Proposal
(261) to South American Classification Committee
Proposal 261a. Split Dysithamnus plumbeus and D.
leucostictus
Proposal 261b: Split Dysithamnus tucuyensis from D. plumbeus
or D. leucostictus
Proposals: These proposals are (i) to recognise a split
reflected in almost all recent field guide literature; (ii) for completeness,
to consider a split that has recently been proposed; and (iii) to adopt one of
two possible names for one of the "new" species that would result.
Like the recent Conopias proposal, no formal analysis directly on topic
has ever been presented in a scientific journal. However, the first split is
strongly supported by morphological, biogeographical and vocal evidence that
has been published in various field guides and CDs. The second split is
apparently supported by vocal and biogeographical considerations but less
published literature exists on the topic and the differences are not as clear-cut
as on the first.
Distributions:
Plumbeous Antvireo D. plumbeus is a lowland Atlantic
forest species endemic to Brazil, with a small and fragmented range. It is
currently assessed as Vulnerable by BirdLife International (2004). This is of
note given BirdLife's move towards convergence with SACC.
Nominate White-streaked or White-spotted Antvireo D. [p.]
leucostictus is present in cloud forest on the east slope of the Andes from
Peru to Colombia.
Greater D. leucostictus and D. plumbeus have
disjunct ranges c. 4000 km apart. Any recent contact is unlikely. The
possibility that variations in morphology and voice from localities of sound
recordings or specimens (discussed below) could vary clinally in the
intervening regions can be discarded.
Venezuelan Antvireo D. [l./p.] tucuyensis is
present in the coastal cordillera of Venezuela and has recently been assigned
species rank in a major field guide on the basis of its voice and plumage
(Hilty 2003) following previous suggestions that this might be warranted
(Ridgely & Tudor 1994; Zimmer & Isler 2003). The taxon has an
apparently disjunct range, with records of D. leucostictus only
in the Amazonian-bordering region of the east slope of the Andes north to in
Meta, Colombia (recent range extensions set out in Salaman et al. 2002) and no
records of any relative in Norte de Santander, Tamá or Merida regions. D.
leucostictus is a forest specialist that is not abundant where found and
has a narrow elevational range. The apparent gap in records from Meta to Norte
de Santander in Colombia may not be a real one given the lack of mist-netting
or other studies in that region (and I have heard of an unpublished sight
record in Santander). The lack of any records in the Merida mountains may be
more significant.
Morphology:
D. plumbeus and greater D. leucostictus are
similar in male plumage, though may differ slightly in the extent of white
barring on the wings and shade of black/very dark grey on the underparts. The
females, however, look nothing like one another. Female D. plumbeus
are uniform plain brown with 2 whitish wingbars and a lighter throat.
Female D. leucostictus have slate grey underparts with broad white
streaking and a chestnut mantle, wings and crown.
The plumage differences between D. plumbeus and
greater D. leucostictus have been discussed in at least two
publications: Ridgely & Tudor (1994) in Birds of South America:
Suboscines and Zimmer & Isler (2003) in Handbook of the
Birds of the World. In the latter case, plumages are illustrated.
Turning to D. [l./p.] tucuyensis, males are similar to
nominate D. leucostictus. In females, the streaking on the underparts is
broader and less contrasty (see plates in Zimmer & Isler 2003 and Hilty
2003).
Voice:
Loudsongs of the all three taxa have been published in commercially
available recordings and have been described and discussed in at least two
publications (Ridgely & Tudor 1994 & Zimmer & Isler 2003). A
sonogram of D. leucostictus' call is set out in Whitney (1992).
Quoting Zimmer & Isler (2003):
"D. plumbeus: short (4 notes, 1.3 s) series of
moderately long whistles (notes longer than spaces between notes), second note
at higher pitch than first, 3rd and 4th declining in pitch, first and second
notes less intense.
"D. leucostictus: short (6 notes, 1.8 s) easily
countable series of strong whistles, pitch falling (except sometimes initial
note), first and last notes more intense.
"D. [l./p.] tucuyensis: moderately long (13
notes, 2.7 s) barely countable series of strong whistles, pitch and intensity gradually
rising to middle notes, then gradually declining."
