Charadriiformes

The 44 Orders

Paleognaths

Galloanserae

Metaves

Pelecanae

Charadriae

Passerae

CHARADRIAE

CHARADRIIFORMES

There is a single order in Charadriae, the Charadriiformes. The Charadriiformes include 22 families, with 94 genera and 371 species ranging from shorebirds to gulls to alcids. The Charadriiformes have been carefully studied in recent years and DNA methods have proven especially effective at unraveling the taxonomy. We not only know how the various families relate, but we also have a good handle on many of the genera (the large white-headed gulls continue to puzzle).

There is a lot of evidence for monophyly of the Charadriiformes as consituted here (e.g., Ericson et al., 2003a; Paton et al., 2003; Cracraft et al., 2004; Thomas et al., 2004a; Paton and Baker, 2006; Baker et al., 2007; Fain and Houde, 2007). Other than arguments about the Herring Gull complex, the taxonomy of this order is now pretty well worked out. Many studies have found that gulls and alcids are closely related to the shorebirds. Collectively, these analyses have made it quite clear that the sandgrouse (Pteroclidae) and bustards (Otididae) are not Charadriiformes. They have also shown that the buttonquail (Turnicidae) and Plains-wanderer (Pedionomidae) are Charadriiformes. The position of the buttonquail is also supported by morphology (Mayr, 2008).

To help make the taxonomy clear, the Charadriiformes have been divided into 5 suborders: Chionidi, Charadrii, Scolapaci, Turnici, and Lari. The 2 page genus-level Charadriiformes tree, shows how it fits together. To improve clarity, the tree includes only the suborders, families, and genera (no subfamilies or tribes).

Click for Charadriiformes tree
Click for Charadriiformes tree

Chionidi

Pluvianellidae: Magellanic Plover

1 genus, 1 species Not HBW Family

Chionidae: Sheathbills

1 genus, 2 species HBW-3

Burhinidae: Thick-knees

2 genera, 10 species HBW-3

Charadrii

Pluvianidae: Egyptian Plover

1 genus, 1 species Not HBW Family

Although it is sometimes put in its own family, the Egyptian Plover is typically considered a member of the Glareolidae (pratincoles and coursers). Ericson et al. (2003a), Baker et al. (2007), and Fain and Houde (2007) make clear it is nowhere close to the Glareolidae. All three found it to be basal in the Charadrii (in our sense). Further, all found it to be sister to the remaining Charadrii, which justifies placing it in its own family.

Pluvialidae: Golden-Plovers

1 genus, 4 species Not HBW Family

One big surprise to come out of the molecular data is that the Golden-Plovers (and Black-bellied) are not so closely related to the rest of the plovers. They are actually closer to the stilts, avocets, oystercatchers, and ibisbill (Ericson et al., 2003a; Baker et al., 2007; Fain and Houde, 2007).

Recurvirostridae: Stilts, Avocets

3 genera, 9 species HBW-3

Ibidorhynchidae: Ibisbill

1 genus, 1 species HBW-3

Haematopodidae: Oystercatchers

1 genus, 12 species HBW-3

Charadriidae: Plovers, Dotterels

10 genera, 63 species HBW-3

The taxonomic status of the Kentish-Snowy Plover complex has been controversial. Recent work by Küpper et al. (2009) found that the Kentish, Snowy, and White-fronted Plovers represented independent groups, with little or no evidence of gene flow between them. Not only does this separation appear to be long-standing, but the White-fronted Plover seems to be more closely related to the Kentish Plover than to the Snowy Plover. Accordingly, the Kentish (C. alexandrinus) and Snowy (C. nivosus) Plovers are treated as separate species below.

Scolapaci

Pedionomidae: Plains-wanderer

1 genus, 1 species HBW-3

Thinocoridae: Seedsnipes

2 genera, 4 species HBW-3

Rostratulidae: Painted-snipes

2 genera, 3 species HBW-3

Jacanidae: Jacanas

6 genera, 8 species HBW-3

Whittingham et al. (2000) found two clades of Jacanas, one containing Hydrophasianus and Jacana, the other consisting of the other four genera.

