope of this essay. Suffice to say that if the NACC votes to combine the two species, then the NYS list, which currently stands at 490 species, will be reduced by one!

The last modification impacting the Checklist of the Birds of New York State affects the English name of Alauda arvensis, an introduced species that is now extinct (‘extirpated’) in New York State but retained on the list. This is changed from Eurasian Sky Lark to Eurasian Skylark. Some readers will be aware that this ‘new’ name was already used by the AOU in the 34th to 39th Supplements (1982-1993) but in 1995 was changed to Sky lark and then in 1998 to Sky Lark, with an upper case L. Exciting stuff, eh? Anyhow, Eurasian Skylark seems a wise choice and hopefully it will stay put for a while. It is already used by most global and local taxonomies, is consistent with the names of other lark species and provides distinction from the closely related Oriental (A. gulgula) and Razo Skylarks (A. razae).

In addition to the changes discussed here, there are other changes in the 57th Supplement that will be of interest to traveling birders, including the splitting of Western Scrub-Jay into the more coastal California Scrub-Jay (A. californica) and interior southwestern Woodhouse’s Scrub-Jay (A. woodhouseii). Those who’ve birded in California and in Arizona may well have seen both but so far no Scrub-Jay of any kind has been observed in New York State.

  Angus Wilson
  Chair, New York State Avian Records Committee
  New York State Ornithological Association

LITERATURE CITED

Austin JJ, Bretagnolle V, and E Pasquet. (2004) A global molecular phylogeny of the small Puffinus shearwaters and implications for systematics of the Little-Audubon Shearwater complex. Auk 121: 847-864.

Bruun B and A Singer (1975) The Hamlyn Guide to Birds of Britain and Europe. Hamlyn Publishing Group, London, UK.

Chesser RT, Burns KJ, Cicero C, Dunn JL, Kratter, AW, Lovette IJ, Rasmussen PC, Remsen JV Jr., Rising JD, Stotz DF, and K Winker (2016) Fifty-seventh Supplement to the American Ornithologists' Union: Check-list of North American Birds. The Auk 133:544-560.

Cracraft J (2013) Avian higher-level relationships and classification: nonpasseriformes. Pp xxi-xliv in Dickinson EC and JV Remsen eds (2013). The Howard and Moore Complete Checklist of the Birds of the World. 4th Edition. Volume 1, Non-passerines. Aves Press, Eastbourne, UK.

del Hoyo, J., Collar, NJ, Christie, DA, Elliott, A and LDC Fishpool (2014) HBW and BirdLife International Illustrated Checklist of the Birds of the World. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Dickinson EC, Jemsen JV Jr, and L Christidis (2014) The Howard and Moore Complete Checklist of the Birds of the World. 4th edition. Vol. 1: Non-passerines and Vol. 2: Passerines, Aves Press, Eastbourne, UK

Fjeldså J (2013) Avian classification in flux. Pp 77-146 in: del Hoyo et al. 2013 Handbook of the Birds of the World. Special Volume. New Species and Global Index. Barcelona, Spain and Cambridge UK: Lynx Edicions and BirdLife International.

Howell SNG, O’Brien M, Sullivan BL, Wood CL, Lewington I and R Crossley (2009) The purpose of field guides: taxonomy vs. utility? Birding 41: 44-49.

Jarvis ED et al. (2014) Whole-genome analyses resolve early branches in the tree of life of modern birds. Science. 346:1320-1331.

Krajewski C., Sipiorski JT and FE Anderson (2010) Complete mitochondrial genome sequences and the phylogeny of cranes (Gruiformes: Gruidae). Auk 127:440–452

Mason NA and SA Taylor (2015) Differentially expressed genes match bill morphology and plumage despite largely undifferentiated genomes in a Holarctic songbird. Molecular Ecology 24: 3009–3025.

Penhallurick J, and M Wink (2004) Analysis of the taxonomy and nomenclature of the Procellariiformes based on complete nucleotide sequences of the mitochondrial cytochrome b gene. Emu 104: 125-147.

Prum RO, Berv JS, Dornburg A, Field DJ, Townsend JP, Lemmon EM, and AR Lemmon (2015) A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature 526:569-73.

Prychitko TM and WS Moore (2000) Comparative evolution of the mitochondrial cytochrome b gene and nuclear beta-fibrinogen intron 7 in woodpeckers. Molecular Biology and Evolution 17:1101-11.

Sibley CG and JE Ahlquist (1990) Phylogeny and Classification of Birds: A Study in Molecular Evolution. Yale University Press, New Haven, Connecticut.

Slager DL, Battey CJ, Bryson RW Jr., Voelker G, and J Klicka (2014) A multilocus phylogeny of a major New World avian radiation: The Vireonidae. Molecular Phylogenetics and Evolution 80:95–104.