The 46 Orders










ARDEAE Wagler, 1830

Although the Jarvis et al. (2014) tree suggests that the Eurypgimorphae belong with the Aequornithes, support for this is a little soft. For that reason I have put them in separate superorders.

EURYPYGIMORPHAE Fürbringer, 1888

Traditional classifications of the tropicbirds have usually focused on the totipalmate feet and grouped them with the traditional Pelecaniformes. The Pelicaniformes also have totipalmate feet: frigatebirds, boobies, anhingas, cormorants, and pelicans. The tropicbirds have long been recognized as being somewhat different. More recently, the pelicans and fregatebirds have also been considered a bit different. Morphological analyses continued to show this even in the phylogenetic era. Cracraft (1985) considered the tropicbirds different enough that he divided the Pelicaniformes into two suborders: Phaethontes (tropicbirds) and Steganopodes (the rest). He further separated the frigatebirds as a infraorder and pelicans as a superfamily, leaving the boobies, cormorants, and anhingas more closely grouped. There is a lot of truth to this sort of arrangement.

However, what it misses is that the totipalmate birds are not a natural group! Hedges and Sibley (1994) used DNA hybridization to argue that not only did the pelicans and frigatebirds not belong with the group, but that the tropicbird also didn't belong.

In fact, their Figure 2 is quite interesting. If you try to map it onto the tree I'm using, you find that the tropicbirds are outside the Aequornithes entirely. More recent DNA analyses based on sequences usually put the frigatebirds (but not pelicans) in a group with the boobies, gannets, cormorants, and darters. We follow that here.

More recent genetic studies, such as that of van Tuinen et al. (2001) have more decisively broken up the totipalmate group. In particular van Tuinen et al. correctly placed the pelicans close to the Hamerkop and Shoebill. The various studies supporting Metaves, including Fain and Houde (2004), Ericson et al. (2006a), and Hackett et al. (2008), all included the tropicbirds in Metaves, well separated from the rest of the totipalmate birds. They also all supported a close relationship between the Hamerkop, Shoebill, and pelicans.

Nonetheless, there were still problems with the tropicbirds. Using complete mitochondrial genomes, Gibb et al. (2013) found the tropicbirds nowhere near the rest of the “Pelicaniformes”. McCormack et al. (2013) placed the topicbirds near the Kagu in a grouping reminiscent of Metaves (but different). Finally, the data-intensive analysis by Jarvis et al. (2014) found that Eurypygiformes and Phaethontiformes were sister orders, with 100% bootstrap support. Moreover, they placed the Kagu/Sunbittern/tropicbird group sister to Aequornithes, as is done here.

The arrangement in Jarvis et al. (2014) suggests that totipalmate feet developed at least three times: in the tropicbirds, pelicans, and Suliformes.

EURYPYGIFORMES Fürbringer, 1888

These two monotypic families form a strongly supported clade in Hackett et al. (2008). Their affinities have long been unclear. They had recently been grouped near the cranes, but that appears incorrect. Ericson et al. (2006a) put them in Metaves near Columbea while Hackett et al. (2008) had them sister to the Strisores (also in Metaves). However, Jarvis et al. (2014) have them sister to the tropicbirds and near the waterbird group, Aequornithes.

Rhynochetidae: Kagu Carus, 1868

1 genus, 1 species HBW-3

Eurypygidae: Sunbittern Selby, 1840

1 genus, 1 species HBW-3


Phaethontidae: Tropicbirds Brandt, 1840

1 genus, 3 species HBW-1


The remainder of the Ardeae are in the waterbird clade, Aequornithes. Gibb et al. (2013) use the term “water-carnivore” to describe the birds in this clade. The Aequornithes include 8 closely related orders: Gaviiformes (loons), Sphenisciformes (penguins), Procellariiformes (petrels and shearwaters), Ciconiiformes (storks), Suliformes (frigatebirds, boobies, cormorants, darters), Plataleiformes (ibis), Pelecaniformes (pelicans, hamerkop, shoebill), and Ardeiformes (herons).

There is a lot of support for grouping these birds together (e.g., Cracraft et al, 2004; Ericson et al., 2006a; Gibb et al., 2007, 2013; Hackett et al, 2008; Morgan-Richards et al, 2008), Jarvis et al. (2014).


Gaviiformes has been attributed to Wetmore & Miller, 1926, but Coues had already used Gaviae as a suborder in the second edition (1903) of his “Key to North American Birds” (pg. 1047). The term Colymbiformes has also been used. However, the ICZN eventually suppressed the genus Colymbus due to confusion about whether it applied to loons or grebes. Because of this, I have not tried to attribute priority to some earlier form of the order based on Colymbus, even though some case may be unambiguous. An account of this may be found on Wikipedia's Loon page.

Gaviidae tree

Sprengelmeyer (2014) found that the Red-throated Loon is very distantly separated from the other loons. He estimated the age of the most recent common ancestor as 21.4 million years ago, whereas the most recent common ancestor for the other four loons was only estimated at 8.2 million years ago.

Gaviidae: Loons J.A. Allen, 1897 (1840)

1 genus, 5 species HBW-1


Spheniscidae: Penguins Bonaparte, 1831

6 genera, 19 species HBW-1

The penguin taxonomy follows Baker et al. (2006). Ksepka and Thomas (2012) add some morphological data. They obtained an almost identical topology, differing only in the branching order within Eudyptes.