Scolopacidae: Sandpipers, Snipes

21 genera, 95 species HBW-3

Scolopacidae tree The overall treatment of the sandpipers relies heavily on Baker et al. (2007). It is generally consistent with the results in Ericson et al. (2003a), Fain and Houde (2007), Paton et al. (2003), and Thomas et al. (2004a) as well the more heterogeneous evidence assembled by Thomas et al. (2004b). The Tringa sandpipers use the arrangement in Pereira and Baker (2007), which was also adopted by the AOU and BOU lists in 2007.

The curlews and Upland Sandpiper form the basal group (Numeninae), followed by the godwits. The remainder (Scolopacinae) then divides into three groups as in the diagram. Although the correct position of Aechmorhynchus and Prosobonia is unknown, making them a basal group in Tringini seems the best bet.

It has long been suspected the Surfbird is close to the knots (e.g., Jehl, 1968). This is exactly what Bororwik and McLennan (1999) found in their DNA tree. Indeed, their results suggest the Surfbird and knots are congeneric. The other “Calidris” are more distantly related, and the old genus name Ereunetes has been applied to them, including the Buff-breasted.

My use of Borowik and McLennan (1999) is somewhat limited. Their tree is presented as a tool, but the tree itself is not really analyzed in their paper. Although I'm still willing to accept their results when they confirm previous suspicions, I'm not willing to accept them when they imply novel changes in the rest of the ‘calidrines’ (Ereunetes) without having some additional evidence.

The New Zealand Snipes are now considered to include 4 exant and recently extinct species based on Baker et al. (2010) and Worthy et al. (2002). The Snares and South Island Snipes are quite closely related, with an estimated divergence time of about 50,000 years. Their status as separate species rests on the lack of an aerial display for the Snares Snipe, as well as genetic and plumage differences. The Subantarctic and Chatham Snipes are somewhat more distant relatives.

Numeniinae: Curlews

Limosinae: Godwits

Scolopacinae: Sandpipers, Snipes, Woodcock

Scolopacini: Snipe and Woodcocks

Tringini: Phalaropes and Shanks

Arenariini: Turnstone and Stints

Turnici

Turnicidae: Buttonquail

2 genera, 17 species HBW-3

Lari

Glareolidae: Coursers, Pratincoles

4 genera, 17 species HBW-3

Dromadidae: Crab Plover

1 genus, 1 species HBW-3

Stercorariidae: Skuas, Jaegers

1 genus, 7 species HBW-3

Alcidae: Auks

11 genera, 24 species HBW-3

The taxonomy follows Baker et al. (2007) and Pereira and Baker (2008). Thomas et al. (2004a) places Synthliboramphus more basally.

Rynchopidae: Skimmers

1 genus, 3 species HBW-3

Sternidae: Terns

12 genera, 46 species HBW-3

The tern taxonomy is based on Bridge et al. (2005), which places Anous and Gygis firmly in the Sternidae. In contrast, Baker et al. (2007) found Anous and Gygis to be basal to the gulls, terns, and skimmers. However, this may be due to problems with the Anous DNA used. Baker et al. also found a rather different arrangement of the tern genera. For the present, I'm sticking with Bridge et al. because they sampled many more tern species than Baker et al. The whole gull/tern/skimmer complex seems to need more study.

The American Sandwich Terns are split under the old name Cabot's Tern, Thalasseus acuflavidus. Efe et al. (2009) found that Cabot's Tern is more closely related to Elegant Tern than to Old World Sandwich Terns. They also found that no systematic genetic distinction between Cayenne and Cabot's Terns and question whether eurygnathus is distinct from acuflavidus.

Laridae: Gulls

11 genera, 56 species HBW-3

At the generic level, the taxonomy of the gulls follows Pons et al. (2005), which gives the most complete treatment. Their results are generally consistent with Crochet et al., (2000) and were quickly accepted by AOU and BOU. One noteworthy feature is the use of separate genera for masked gulls (Chroicocephalus), hooded gulls (Leucophaeus), and black-headed gulls (Ichthyaetus). The large white-headed gulls remain in Larus. Within Larus, the band-tailed gulls (pacificus, belcheri, atlanticus, and crassirostris) may also deserve generic recognition (Gabianus?), although the evidence is less strong here.

