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
_______________________________________________________________________________________________
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 Marín 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 Pariñas in (northern) Peru
agree well with examples from Florida and Gulf of Mexico'."
Comments from Pacheco: "YES. Voto em favor da proposição, especialmente porque as
diferenças entre thagus e occidentalis são
equivalentes ou maiores que aquelas encontradas entre outros pares de espécies
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 tamaño es relativo; Rollandia
rolland rolland, por ejemplo, es considerablemente más grande (33-36 cm)
que R. r. chilensis (23 cm). Sin embargo, son
consideradas sólo subespecies. También, como señalado por Cadena, el hecho que
superponen su distribución sólo en época no-reproductiva, no constituye un
elemento muy sólido para separarlos."