Proposal (271) to South American Classification Committee

 

Separate Pelecanus thagus from P. occidentalis

 

Effect on South American CL: This would add Pelecanus thagus, Peruvian Pelican, as a species different from Pelecanus occidentalis, Brown Pelican.

 

Background: The last review of the Brown Pelican is Wetmore's (1945) paper, in which he described two new subspecies. These are urinator (Galapagos), and murphyi (Pacific Colombia and Ecuador), two new taxa that pertain to our region. He did not split thagus, but went into considerable detail as to how it differs, and clearly was on the side of splitting it, but feels that he has incomplete information to do so (see below for his direct quote).

 

I am not certain when thagus (Molina, 1782) was included as part of occidentalis, but in recent years some have considered it a separate species, although most of these have been Field Guide authors (Ridgely and Greenfield's Birds of Ecuador, Jaramillo et al. Birds of Chile, etc.). However there has not been any published logic on why it should or should not be part of occidentalis as far as I am aware. There has also not been much attention paid to the fact that the non-breeding distributions of both murphyi and thagus broadly overlap breeding areas of the other taxon, yet no hybridization is known.

 

Analysis and Proposal: The pelicans as a group are well accepted, although the relationship between them and the Shoebill has been suggested to be close, although this has not been resolved. All pelicans are classified in the genus Pelecanus, although the Brown Pelican differs from classic Pelecanus in many ways (marine, plunge-diving behavior, dark plumage etc.); a subgenus, Leptopelicano has been applied to the Brown Pelican.

 

The Brown Pelican separates into three groups. One is thagus in the Humboldt Current region. Large size and various other soft part and plumage features (see below) set it apart from the others. There is californicus, on the Pacific Coast of Baja California etc.; it is larger than the occidentalis group, has a darker brown hindneck stripe, and most importantly develops a red base to the gular pouch during breeding. Finally, the occidentalis group is found on the Atlantic and Pacific, the classic Brown Pelican, smaller with a nice caramel brown hindneck stripe and a yellowish color on the gular pouch during breeding. Biogeographically it may seem like a jumble to have one form in both oceans, and then these larger isolates in the north and south end of the Pacific. However, the pattern clarifies when you look at water temperature. The form occidentalis is associated with warmer waters, whereas californicus and thagus are cold-water taxa. As is often the case with marine birds, water temperature creates the major biogeographical patterns, and is likely what is maintaining them as separate entities.

 

Wetmore (1945) classified various subspecies of the Brown Pelican based on differences in size, soft part colors in breeding adults, and darkness of the hindneck stripe on breeders. The two taxa of relevance to this situation are thagus, which breeds from northern (or is it central?) Peru south to central Chile (Isla Mocha); and murphyi from Pacific Colombia, and Ecuador (southernmost breeding locality being Isla Santa Clara in the Gulf of Guayaquil) (Ridgely and Greenfield 2001). The gap between the southernmost murphyi and northernmost thagus is not huge. They are broadly sympatric during the non-breeding season, and Ridgely and Greenfield (2001) noted a large non-breeding flock of subadult thagus at Isla Santa Clara, one of the breeding localities of murphyi. Similarly, murphyi is regular south to northern Chile (Jaramillo pers. obs.), and it is likely overlooked in many coastal pelican concentrations throughout Peru. Given the broad overlap in distribution, and the fact that these pelicans may breed throughout the year, it is interesting that there are no specimens or reports published of any intermediate birds. There is no evidence of hybridization whatsoever.

 

One of the differences between thagus and murphyi, and from all other "Brown" Pelicans, is its large size. At the end of this account I have copied the size data from Wetmore (1945), which show the substantially larger size of thagus. Because these are linear measurements, the true magnitude of the difference is not apparent. Below is an excerpt from the BNA account (Shields 2002) of Brown Pelican detailing mass:

 

 

"Males 15-20% heavier than females. Mean mass of adult P. o. carolinensis from Florida: male: 3,290 g ± 509 SD (range 2,380-4,040, n = 13); female: 2,824 g ± 677 SD (range 1,830-3,990, n = 13; Schreiber et al. 1989). Individual male and female Peruvian Pelicans weighed 7,030 g and 5,055 g, respectively (Murphy 1936)."