Although the members of the pairs Macaroni/Royal and Snares/Fiordland are considered separate biological species, the pair Little/White-flippered are not. Christidis and Boles (2008) opined that it was premature to split them, and subsequent analysis have proven them correct. The complicated situation of the Little Penguin is analyzed in detail by Puecker et al. (2009), and I suspect it is not the last word on this. They found two clades, as did previous workers. However, they sampled many more penguins and found the clades did not divide as expected. In particular, there is no support for treating the White-flippered Penguin, Eudyptula minor albosignata as a separate species. Rather, there is a mostly Australian clade (with some New Zealand birds mostly from Otago and Omaru), and a clade covering the rest of New Zealand. Although most of the birds at Omaru seem to group with the Australian E. m. novaehollandiae, not all do. It appears likely that the type of E. m. minor, which is from Dusky Sound, belongs to the New Zealand clade. The significance of the presence of Australian clade birds at Otago/Omaru is yet to be fully understood. E.g., is there interbreeding? If so, how much? Although some uncertainty remains, it looks like two species are involved. The name Little Penguin has been official in Australia for some time, while Blue Penguin has been used in New Zealand, so it makes sense to call them Little Penguin, Eudyptula novaehollandiae, and Blue Penguin, Eudyptula minor.

More recently, Grosser et al. (2015), studying DNA from modern penguins, found that the Austalian lineage penguins in New Zealand were recent arrivals, probably within the last 1500 years. Then Grosser et al. (2016) sampled bones from 146 prehistoric penguins found in New Zealand. The bones prior to 1500 AD all came from Blue Penguins. The Australian lineage Little Penguins did not show up until sometime after 1500. They speculate that a population decline of the native Blue Penguins following the arrival of humans created an opening for Little Penguins to colonize the island.

The Macaroni/Royal and Snares/Fiordland pairs breed on different islands. The differences in appearance and DNA to are sufficient to allow treatment as separate species. In fact, the DNA difference seems to be less than between the Eudyptula clades (Baker et al., 2006), but the Eudyptula plumage differences are smaller and the situation on the breeding grounds is unclear.

Jouventin et al. (2006) make a good case for splitting Rockhopper Penguin into two biological species. I did not find the case for a three-way split compelling (Banks et al, 2006).


The arrangement of the Procellariiforme families follows Prum et al. (2015). A number of sources have been consulted concerning the species sequence. Austin (1996), Austin et al. (2004), Kennedy and Page (2002) and Penhallurick and Wink (2004) were generally useful in organizing the Procellariiformes. Concerning the latter, the comments by Rheindt and Austin (2005) should be noted. Prum et al. (2015), Welch et al. (2014), and Gangloff et al. (2012) were helpful concerning the Procellariidae.

Diomedeidae: Albatrosses G.R. Gray, 1840

4 genera, 21 species HBW-1

Traditionally, the 24 recognized albatross taxa have been grouped into 13 species.

Traditional Albatross Species Limits

24 taxa, 13 species

  • Laysan Albatross, Phoebastria immutabilis
  • Black-footed Albatross, Phoebastria nigripes
  • Waved Albatross, Phoebastria irrorata
  • Short-tailed Albatross, Phoebastria albatrus
  • Royal Albatross, Diomedea epomophora
    • Diomedea epomophora sanfordi
    • Diomedea epomophora epomophora
  • Wandering Albatross, Diomedea exulans
    • Diomedea exulans dabbenena
    • Diomedea exulans amsterdamensis
    • Diomedea exulans antipodensis
    • Diomedea exulans gibsoni
    • Diomedea exulans exulans
  • Sooty Albatross, Phoebetria fusca
  • Light-mantled Albatross, Phoebetria palpebrata
  • Yellow-nosed Albatross, Thalassarche chlororhynchos
    • Thalassarche chlororhynchos chlororhynchos
    • Thalassarche chlororhynchos carteri
  • Grey-headed Albatross, Thalassarche chrysostoma
  • Black-browed Albatross, Thalassarche melanophris
    • Thalassarche melanophris melanophris
    • Thalassarche melanophris impavida
  • Buller's Albatross, Thalassarche bulleri
    • Thalassarche bulleri bulleri
    • Thalassarche bulleri platei
  • Shy Albatross, Thalassarche cauta
    • Thalassarche cauta cauta
    • Thalassarche cauta steadi
    • Thalassarche cauta eremita
    • Thalassarche cauta salvini

Robertson and Nunn (1998) suggested a radical new taxonomy for albatrosses, elevating all 24 taxa to species level. This has caused a certain amount of controversy, and has not been universally accepted (e.g., Penhallurick and Wink, 2004; Penhallurick, 2012). The 4th edition of the highly regarded Howard and Moore checklist (Dickinson and Remsen, 2013) also continues to follow traditional albatross taxonomy. Their version is shown above.

Nonetheless, many other sources have moved toward the Robertson and Nunn taxonomy, and the TiF list uses a 21 species version. IOC 3.3 uses the same 21 species list as TiF. BirdLife International (ver. 5) additionally splits T. cauta and T.steadi for 22 species. The AOU's SACC has adopted the 3-way split of Thalassarche cauta used here (see proposals #155 and #255. Clements 6.7 accepts only this split and uses a 15 species list. The SACC also considered splitting Diomedea exulans into 4 species (see proposal #388). This was unable to gain the required 2/3's majority (the vote was 6-4 in favor of the split). Penhallurick (2012) makes a case for retaining the traditional classification.

How to treat slightly differentiated allopatric taxa, where the breeding ranges do not overlap, is often a thorny issue. If you read SACC proposal #388, you will see just how contentious it is.

My take on it is that there is some evidence of restricted gene flow between many of these taxa—a sign of legitimate biological species. Although the evidence is a long way from being convincing, I think it is enough to barely tip the scale in favor of the 21-species treatment below, at least for the present.

Burg and Croxall (2004), Bried et al. (2007), and Rains et al. (2011) provided support for most of the Robertson and Nunn splits in the Wandering Albatross group (except for D. antipodensis gibsoni), while Burg and Croxall (2001) examined the Black-browed/Gray-headed Albatross group. The Shy Albatrosses were studied by Abbott and Double (2003a, b). Interestingly, the Wandering Albatross in the narrow sense remains widespread even after the other taxa in the group (Tristan, Antipodes, and Amsterdam Albatrosses) are split off.