Starting with Western Gull, we run into a taxonomic maze, the large white-headed Larus gulls — the herring gulls. The herring gull clade involves over 30 very closely related taxa, not all of them yet named. They seem to have differentiated quite recently, with the common ancestors of all herring gulls living perhaps 300,000 years ago. Some of these taxa may still be in the process of speciation, and the genetic differences between them are very small. In fact, the genetic distances are small enough that the basal member of the clade, the Western Gull, hybridizes fairly freely with one of its most distant relatives, the Glaucous-winged Gull. In spite of this, many of the other taxa either do not interbreed, or do so only infrequently, and hence represent distinct biological species.

The papers by Liebers et al. (2001, 2002, 2004), de Knijff et al. (2001), Crochet et al. (2002), Pons et al. (2004), and Gay et al. (2005) focus on the big white-headed gulls. Gull relationships are somewhat obscured by past and recent hybridization, and species limits within the herring gulls remain controversial. In spite of this, a coherent picture is being teased out.

The Yellow-footed Gull and Western Gull (both races) are likely sisters, and are likely sister to the main group of herring gulls. The Ring-billed Gull appears to be the closest relative to the whole clade, including Western and Yellow-footed. This suggests that the ur-herring gulls originated in North America. A group found its way east into Europe and split into two clades, possibly corresponding to glacial refugia (clades I & II in Liebers et al., 2004). The west European clade includes the Great Black-backed, European Herring, Armenian, and Yellow-legged Gulls. The rest are in an Aralo-Caspian clade.

The Caspian Gull (cachinnans only) is basal in the Aralo-Caspian clade, which again splits into two. The first includes Lesser Black-backed Gull (including heuglini, taimyrensis, and barabensis). The Kelp Gull apparently derives from the Lesser Black-backed. The other clade spread eastward into Siberia. This is as far as Liebers et al. give detailed information, as their sampling had very limited coverage of East Siberian and North American species.

Crochet et al. (2002), Pons et al. (2004), and Gay et al. (2005) did sample the North American species. As all three analyzed the same two genes, the results are not independent. None included vegae, and several taxa remain poorly resolved. They all show Glaucous Gull in the North American group. However, due to past hybridization, it remains unclear which clade the Glaucous Gull belongs to—whether it is part of the North American group or close to argentatus. I'm guessing the argentatus relationship is recent hybridization, but my confidence in this is pretty low. In fact, my confidence in this section of the tree is low enough that I leave it unresolved on the diagram.

It had once been thought that the Herring Gull was a ring species that had spread around the world. However, the herring gulls are actually a number of biological species, making the ring species story incorrect. However, some of the herring gulls do interbreed (promiscuously in the case of occidentalis and glaucescens), and the ring species story has a kernel of truth in it. In fact, as the herring gulls spread from North America (occidentalis) around the world we get to glaucescens, completing a ring of many species. In the ring species story, the birds interbreed locally around the ring, with the ends infertile. Ironically, reality gives us a bizzaro-world version of the ring species, where the steps of the ring interbreed infrequently or not at all, and the two endpoints interbreed freely.

A second ring may be forming in the other direction between graellsii Lesser Black-backed and American Herring Gulls as graellsii invades North America.

Some of the species limits among the herring gulls remain contentious. E.g., see Pittaway (1999) and Weir et al. (2000) concerning whether glaucoides, kumlieni, and thayeri are one, two, or even three species. For the present, I am following AOU on this (two). Other named taxa in Liebers's clade II sometimes considered species include (West) Siberian Gull (heuglini and maybe taimyrensis), Baltic Gull (fuscus), Steppe Gull (barabensis), and Mongolian Gull (mongolicus). They also suggest two types of Glaucous Gull, which may not match traditional subspecies, and two types of European Herring Gulls that definitely don't match traditional subspecies. There's also a question concerning whether the Yellow-legged Gull should be split into Mediterranean Yellow-legged Gull (michahellis), Atlantic Yellow-legged Gull (atlantis) and possibly even Cantabrican Yellow-legged Gull (lusitanius?).

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