 

In fact, compared to carolinensis (similar in size to murphyi), thagus weighs roughly twice as much! That is a heck of a difference, and immediately obvious in the field. The size difference is enough that even the mechanics of successful interbreeding are likely difficult.

 

In addition to the huge size difference, thagus has a different plumage than other Brown Pelicans. As adults they show extensive pale (whitish gray) scapulars, and upperwings that contrast with a dark brown patch on the inner wing (humerals). Furthermore each feather on the underparts is streaked with pale, giving the body a more ornate, pale streaked look. The pale crest is very long, and looks like a long tuft on many thagus, and the neck stripe is blackish rather than brown. The facial skin is blackish, with restricted pink around the eye, much less pink than in the occidentalis group. On average the extent of reddish on the bill tip is much greater on thagus than other Brown Pelicans, usually extending to half of the bill length, not just restricted to the tip. The bill base is brighter, more yellowish rather than dull horn. But most importantly, thagus has an extensive bright blue striped gular pouch, quite unlike that of the occidentalis group, or californicus, and this blue color is retained for much of the year in adults, although brighter during breeding. In the loral area, thagus develops little black bumps (papillae) unlike any other Brown Pelican, and also the base of the culmen often shows reddish caruncles. The end product of bill, pouch, facial skin, and tuft size gives thagus a radically different look during breeding, than any other Brown Pelican. This in addition to the large size sets it apart. 

 

All of this was not lost on Wetmore (1945), who ended his paper with: "The markedly larger size, the caruncles on the bill in the adult, and the brighter coloration of the bare skin of the head and pouch are so different from what is found in other Brown Pelicans that it may develop with complete information that thagus should stand as a species."

 

Thinking of the white pelicans as a group, the various different species differ subtly, mainly in facial or soft part features which develop in the breeding season, or differences in extent of dark on the wings or upperparts. If thagus was a "white pelican," then the various differences it shows in plumage and breeding display colors (presumably important in pair formation!) would be equivalent to differences seen in currently accepted white pelican species. The size difference alone (it is twice the size) is remarkable, and if you want to see photos of the two species side by side, here is an example: http://www.birdsofchile.com/updates.htm. 

 

Ecologically, thagus is common well offshore, being more pelagic than occidentalis. It also does little plunge-diving; it scoops up fish from the surface or makes shallow dives as opposed to the more spectacular dives of the smaller occidentalis group. Again perhaps due to its size, thagus tends to roost on cliffs, rocks, islands, or other stable surfaces, and it does not tend to roost in trees as does occidentalis.

 

This proposal is odd in that it is not based on any new data, but largely asks to assess bits and pieces available in the literature to change the status of this pelican.  P. o. thagus is a subspecies of occidentalis currently, but really there has not been any reasoning for why this is the correct ranking of this taxon. I realize that one could say this of many taxa in the Neotropics, but this is one where we have huge overlap in distribution (thagus ranges north to central Ecuador, and murphyi as far south as northern Chile) and no evidence of hybridization. 

 

Recommendation: I suggest a YES vote to separate thagus from occidentalis

 

References:

Ridgely, R.S. and P. J. Greenfield 2001. The Birds of Ecuador. Cornell University Press, Ithaca.

 

Shields, M. 2002. Brown Pelican (Pelecanus occidentalis). In The Birds of North America, No. 609 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.

 

Wetmore, A. 1945. A review of the forms of the Brown Pelican. Auk 62: 577-586.

 

 

Appendix 1. Linear measurements (mm) of museum specimens of Brown Pelicans from various locations. Data presented as mean (range, n). From Wetmore 1945.

 

Subspecies/location Wing length Culmen length Tail length Tarsus length

 

P. o. murphyi 

Ecuador, Colombia 

Male 513 (505-526, 11) 328 (310-346, 11) 135 (127-162, 11) 77 (69-81, 11)

Female 485 (478-494, 8) 293 (289-297, 8) 139 (123-175, 8) 71 (61-76, 8)

 

P. o. urinator 

Galapagos Is. 

