Proposal (77) to South American Classification Committee
Split Threnetes leucurus from Threnetes niger
Background: Threnetes
leucurus (Pale-tailed Barbthroat) with a range through most of
Amazonia, has been long considered a separate species from Threnetes
niger (Sooty Barbthroat), found in French Guiana and adjacent Brazil
(Amapá). Grantsau (1969) described a new species in this complex, Threnetes
loehkeni from Amapá. Hinkelmann (1988) suggested that Threnetes loehkeni
is best treated as a subspecies of leucurus, but at that
time did not include Threnetes niger in the mix. In this paper, he also
nixes a couple of Ruschi taxa (Threnetes cristinae and T. niger freiri described from specimens from Amapá. In HBW,
Hinkelmann (1999) lumped all of the Amazonian Threnetes into one species
under the oldest name niger. He stated "niger represents
a melanistic form of geographically limited distribution, based on apomorphic
characters within the range of variation found in leucurus; otherwise
the two are apparently inseparable." Because of Hinkelmann's uncertainty
about Threnetes niger and the fact that Hinkelmann and Schuchmann (1997)
did not correctly apply the names in this case, the taxonomic
issues did not really become generally appreciated until the publication of
HBW, Vol. 5.
Analysis:
The taxon niger is as Hinkelmann states a melanistic bird. I
have seen two specimens, one at the Field Museum, and one in Sao Paulo. On these
specimens, the basic Threnetes plumage pattern is visible
underlying the dark coloration of the underparts. The basic plumage pattern is
that of loehkeni. This led Parker et al (1996) to suggest
that loehkeni was probably a pale morph of niger. The
logic of Hinkelmann's treatment of loehkeni and leucurus as
conspecific with niger, is not made explicit, but seems to be based on loehkeni
as a subspecies of leucurus and niger being a melanistic
population allied to one or the other of these (see Hinkelmann and Schuchmann
1997 for the most explicit discussion, although they mess up the name there).
It looks to
me like Hinkelmann is correct that niger and loehkeni are
basically melanistic and normal morphs of the same thing. It isn't completely
clear that whether there is a geographical element to this, so that they should
be considered two subspecies, or whether they are morphs within the same
subspecies. In HBW, Hinkelmann takes the former view. In Hinkelmann and
Schuchmann (1997) they suggest that the latter view is more likely. The
question is whether the treatment of niger plus loehkeni as
conspecific with the widespread leucurus is appropriate. Hinkelmann
(1988) suggests that the plumage characters that Grantsau (1969) mentions for loehkeni
are invalid, except for the tail pattern. In loehkeni (and in niger),
the tail is dark green, with very narrow pale tips to the outer four rectrices
on each side. In leucurus, the outer four tail features are mostly pale
(ranging from white to ochraceous depending on the subspecies), with a black
subterminal band followed by pale tips. The pale on the tail is broadest on the
innermost of the four outer feathers, so nearly completely pale, and gets
progressively blacker as you move outward, so that the outermost feather is
about 50% black. The result is a very different and distinctive tail pattern
from that of niger and loehkeni (the plate in HBW does a
good job on these birds).
Hinkelmann
(1988) treated loehkeni as a "distinctive subspecies" of leucurus,
stating "the colouration of loehkeni does not go beyond the variation
found in all subspecies of T. leucurus, variation which is probably due
to age and sex." I would agree with Hinkelmann on this, except for the
tail pattern. Although females and young birds of leucurus have less
white in their tails than do adult males, in the 100 +/- specimens of leucurus at
the Field Museum, none approach the condition of loehkeni.
Whether to
treat niger as a distinct species from leucurus or as
conspecific is difficult, however, I think that recognizing two species is the
best course. The two taxa approach one another moderately closely, and may
occur together. Typical leucurus occurs in Surinam and southern
Amapá, at least (Hinkelmann 1988). Tostain et al. (1992) listed both species
from French Guiana, and gave both from two localities, St. Georges and Saul.
However, since they do not give subspecies, I don't know whether the leucurus may
refer to loehkeni rather than nominate. As an aside I would note that
the range of niger within French Guiana includes most of the border
with Surinam, so it should occur in Surinam, but I am unaware of any records.
Given the
close approach of niger and leucurus and the possibility of
sympatry without any indication of intermediate tail-patterned birds being
found, and the lack of any reports of melanistic birds in leucurus from
near the range of niger, I would argue that there is no evidence of
intergradation occurring between niger and leucurus. Further, the
other species in the genus, Threnetes ruckeri, allopatric to these birds
in Trans-Andean forests, is very similar to leucurus in plumage,
except for its distinctive tail pattern. The tail pattern of niger is
even more distinctive than that of ruckeri in my view.
Proposed
change: Recognize Threnetes leucurus as a distinct
species from Threnetes niger, treating loehkeni as
a subspecies of niger. The English name Pale-tailed Barbthroat
would apply to leucurus. Threnetes niger has been called
Sooty Barbthroat, except when treated as conspecific with leucurus. This
name is not particularly appropriate when loehkeni is lumped into
it. Loehken's Barbthroat seems inappropriate as well. Maybe Dark-tailed
Barbthroat?
Recommendation: I
recommend treating Threnetes niger as a distinct species from Threnetes
leucurus, treating loehkeni as a subspecies of niger.
References:
Grantsau,
R. 1969. Uma nova espécie de Threnetes (Aves,
Trochilidae). Papeis Avulsos Zool. 22:245-247.
Hinkelmann,
C. 1988. Comments on recently described new species of hermit hummingbirds.
BBOC 108:159-169.
Hinkelmann,
C. 1999. Pale-tailed Barbthroat (Threnetes niger) [species account], in del
Hoyo, J., Elliot, A. & J. Sargatal, eds. Handbook of the Birds of the
World. Vol. 5. Page 539.
[How should you cite species accounts in this?]
Hinkelmann,
C. and K. Schuchmann. 1997. Phylogeny of the hermit hummingbirds (Trochilidae:
Phaethornithinae). Studies on Neotropical Fauna and Environments 32:142-163.
Parker, T.
A., III, D.F. Stotz, and J. W. Fitzpatrick. 1996. Ecological and Distributional
Databases, in Stotz, D. F., J. W. Fitzpatrick, T. A. Parker
III, and D. K. Moskovits, Neotropical Birds: Ecology and Conservation.
University of Chicago, Chicago.
Tostain,
O., J.-L. Dujardin, Ch. Erard, and J.-M Thiollay. Oiseaux de Guyane. Société d'Etudes Ornithologiques, Brunoy,
France.
Doug Stotz, November 2003
________________________________________________________________________________________
Comments
from Robbins: "[YES.] Doug has done a good job of providing details
to the convoluted treatment of the T. niger complex."
Comments
from Stiles: "NO. Sounds reasonable but lacks solid published evidence -
if Doug were to publish something on this, I would probably go for it."
Comments
from Zimmer: "A reluctant "NO". I think Doug's arguments are
persuasive, but once again, I think there needs to be some published analysis,
particularly since the historical treatments have been so muddled."
Comments
from Jaramillo: "YES, although reluctantly. A quick note stating what has
been stated here with illustrations of tail pattern and a map would be highly
encouraged."
Comments
from Nores: "YES. Acepto
reconocer a Threnetes leucurus como una especie distinta de Threnetes
niger y tratar a loehkeni como una subespecie de niger.
Pienso que el patrón de la cola de leucurus es concluyente."
Comments
from Remsen: "YES. In retrospect, and after reading the information
assembled by Doug, it seems premature in my opinion to consider leucurus
and niger conspecific -- the burden-of-proof in this case falls on the
treatment that would consider them conspecific."