English Names (to be considered in separate proposal if one or
both of the splits accepted:
Two possible English names exist for D. leucostictus. The
historic name is "White-spotted Antvireo" (referred to in e.g. Meyer
de Schauensee publications, pre-split). However, Ridgely & Tudor (1994)
noted that the female's underparts are streaked, not spotted. They suggested
"White-streaked" instead. "White-streaked Antvireo" is
probably more widely used in works referred to herein. Some exceptions are Sibley
& Monroe (1993) and BirdLife International (2004), who each go for
"White-spotted". A Google straw poll also showing 225-98 in favour of
"streaked". Given that historical stability arguments are of little
relevance for a taxon recently recognised as a species, I recommend
"White-streaked" as the better name of the two names.
Both Ridgely & Tudor (1994) and Hilty (2003) suggested
"Venezuelan Antvireo" for a split D. tucuyensis, thus
with only one name, no proposal is raised on this issue.
Conclusions:
Ridgely & Tudor (1994) concluded that D. leucostictus and
D. plumbeus should be split as a result of their "wide range
disjunction, very different elevations, strikingly different female plumages
and very different behaviour and songs". Zimmer & Isler (2003) agreed
and the split has also been followed by subsequent BirdLife International
publications (various), checklists of Northern South America (Rodner et al.
2000) and Colombia (Salaman et al. 2001), Birds of Ecuador (Ridgely &
Greenfield 2001) and a recent range extensions article (Salaman et al. 2002)
among others. This split is strongly supported and widely followed.
Evidence for the D. tucuyensis split is less
strong than that for the D. leucostictus split. Only Hilty (2003)
among recent field guide publications recognises this split, with other
publications (e.g. Ridgely & Tudor 1994, Zimmer & Isler 2003) merely
noting that it requires further investigation. Having observed and heard both
taxa in the field, I suspect Hilty is right. The only question is whether this
is one of those splits that the SACC decides it would like to see more evidence
on before accepting.
Conservation Implications: A split D. leucostictus renders
D. plumbeus Vulnerable. This is one of very few taxonomic treatments
where BirdLife International (who recognise the split) has not followed SACC. A
split D. tucuyensis would require re-evaluation of each of the other two
taxa, both of which have rather small ranges and are largely restricted to
forest. Without putting a conservation cart before a taxonomy horse, I note
merely that these proposals could have important conservation ramifications.
Recommendations:
1. Split D. leucostictus: YES, definitely.
2. Split D. tucuyensis: tentatively in favour based on
field experience, published sound recordings and descriptions thereof, but
committee members may consider that a more detailed study (involving e.g.
biometrics, molecular work) may be prudent before making a change. Yes is to
accept the split; no to reject it.
References:
All on SACC references site.
Thomas
Donegan, January 2007
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Comments from Zimmer: "A qualified "NO".
I think there is no question that D. plumbeus is specifically
distinct from the other two forms, regardless of the species concept employed.
Vocal and morphological differences, combined with a humongous range
disjunction all point to plumbeus as being a separate beast, and
indeed, that is how Mort Isler and I treated it in HBW Volume 8. Conservation
considerations (as suggested by Thomas Donegan) also argue for this change
being made sooner rather than later, since plumbeus is clearly a rare
and threatened bird. So, I could go along with that split (261a). However, the
case for splitting leucostictus and tucuyensis from one another
is much less clear-cut, and really does require a thorough, quantitative
analysis. Such an analysis is not only under way, but is well-under way (Isler
& Isler et al.), and should be completed and submitted for publication
soon. I would suggest that we hold off on this proposal until this analysis is
completed. In the case of plumbeus, the analysis will confirm what
has long been suspected; in the case of leucostictus and tucuyensis,
it is really required to be certain of which way to go."
Comments from Remsen: NO. With the formal analysis
indicated by Kevin underway, let's wait."