Male 561 (552-570, 9) 361 (340-379, 9) 140 (130-148, 9) 85 (82 89, 9)

Female 527 (516-546, 5) 329 (307-372, 5) 137 (129-145, 5) 80 (77-85, 5)

 

P. o. thagus 

Peru, Chile 

Male 606 (575-625, 6) 397 (340-425, 6) 152 (140-177, 6) 106 (95-113, 6)

Female 576 (520-606, 14) 354 (332-390, 14) 146 (135-174, 14) 100 (87-107, 14)

 

Alvaro Jaramillo, May 2007

 

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Comments from Remsen: "YES. Placed in the comparative framework of species limits in current classification of Pelecanus, Alvaro's synopsis places burden on those who would continue to rank thagus as a subspecies, in my opinion. With major differences in body size, bare parts coloration, and plumage, thagus seems to differ as much from occidentalis as some of the white pelicans do from one another."

 

Comments from Stiles: "YES. Differences between thagus and occidentalis are of similar magnitude to those between various other currently recognized pelican species. Also it would appear that the opportunity to hybridize exists but this has never occurred, a persuasive point to me."

 

Comments from Cadena: "YES. Morphologically, thagus clearly stands out as different, and I agree that the lack of hybridization despite apparent opportunities is a persuasive point. I wonder, however, whether these birds truly overlap in space at times where interbreeding might be possible (Alvaro only mentioned sympatry of non-breeding individuals). If they only overlap when there is no reproduction going on, the argument does not seem as solid, and the situation would not seem to differ much from that of species that have migratory and sedentary populations that come together during part of the year when they are not breeding (e.g. Tyrannus melancholicus in Amazonia)."

 

Comments from Robbins: "YES. As Thomas, Van, and Gary have correctly pointed out, the morphological differences between thagus and occidentalis are as great or greater than that between the white pelicans that are recognized as species."

 

Comments from Manuel Mar’n A.: "The proposal indicates that in recent years some have treated them as separate species.  In Chile, they have always been treated as separate species.  Chilean and Peruvians (all?) never treated as thagus as a subspecies of occidentalis.

 

"Peters 1931 was the first to place thagus under occidentalis. Hellmayr (1932, Birds of Chile) under thagus wrote " The Brown Pelican of North America is probably conspecific." Hellmayr (1948, Birds of The Americas- 13, part 1 No 2) classified thagus as subspecies of occidentalis, and added a note " it is clearly a geographical representative of the Brown Pelican".  Peters 1979 (second edition vol 1) classified it as P. occidentalis thagus.

 

"Murphy (1936, Oceanic birds; Vol II: 809] under P. o. thagus gave measurements smaller than on those on the proposal. Measurements in Blake (1977, Manual of Neotropical Birds) under occidentalis thagus are exactly the same as the ones given by in the proposal - are those of Blake or Wetmore?

 

"P. [o] thagus certainly differs in size, soft part colors (culmen (ad breeding) pouch and bare skin around the eye) from other subspecies, but it seems that all subspecies differ in soft part colors and size to some degree, e. g., P. o. carolinensis and P. o. californicus. For plumage differences see Schreiber et al. (1989, Plumages and molt of Brown Pelicans, Contributions in Science No 402, Nat. Hist. Museum of Los Angeles Co.)

 

"The place to look for potential hybridization would be northern Peru, but most likely nobody has being looking. They do have a very complex plumage sequence (see Schreiber et al.).  Murphy (1936; 810) indicated that 'all examples seen by him between Costa Rica and Point Pari–as in (northern) Peru agree well with examples from Florida and Gulf of Mexico'."

 

Comments from Pacheco: "YES. Voto em favor da proposi¨‹o, especialmente porque as diferen¨as entre thagus e occidentalis s‹o equivalentes ou maiores que aquelas encontradas entre outros pares de espˇcies de pelicanos."

 

Comments from Zimmer: "YES. Along with the obvious morphological differences, the ecological differences as noted by Alvaro would argue for the split. In addition to the huge size disparity, one can't help but think that differences in facial/gular skin coloration during the breeding season would be important isolating mechanisms even if the two forms were spatially and temporally in a position to interbreed."

 

Comments from Nores: "SI, aunque no totalmente convencido. Lo del tama–o es relativo; Rollandia rolland rolland, por ejemplo, es considerablemente m‡s grande (33-36 cm) que R. r. chilensis (23 cm)Sin embargo, son consideradas s—lo subespecies. Tambiˇn, como se–alado por Cadena, el hecho que superponen su distribuci—n s—lo en ˇpoca no-reproductiva, no constituye un elemento muy s—lido para separarlos."