The phylogeny used here is based on Nunn and Stanley (1998) and Chambers et al. (2009). Finally, the term platei is often used for the northern populations of Buller's Albatross. It is said to refer instead to a juvenile of the southern population, in which case a new name is needed for the northern population (e.g., Chambers et al., 2009).

Oceanitidae: Southern Storm-Petrels Forbes, 1882

5 genera, 9 species Not HBW Family

Oceanitidae tree

The split of the Storm-Petrels into two families was suggested by Nunn and Stanley (1998). See also Hackett et al. (2008) and Prum et al. (2015).

I've added the Pincoya Storm-Petrel, Oceanites pincoyae, described by Harrison et al. (2013).

I've also added the New Zealand Storm-Petrel, which was rediscovered in 2003 (Gaskin and Baird, 2005; Stephenson et al, 2008a). Details of the capture of one are on the Pterodroma Pelagics web site. Some uncertainty remained as to its identity after the initial reports, but a comparison with museum specimens (Stephenson et al, 2008b) removed any doubt that it was a New Zealand Storm-Petrel. A recent genetic analysis by Robertson et al. (2011), based partly on data from Nunn and Stanley (1998), showed that it belongs in genus Fregetta rather than the monotypic Pealeornis.

Robertson et al. (2011) also found that the Fregetta race leucogaster, often considered a subspecies of the White-bellied Storm-Petrel, is actually much more closely related to the Black-bellied Storm-Petrel. Whether it is a subspecies or distinct species is unclear at this point.

Hydrobatidae: Northern Storm-Petrels Mathews, 1912-13 (1865)

4 genera, 17 species HBW-1

The Hydrobatidae have been rearranged based on Nunn and Stanley (1998), Penhallurick and Wink (2004), and Sausner et al. (2016). This entails moving the Fork-tailed Storm-Petrel, Oceanodroma furcata, to the genus Hydrobates. Since O. furcata is the type species of Oceanodroma, and Hydrobates (Boie, 1822) has priority over Oceanodroma (Reichenbach, 1852), the name Oceanodroma must be given up.

One option would be to put the entire family in Hydrobates, as in H&M-4. I find it more helpful to treat each of the four clades as a separate genus. Fortunately, the supply of available names is more than adequate. Those that are relevant are Cymochorea (Coues 1864, type leucorhoa) and Halocyptena (Coues 1864, type microsoma), and Thalobata (Matthews and Hallstrom 1943, type castro).

I've grouped melania and matsudairae together as they are sometimes considered conspecific. That pair is sister to the microsoma/tethys pair, and all join Halocyptena. I've also grouped two other possibly conspecific pairs, tristrami and markhami, and monorhis and leucorhoa. Sausner et al. (2016) found that homochroa is close to leucorhoa, and that hornbyi is basal in this group. All of these go in Cymochorea.

That brings us to the basal group, the contentious Band-rumped (Madeiran) Storm-Petrel, Thalobata castro. Traditionally, it has been thought almost undifferentiated across the Atlantic and Pacific. Now we find that the genes reveal both substantial geographic and seasonal structure, enough that some recommend dividing it into a number of species (see Bolton (2007); Bolton et al., 2008; Friesen et al., 2007; Smith and Friesen, 2007; Smith et al., 2007).

In several locations, Band-rumped Storm-Petrel breeds in both the hot and cool seasons. Recent studies have found that the hot-season population is different from the cool-season population (e.g., Bolton, 2007; Frisen et al., 2007). The following table shows the island groups where Band-rumped Storm-Petrels breed, the season they breed, and applicable subspecific names. There may also be a population breeding on or near Sao Tome, but breeding sites have never been located. Further, it is unknown how closely the St. Helena and Ascension birds are related.

The breeding locations and seasons are:

Location Season Subspecies TiF Species
Ascension &
St. Helena Islands
hot helena castro
Azores hot monteiroi monteiroi
castro castro
Cape Verde Islands protracted
jabejabe jabejabe
Galapagos Islands both bangsi cryptoleucura
Hawaiian Islands hot cryptoleucura cryptoleucura
Japan hot kumagai cryptoleucura

Because they breed in the same location, there is a tendency to think of these as sympatric populations. Since they don't interbreed, they must be distinct species. QED.

Some have even suggested that castro be restricted to the birds breeding in Madiera (Desertas and Selvagem) during the hot season. The rest would be separated as Grant's Storm-Petrel, which does not yet have a scientific name. I find this hard to swallow. Based on Friesen et al. (2007) and Smith et al. (2007), the genetic distances appear to be quite small. Any separation between them is quite recent, perhaps within the Holocene.

Although Friesen et al. (2007) suggest the ancestral birds bred in the hot season, I don't really see this. The Cape Verde population is sister to the others and has a prolonged breeding season. If the ancestral population spread from there, one could easily see it adapting to local conditions that variously support breeding in the hot and/or cool seasons.

This suggests that considering them as sympatric gives the wrong impression. Rather, these populations occupy different niches that in some cases are separated temporally rather than geographically. They are better regarded as being adjacent (or even isolated) rather than overlapping.

This changes the picture. If we think of these populations as potential allospecies, they may not make the grade. There's not much differentiation. More evidence is needed, and there is more for some populations. Bolton (2007) used tape playback to explore whether there are pre-mating barriers to interbreeding. He investigated populations on the Cape Verde, Galapagos, and Azores islands. Although birds responded to calls of birds from their own islands, response to birds from other islands was weak and often no more than to unrelated control species.

This suggests that at least the subspecies tested — jabejabe (Cape Verde), bangsi (Galapagos), monteiroi (Azores hot season), and castro (Azores cold season only) — are distinct biological species. What about the other populations? We first consider the remaining Atlantic populations. Table 3 in Smith et al. (2007) addresses this issue. It shows that the northern Atlantic populations other than monteiroi are quite closely related (estimated divergence times from 100(!) to 17,000 years). Accordingly, I keep them all in T. castro. It also suggests that the birds from Ascension (and St. Helena?) are fairly close to the main populations of castro (divergence time 15,000-30,000 years, as opposed to about 100,000 years between monteiroi and castro, and 200,000-300,000 between jabejabe and either castro or monteiroi). Accordingly, I also treat helena as a form of T. castro.