Comments from Stiles: (261a) "YES. The evidence
favoring the split of leucostictus from plumbeus is much stronger
than that for continuing to lump them, despite the lack of a specific quantitative
analysis. A) the huge range disjunction is matched by several other taxa now
(if not always) split, like Baryphthengus, B) the vocal evidence is
quite convincing - at least they certainly sound different to me, and C) the
phenomenon of heterogyny (females much more different than males) occurs in
several other thamnophiline genera, notably Cercomacra - in the
latter, some of the species involved are sympatric. These two were split by
Chapman (1926) on the basis of the different females, but he noted the great
similarity of the males, which apparently was the criterion used by Hellmayr to
lump them; in this case, I prefer to follow Chapman. I also agree with
"White-streaked" as an English name."
Comments from Stiles: 261b. "NO, for now. The differences
in female plumages are much less pronounced, the voices are less different (but
certainly not alike) - here a more detailed study would be nice."
Comments from Nores: (261a) "YES. Pienso que hay sobradas razones para considerarlos
especies distintas. El plumaje de la hembra y el canto son importantes y el
gran gap entre los rangos es para mí definitivo. No puedo pensar que una
"understory species" pueda tener una subespecies separada 4000 km."
Comments from Nores: (261b) "NO. Aunque el caso es algo parecido al anterior, las
diferencias morfológicas y la aislación de los rangos no son tan marcados. De
todos modos, sería importante ver si las diferencias en los cantos indicada por
Donegan son suficiente para considerarlas especies distintas."
Comments from Cadena: "261a, 261b. NO for now. The
relevant data have not been published, but they will be soon. Let's wait for
the publication of the analyses described by Kevin."
Comments from Robbins: "NO, for reasons outlined by
Kevin, it seems prudent to hold off on making any changes at the moment given
that a manuscript is eminent."
Additional comments from Stiles: "As per Daniel's
comment - I am willing to change my vote to a temporary "no" if a
manuscript on these birds is indeed in the works and could be at least accepted
by the time we go to print."
Additional comments from
Donegan: "I was unaware of the forthcoming
publication mentioned by Kevin Zimmer above. However, I do not think that this
changes anything as regards proposal "a". Few, if any, authors other
than SACC treat D. leucostictus and D. plumbeus as lumped. As Gary Stiles
has pointed out, the split/lump status of these species has been debated for
the best part of 80 years and has been resolved in the last 15 or so with vocal
and biogeographical evidence in favour of the split. Giving the SACC current
treatment for this/these species some kind of "holy cow" status seems
strange when it is by far the exception to all other recent ornithological
literature. Further, we have a strong indication that a forthcoming article
will "confirm what has long been suspected" on this issue. I am not sure
how necessary it is for anyone to "confirm" that this split is a good
one, given that the evidence in favour has been published in textbooks and
commercially available sound recordings for some years, is very strong and is
widely followed. A publication is a publication, whether a book or a journal -
and publications in journals, such as Chapman's publication (which was
published in a journal series) have included discussion of this issue in favour
of a split. Further, Kevin Zimmer, in suggesting a "no" vote here
(that others have followed) is going against his own treatment in
"Handbook of the Birds of the World" and his own approach in the Conopias proposal. The evidence for this
split is stronger than that for the Conopias
species, as lack of sampling of certain regions cannot be raised as an
objection. Finally, these are two range-restricted species, one of which is
threatened. Downgrading one of them to subspecies rank (the effect of a no
vote) will cause BirdLife to change their treatment - and could render the
threatened Brazilian taxon and its habitat less of a conservation priority. I
fail to see anything positive or sensible that would be achieved here by a
"no" vote for proposal A and urge those who have voted to reconsider.
On B, however, the proposal to wait for the published research to come out
seems reasonable. Proposal B, as noted above, was raised for completeness only
(in response to accusations of other proposals being "piecemeal"). If
A should be rejected due to *not* involving a piecemeal approach and bundling
by committee members of votes with B, this could send out a negative message to
persons authoring future proposals."
Comments from Jaramillo: "261a - YES. Ample
available, published data, analysis and opinions exist that all suggest these
two should be divided. It also makes a great deal of biogeographic sense to me.
As far as I can tell, there really is no dissenting opinion out there to keep
these under one species.
261b - NO, let's wait for the analysis."