Click for Storm-Petrel tree
Click for Storm-Petrel tree

That brings us to the Pacific populations. We start with the hot and cool season breeders at the Galapagos Islands. Bolton (2007) found they did not respond to the calls of band-rumped storm-petrels from the Atlantic. Moreover, Smith et al. (2007) found divergence times of over 200,000 years between them and the Atlantic breeders. Finally, Smith and Friesen (2007) found only weak evidence that these involve a cryptic species, and suggested they are only as distinct from each other as subspecies. Here they are treated as part of the same species, distinct from the Atlantic species. The analysis of Freisen et al. (2007) found that the Japanese and Galapagos breeders form a separate clade. Returning to Table 3 of Smith et al. (2007), we also see that the Hawaiian breeders belong in this group. Moreover, the divergence time of 150,000-200,000 years does not compel us to treat them as separate species from each other in the absence of further evidence. Accordingly, I treat the Pacific populations of band-rumped storm-petrels as a single species, T. cryptoleucura, including bangsi (Galapagos) and kumagai (Japan).

When all is said and done, I treat the band-rumped storm-petrels as 4 species. These species are separated not only by breeding location, but by whether they breed in the hot or cool season. In some cases there is little genetic differentiation between hot or cool season breeders, or across islands. When there is no other evidence they form separate species, those populations are lumped together, either as T. castro or T. cryptoleucura.

The Leach's complex has also come under increased scrutiny. Townsend's Storm-Petrel, Cymochorea socorroensis, and Ainley's Storm-Petrel, Cymochorea cheimomnestes, have been split from Leach's Storm-Petrel, Cymochorea leucorhoa, based on a combination of Ainley (1980), Howell (2012), Adams et al. (2016), and the discussion in the proposal that was adopted in the 57th supplement to the AOU checklist.

Howell (2012) has raised the issue of whether chapmani should be treated as a separate species. It's generally considered that it's part of a cline with other Leach's Storm-Petrels on the Pacific coast. There's also a question of whether the Pacific Leach's are conspecific with the Atlantic Leach's. The name leucorhoa has a type locality off Picardy (France), and so applies to the Atlantic birds, while beali (type locality Sitka, Alaska) has very narrow priority for the Pacific Leach's, even if chapmani is included. Priority! (Dickinson et al., 2011) dates beali to March 20, 1906 (second 1906 issue of Condor) and chapmani to April 5, 1906 (second 1906 issue of Auk).

Leach's calls are apparently quite similar between the Atlantic and Pacific. Bicknell et al. (2012) found a small continuing gene flow from the Pacific to Atlantic (but not vice-versa) and estimated the main divergence between them at about 13,000 years ago, which does not suggest species status. To me, the amount of haplotype diversity is surprising for such a small difference (see Figures 1 and 3), and I suspect that the two have been substantially independent for much longer. I think beali probably deserves at least subspecies status.

Procellariidae: Petrels, Shearwaters Leach, 1820

16 genera, 98 species HBW-1

Click for Procellariidae tree
Click for Procellariidae tree

The higher-level relationships within the Procellariidae remain somewhat murky. I've used Prum et al. (2015) as a backbone, and rerooted the tree from Welch et al. (2014) to provide the rest of the structure. The result is also compatible with Gangloff et al. (2012). The taxa shown in brown are subspecies that may deserve species status.

In the new arrangement, the Fulmarinae are the basal group. The Northern Fulmar, Fulmarus glacialis, has been split into the Atlantic Fulmar, Fulmarus glacialis and the Pacific Fulmar, Fulmarus rodgersii, based on Kerr and Dove (2013), who estimated their most recent common ancestor ocurred about 3 million years ago. Although the separation was clear enough in mitochondrial DNA, it didn't show in nuclear DNA. Presumably they simply looked a slow-evolving gene.

Fulmarinae: Fulmars Bonaparte, 1853

Pelecanoidinae: Diving-Petrels and Prions G.R. Gray, 1871 (1850)

The Kerguelen Petrel, Aphrodroma brevirostris is rather uncertainly placed in the basal position here.

The Pelecanoides diving-petrels are traditionally considered a separate family from the petrels (Procellariidae). In many ways, including size, shape, and flight style, they are a southern counterpart of the smaller auks. However, Prum et al. (2015) found them embedded within the Procellariidae.

The Prions and Blue Petrel form the remainder of this group.

Pterodrominae: Gadfly Petrels Verheyen, 1958 (1856)

Among the Petrodroma, I've elevated the Desertas Petrel, Pterodroma desertas to species status based on Zino et al. (2008) and Jesus et al. (2009). Note that the extinct St. Helena Petrel, Pterodroma rupinarum has now been sequenced by Welch et al. (2014) and found to belong to Pterodroma rather than Pseudobulweria.

More recently, the Gray-faced Petrel, Pterodroma gouldi, has been split from Great-winged Petrel, Pterodroma macroptera. See Woods et al. (2016). Note that these are not sister taxa.

Procellariinae: Petrels and Shearwaters Leach, 1820

The division of Puffinus into species is based on Austin et al. (2004). Since it is doubtful that the two clades of Puffinus (here called Ardenna and Puffinus) are more closer related to each other than to Calonectris, they are placed in separate genera.

The Calonectris shearwaters have been studied by Gómez-Díaz et al. (2006). They found that the three Atlantic taxa, borealis, diomedea, and edwardsii, form distinct clades that are roughly equidistant genetically, with diomedea perhaps closer to edwardsii. Their study of morphology found diomedea and borealis very close, with edwardsii somewhat more distant. I've treated this as an unresolved trichotomy on the tree. Following the recommendations of Sangster et al. (2012), the three Atlantic taxa are considered distinct species. The Mediterranean population takes the name Scopoli's Shearwater, Calonectris diomedea, the Cape Verde population becomes Cape Verde Shearwater, Calonectris edwardsii, while Cory's Shearwater is now restriced to Calonectris borealis.

The Cory's/Scopoli's split is of potential interest in the ABA area as there are several specimens of Scopoli's from New York in the early 20th century (Bull, 1974). More recently, Scopoli's has been photographed off the North Carolina and Florida coasts.

That brings us to the Puffinus species swamp. Although Austin et al. (2004) went a long way toward clarifying matters, not all of their results were conclusive, and an inability to extract DNA from certain specimens meant that some taxa were not included (specimens of auricularis, bannermani, and gunax did not yield usable DNA, while heinrothi was not sampled at all). They only examined a single gene: cytochrome-b. Although cytochrome-b is usually pretty reliable at this level of analysis, we would be happier if it were confirmed by a multi-gene analysis. Moreover, some clades have weak support, and additional genes might clarify the situation there.

Several extinct Puffinus taxa have been identified. Olson (2010) makes a strong osteological case that fossil bones from Bermuda previously named P. parvus actually belong to Boyd's Shearwater, P. boydi. It appears likely it was extirpated from Bermuda following human occupation. Interestingly, Audubon's Shearwater then briefly colonized the island, but was extirpated in the 20th century. Ramirez et al. (2010) attempted to examine DNA from the extinct Lava Shearwater, P. olsoni, and the Dune Shearwater, P. holeae. Although they were successful with with olsoni, which is probably best regarded as a form of the Manx Shearwater, P. puffinus, they were unsuccessful with holeae.

One interesting thing about the various Puffinus races is the limited overlap in breeding range. Only the Manx Shearwater, P. puffinus even shares an island with other types of Puffinus. This happens even when two or more Puffinus are present in the same area. This helps strengthen the case for species status of a number of races.

Heinroth's Shearwater, Puffinus heinrothi, differs in plumage from most of Puffinus (in our narrow sense). No DNA information is available. It's probably relatively basal and I've listed it first to highlight the uncertainty.

Of the taxa we have DNA for, the Christmas (nativitatis) and Galapagos (subalaris) Shearwaters are basal. They may be more closely related to each other than the rest of Puffinus, but this is not entirely clear (compare Austin et al., 2004 and Ramirez et al., 2010). In any event, the remaining species form a clade, with Hutton's (huttoni) and Fluttering (gavia) Shearwaters of New Zealand grouping together. All of these taxa are monotypic.

The rest of the Puffinus shearwaters are more tightly grouped, but divide into two parts: an Audubon/Manx group and a Tropical Shearwater group. However, there is some ambiguity in the analysis, and the Manx group may actually be basal (or two basal groups). In any event, the inferred timing of the split between Manx (puffinus), Yelkouan (yelkouan), and Balearic (mauretanicus) Shearwaters post-dates the refilling of the Mediterranean Sea about 5 million years ago. Further, the split between the Atlantic Manx/Audubon two clades may have been driven by the closing of the Isthmus of Panama which completed about 3 million years ago. If the isthmus hypothesis is correct, I wonder whether there was one widespread small shearwater prior to the cleavage of the oceans, or whether groups separated on either side of the isthmus then diversified east or west into their respective seas, finally meeting again near the Tropic of Capricorn north of New Zealand.

Besides the Manx group, the Atlantic part includes the Little/Audubon's group. The southerly Little Shearwater (assimilis), includes assimilis, tunneyi, kermadecensis, and haurakiensis. The subspecies elegans has been raised to species level as Subantarctic Shearwater. The northerly Audubon's group includes 4 taxa: Audubon's Shearwater (P. lherminieri lherminieri and P. l. loyemilleri (if valid)), Barolo Shearwater (P. baroli, and Boyd's Shearwater, P. boydi.

The last group contains the rest of the shearwaters. Before proceeding, we consider the Townsend's Shearwater complex, which has been studied by Martínez Gómez et al. (2015). They found that auricularis and newelli are not genetically distinct. Accordingly, Newell's Shearwater, Puffinus newelli, is lumped into Townsend's Shearwater, Puffinus auricularis. However, the third subspecies, myrtae, is sufficiently distinct to elevate to a species, Rapa Shearwater, Puffinus myrtae.

The remaining shearwaters breed in the Indian and Pacific Oceans, from the east coast of Africa to the west coast of the Americas. The first portion is relatively clear-cut. It includes the recently discovered Bryan's Shearwater, Puffinus bryani (Pyle et al., 2011), the monotypic Black-vented (P. opisthomlelas), and Townsend's (P. auricularis, including newelli) Shearwaters, and Rapa Shearwater (P. myrtae).

The 10 remaining taxa appear to be closely related. The unsampled Bannerman's Shearwater, P. bannermani, of Japan is treated as a separate species, as is the Persian Shearwater (P. persicus plus temptator). The remaining races are very closely related and are treated as a single species: Tropical Shearwater, P. bailloni. However, this species is sometimes split further into a Pacific group, Atoll Shearwater (dichrous, plus polynesiae, colstoni, nicolae, and presumably gunax), leaving bailloni and the possibly redundant atrodorsalis as Baillon's Shearwater.

CICONIIFORMES Bonaparte, 1854

Although Hackett et al. (2008) found that the storks were basal in the remaining Ardeae (after the penguins and seabirds), Gibb et al. (2013) placed them next to the herons. However, Jarvis et al. (2014) came up with a different arrangement of the taxa, casting doubt on the Gibb et al. treatment. The latest analyses are from Prum et al. (2015) and Kuramoto et al. (2015), who both found the stocks to be basal in this group.

Slikas (1997) did not come to a definitive conclusion on how to arranged the genera of the Ciconiidae. I've adopted her maximum likelihood tree. However, it may not be correct, and there were indications that Ciconia itself may not be monophyletic.

Ciconiidae: Storks Sundevall, 1836

6 genera, 19 species HBW-1

SULIFORMES Sharpe 1891

AOU officially adopted the term Suliformes in the 51st supplement. Sharpe had previously used Sulae as a suborder. For that matter, he also had Fregatae and Phalacrocoraces as suborders. The Suliformes had previously been considered part of the Pelecaniformes, a tradition that dates back to their naming by Sharpe.

The Suliformes were traditionally considered part of the Pelecaniformes (as were the tropicbirds). After all, how likely was it that such unusual features as a totipalmate foot and gular pouch would arise independently? They also share the location of the salt-excreting gland and all lack an incubation patch. These similarities lead Linneaus to put all but the tropicbirds (which lack the gular pouch) in the same genus.

Fregatidae: Frigatebirds Degland & Gerbe, 1867 (1840)

1 genus, 5 species HBW-1

The frigatebird taxonomy follows Kennedy and Spencer (2004).

Sulidae: Gannets, Boobies Reichenbach, 1849 (1836)

3 genera, 10 species HBW-1

Click for Sulidae tree
Click for Sulidae tree

Sulid taxonomy follows Patterson et al. (2011), which is similar to Friesen et al. (2002), except that Papasula is considered basal. The extinct Tasman Booby, often considered a separate species, is here considered a subspecies of the Masked Booby following Christidis and Boles (2008). More recently, Steeves et al. (2010) provides strong evidence for this treatment. They further argue that Sula dactylatra tasmani is identical with the still extant subspecies S. d. fullagari, in which case both should be referred to as S. d. tasmani.

Anhingidae: Anhingas Reichenbach, 1849 (1815)

1 genus, 4 species HBW-1

Phalacrocoracidae: Cormorants Reichenbach, 1849-50 (1836)

3 genera, 42 species HBW-1

The arrangement below is now based primarily on Kennedy and Spencer (2014). Previously, I had used the DNA analyses of Kennedy et al. (2000, 2001, 2009) and the osteological analysis of Siegel-Causey (1988), following Kennedy et al. in case of disagreement. You can click on the tree diagram for the phylogeny. The species in black were included in Kennedy and Spencer, while no DNA data is available for species marked in blue on the tree. In those cases, I've followed Sigel-Causey when possible. The paper by Kennedy et al. (2009) resolved the long-controversial status of the Flightless Cormorant. They found it is sister to the Neotropic and Double-crested Cormorants.

On the tree, I've included some of the available genus names that could be used to subdivide Phalacrocorax. Unless they are generally adopted, they are perhaps mostly best thought of as subgenera. However, the Red-legged Cormorant is so genetically distant and so distinct that I have moved it to Poikilocarbo.

Although work has been done on the phylogeny of the blue-eyed shag complex, the correct species limits remain murky. There are eight Phalacrocorax taxa involved: albiventer, atriceps, georgianus, melanogenis, bransfieldensis, verrucosus, purpurascens, and nivalis. Kennedy and Spencer (2014) found three clades in the group: (1) albiventer, atriceps, and georgianus; (2) melanogenis and bransfieldensis; (3) verrucosus, purpurascens, and nivalis, with clades (2) and (3) closer to each other than to clade (1). The genetic distances are close enough that these allopatric taxa could be considered one species.

Following SACC, the continental representatives of King Cormorant, Phalacrocorax albiventer are considered a color morph of the Imperial Cormorant, Phalacrocorax atriceps (aka Blue-eyed Shag). Rasmussen (1991) makes a strong case for this. The key points are in the abstract: frequent hybridization and non-assortative mating in the contact zones. The genetic distance as measured using allozymes also seems very small.

Kennedy and Spencer (2014) found that the King Cormorants from the Falklands are different from continental `albiventer' (labelled atriceps in the paper, and presumed a color morph). They don't seem to include any of the white-cheeked color morph of atriceps. They found atriceps to be sister to georgianus and the Falklands sample basal to both. Note that Rasmussen's (1991) arguments don't necessarily pertain to the Falklands birds. Because of this I treat the visually distinct King Cormorant of the Falklands as a separate species, Falkland Cormorant, Phalacrocorax albiventer (the type of albiventer is from the Falklands).

Antarctic Shag, Phalacrocorax bransfieldensis, and South Georgia Shag, Phalacrocorax georgianus, are split off as separate species (Siegel-Causey and Lefevre, 1989). They present evidence that the breeding range of the Antarctic Shag formerly included the area around Tierra del Fuego, part of the breeding range of P. atriceps. They argue that there is no sign of interbreeding, indicating they are separate biological species. Kennedy and Spencer (2014) found that the Antarctic Shag is more closely related to the Crozet Shag than the Imperial Cormorant. The South Georgia Shag seems distinct from the Imperial Cormorant, and is arguably also a separate species.

That still leaves 3 taxa to deal with. Unfortunately, there seems to be little solid information to work with. Christidis and Boles (2008) note all this, but consider these three taxa to be subspecies of P. atriceps. There is one piece of evidence. The genetic distance between purpurascens and albiventer is small enough for them to be a single species. However, it's also large enough to be different species. In HBW-1, Orta (1992) takes the opposite tack and splits them.

In version 2.17 I followed Christidis and Boles concerning melanogenis, nivalis, purpurascens. This left me with the same four species as Sibely and Monroe (1990). I gather I'm not the only one uncomfortable with that solution. It just doesn't make biogeographic sense to have birds breeding on the other side of the world lumped into atriceps when the physically closer taxa are considered separate species. In the absence of definitive information, this version follows Orta (1992) in considering them as three species.


Although some analyses have indicated that the herons and ibises are sister clades, support has been weak. Gibb et al. (2013) studied the complete mitochondrial genome of 4 herons, 4 ibises, and related taxa. They found that the herons and ibises do not form a clade, and estimated that they have been separate lineages since the early Paleocene. Since there is uncertainty about their closest relatives, and each represents a truly ancient lineage, I treat them both in their own orders.

Kuramoto et al. (2015) have found evidence of early hybridization between ancient ibises and herons following the split of between the heron and pelican lineages. That would explain the conflicting results in earlier analyses.

Threskiornithidae: Ibises, Spoonbills Poche, 1904

13 genera, 35 species HBW-1

Threskiornithidae tree The traditional treatment of the ibises and spoonbills as sister subfamilies is just wrong. The spoonbills are not the sister group of the ibises. Rather, they are most closely related to Threskiornis and perhaps Pseudibis. Krattinger's MA thesis (2010) shows this fact clearly. Chesser et al. (2010) is consistent with this idea, and it already appeared in Sibley and Ahlquist (1990; esp. Fig. 367). Oddly, Sibley and Ahlquist did not comment on it. Perhaps they found it too unbelievable.

Interestingly, there had been other hints that the spoonbills should not be treated as a subfamily. Matheu and del Hoyo (1992=HBW-1) mention that the Eurasian Spoonbill has been known to hybridize with Black-headed Ibis,Threskiornis melanocephalus. Unfortunately, they did not make the connection with Sibley and Ahlquist's results.

Krattinger (2010) also estimated divergence times. His results suggest that the spoonbill clade originated about 15 million years ago (with large error bars). That time span is more than sufficient to evolve even such a distinctive bill. The Hawaiian Honeycreepers evolved theirs in half that time (Lerner et al, 2011).

Krattinger did find a deep division in Threskiornithidae, but it was between the exclusively New World genera (Eudociminae) and the rest (Threskiornithinae), not between the ibises and spoonbills. The treatment as subfamilies emphasizes this radical change in taxonomy of the ibises and spoonbills.

Krattinger (2010) examined DNA from just over half of Threskiornithidae. The exact position of some of the Old World genera was not conclusively resolved (Bostrychia, Lophotibis, Nipponia), but this tree is a reasonable interpretation of what Krattinger found. The resulting tree is also consistent with Chesser et al. (2010) and Sibley and Ahlquist (1990). Question marks indicate genera that were not sampled. The order within the spoonbills is based on Chesser et al. (2010), which included all of the spoonbills.

Current thinking is that the extinct Reunion Solitaire was actually an ibis! Moreover, it seems to have been closely related to the sacred-ibises (see Mourer-Chauviré et al., 1995). Accordingly, it appears at the head of Threskiornis.

You may think it odd that the family is called Threskiornithidae when Eudociminae is a much older name. The family was once referred to as Ibididae (based on Ibis Cuvier 1816), but the oldest use of the genus Ibis actually refers to the Mycteria storks. Ibididae had to be replaced, and everyone ultimately settled on basing it on Threskiornis, which replaced Cuvier's version of Ibis. Ultimately, the ICZN ruled on this (Opinion 1674) and the family is called Threskiornithidae.

Eudociminae Bonaparte, 1854

Threskiornithinae Poche, 1904


The status of two monotypic families, the Shoebill and the Hamerkop, has been a perennial issue. The analyses of Ericson et al. (2006a) and Hackett et al. (2008) indicate that both are relatives of the pelicans. Indeed, they could all be lumped into the same family. We keep them separate not only because of their uniqueness, but also because the division between them seems to be ancient. Gibb et al. (2013) estimate that the pelican-shoebill split occurred in the early Eocene. According to Prum et al., the Shoebill is more closely related to the Pelicans and the Hamerkop is basal in the Pelicaniformes.

Scopidae: Hamerkop Bonaparte, 1849

1 genus, 1 species HBW-1

Balaenicipitidae: Shoebill Bonaparte, 1853

1 genus, 1 species HBW-1

Pelecanidae: Pelicans Rafinesque 1815

Pelican tree
Pelican species tree

The pelicans have been studied by Kennedy et al. (2013). The arrangement on the tree and order below reflects the relationships they found. Note how the New World Pelicans and Old World Pelicans form sister clades. They also found that the Pink-backed, Dalmatian, and Spot-billed Pelicans are quite closely related.

1 genus, 8 species HBW-1

ARDEIFORMES Wagler, 1830

Ardeidae: Herons, Egrets, Bitterns Leach, 1820

22 genera, 77 species HBW-1

Ardeidae tree The Boat-billed Heron was previously considered to be the only member of the Cochlearidae, but is really just another heron. The list here is pieced together from the limited DNA evidence available (Chang et al., 2003; Huang et al. (2016), Päckert et al. (2014), Sheldon et al., 2000; Zhou et al., 2014, 2016) as well as the barcoding tree Raty posted to BirdForum in 2014. The traditional morphological evidence of McCracken and Sheldon (1998) was also consulted.

Much of the DNA evidence is limited to cyt-b and/or barcodes. Exceptions are Chang (2003), which uses 12S rRNA, and Zhou et al. (2014, 2016), which both use the complete mitochondrial genome. We lack a complete tree with good coverage. As a result, the placement of some taxa remains quite tentative.

Limited DNA evidence puts the Tigriornithinae (tiger-herons) first, followed by the Cochlearinae (Boat-billed Heron). Next are the Botaurinae (bitterns) including Zebrilus, Botaurus and Ixobrychus. Chang et al. (2003), Päckert et al. (2014), and Zhou et al. (2014, 2016) found the Black Bittern embedded in Ixobrychus. It's sometimes put in a monotypic genus Dupetor, which is here considered part of Ixobrychus.

All but three of the Botaurinae were considered by Päckert et al. (2014). The linear order here is based on their results, except that they found the Least Bittern, Ixobrychus exilis, closer to Botaurus than to the other Ixobrychus. They looked at the barcoding region and part of cytochrome-b. The barcoding results were a bit strange. The cyt-b + barcoding phylogeny (Figure 3) was much more reasonable. Both suggest moving the Least Bittern to Botaurus, which I have done. Even though they look similar, it's not surprising that the Least Bittern is not sister to the Little Bittern group (I. minutus–novaezelandiae). The osteological evidence in McCracken and Sheldon (1998) had long ago indicated it is not as close to the Little Bittern group as one might think.

It's not at all clear what happens with the night-herons. There's some evidence that they are a clade, but that is incomplete and has only weak genetic support. The cytochrome-b analysis of Sheldon et al. (2000) was ambiguous about whether Nycticorax and Nyctanassa form a clade, but Chang (2003) found them in a clade using 12S rRNA. Zhou et al. (2016) grouped Nycticorax with Gorsachius. Zhou et al. also found that White-eared Night-Heron was closer to Egretta. I've transferred it to the monotypic genus Oroanassa (Peters 1930). There is also uncertainty about the affinities of the White-backed Night-Heron. It has been variously placed in Nycticorax and Gorsachius, or in its own genus Calherodius (sometimes with the White-eared Night-Heron). McCracken and Sheldon (1998) did not find them to be sisters. For now, I'm putting the White-backed Night-Heron in a monotypic Calherodius (Bonaparte 1855) and leaving it in the night-heron subfamily, Nycticoracinae.

The remaining genera seem to be more closely related to each other than to anything else, and are placed in subfamily Ardeinae. They appear to fall into two main clades.

The first clade includes the endangered White-eared Night-Heron, Oroanassa magnifica, together with Pilherodius, Syrigma, and Egretta. I've ordered Egretta to conform with available genetic data.

Based on the Zhou et al. (2016), which uses the complete mitochondrial genome, the other clade consists of two parts. The first includes Butorides and Ardeola. Barcoding data suggests that Agamia is sister to Ardeola. Interestingly, barcoding data also suggests that the South American and Old World Striated Herons are sister taxa, with the Green Heron a more distant relative.

The remaining herons and egrets are in the Bubulcus-Ardea clade.

We consider the Ardea clade first. The Great Egrets are put in a separate genus, Casmerodius. The 12S rRNA tree of Chang et al. puts them sister to the Intermediate Egret, and both sister to Ardea (or Ardea+Bubulcus). Sheldon et al. (2000) didn't include the Intermediate Egrets (Mesophoyx), but also found Casmerodius sister to Ardea. These were formerly placed in Egretta, but the DNA says no on this. Some authors put them all in Ardea.

The placement of Bubulcus follows Chang et al., (2003) Sheldon et al. (2000), and Zhou et al. (2014, 2016). The last two are based on the complete mitochondrial genome. Zhou et al. actually suggest merging Bubulcus, Casmerodius, Mesophoyx, into Ardea. However, these are both distinctive and genetically distant from the main Ardea group and better maintained as separate genera.

Splits and Potential Splits

The Cattle Egret, Bubulcus ibis, has been split into Western Cattle Egret, Bubulcus ibis, and Eastern Cattle Egret, Bubulcus coromandus based on differences in plumage and DNA (Raty barcode tree).

The Intermediate Egret, Mesophoyx intermedia, has been split into Intermediate Egret, Mesophoyx intermedia, Yellow-billed Egret, Mesophoyx brachyrhyncha (sub-Saharan Africa), and Plumed Egret, Mesophoyx plumifera (Australasia) based on differences in breeding plumage (HBW/BirdLife).

Kushlan and Hancock (2005) and Christidis and Boles (2008) suggested treating the Great Egret as two species: Casmerodius albus and Casmerodius modestus. Certainly, the genetic distance between some of the Great Egret subspecies is quite large, comparable to that between Great and Intermediate Egret (Sheldon, 1987), but the subspecies analyzed are egretta and modestus. This suggest no significant gene flow between egretta and modestus, that they are distinct biological species. But how do the other subspecies (albus and melanorhynchos) fit in? Both Kushlan and Hancock, and Cristidis and Boles, suggest that egretta should be grouped with albus and melanorhynchos. However, Pratt (2011) argues that the split should be between egretta and the rest, mainly on the basis of breeding plumage. However, Raty's 2014 barcoding tree suggests that albus and egretta are more closely related to each other than to modestus (with low support). It also suggests a species level difference between albus and egretta. Further, all 4 subspecies (including melanorhynchos) have distinctive breeding plumages.

Accordingly, the Great Egret, Casmerodius modestus, has been split into Eastern Great Egret, Casmerodius modestus, Great White Egret, Casmerodius albus African Great Egret, Casmerodius melanorhynchos, and American Egret, Casmerodius egretta, based on differences in breeding plumage and except for melanorhynchos, DNA. The order is based on the assumption that the Eastern Great Egret is basal in the group.

The status of the Great White Heron, Ardea herodias occidentalis, remains controversial (e.g., Stevenson and Anderson, 1994). It is very near the borderline for species status. Genetically, it is nested within the larger Great Blue Heron clade. However, in their overlap zone in extreme south Florida, there seems to be little interbreeding between the dimorphic Great White Herons (the dark morph is sometimes called Würdemann's Heron) and the monomorphic Great Blue Herons (McGuire, 2002). Moreover, the Great Blue Herons of the Florida peninsula (wardii) are more closely related to those of the northern US (herodias) than to occidentalis. However wardii and herodias are closer to occidentalis than any of them are to fannini. For the present, I'm following AOU by treating them as one species although I'm not convinced this is correct.

Tigriornithinae: Tiger-Herons Bock, 1956

Cochleariinae: Boat-billed Heron Chenu and des Murs, 1854 (1838)

Botaurinae: Bitterns Reichenbach, 1849-50

Nycticoracinae: Night-Herons Bonaparte, 1854

Ardeinae: Egrets and Herons Leach, 1820

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