Proposal (493) to South American Classification Committee
Treat Basileuterus hypoleucus as conspecific
with Basileuterus culicivorus
Effect
on South American CL: This proposal would lump two species
currently recognized as separate species on the baseline list.
Background:
Although described as separate species on account of obvious plumage
differences, doubt has frequently been cast about the specific validity of Basileuterus hypoleucus. Hellmayr (1935)
commented that the ranges of the two overlapped considerably in Brazil and
Paraguay and that the presence of intermediate birds "casts serious doubt
on their specific distinctness". Mixed pairs of the two species have been
reported from Brazil (Willis 1986) and Paraguay (Robbins et al 1999), and it is
not uncommon for hypoleucus specimens
to show some degree of yellow on their otherwise whitish underparts (Remsen
& Traylor 1989, Robbins et al 1999, FAUNA Paraguay 2011). Robbins et al
(1999) noted that all presumed hybrids are of the hypoleucus-type, being white with yellow patches, and that culicivorus-type yellow birds with white
patches have never been reported. Sick (1993) considered the two species to be
conspecific and remnants of a population that had undergone geographic
separation as a result of ancient geoclimatic events but that were now coming
into contact again. He considered the voices of the two species to be
identical.
Contrary
to other authors, Hayes (1995) stated that the vocalisations of B. hypoleucus are in fact closer to B. flaveolus than to B. culicivorus and mentioned
undocumented observations of a mixed family of these two species in Dpto.
Concepción, Paraguay. Additionally, he noted a difference in habitat preference,
with B. culicivorus preferring more
humid forest, citing this and widespread sympatry of range as evidence that
they are two distinct but closely related species. Robbins et al (1999) later
clarified that the vocalisations of B. hypoleucus
are not similar to flaveolus and
added that vocalisations of culicivorus
and hypoleucus in Dpto Concepción, Paraguay are so similar that both
species react strongly to playback of taped recordings of the others calls. Additionally, they clarified that
the mixed family reported by Hayes did not refer to paired birds but to birds
“intermingling together” (F. Hayes pers. comm.).
In
a phylogenetic review of the Parulidae, Lovette et al (2010) provided data that
confirmed a close relationship between the species and treated them as sister
taxa. Focusing only on the B. culicivorus
complex, Vilaça & Santos (2010)
used molecular studies to demonstrate that B.
hypoleucus did not form a monophyletic clade within the complex and was in
fact related to B. culicivorus
populations from Brazil and Paraguay. They stated:
"Although
it is not currently possible to distinguish genetically between these two
species, the restricted area of occurrence of B. hypoleucus could suggest either that this is an incipient
species in the process of differentiation or the white color is a restricted
polymorphism of a major taxon, B.
culicivorus. Our results and the observation that
these recognized species do not own [sic] differences in vocalization or
morphometry (Silva 1992), might be a strong
indication that these belong to a single species."
Using both mitochondrial and nuclear markers, and corroborated by
the morphological study of Silva (1992), they concluded that the two taxa
should be lumped into a single species.
Recommendation:
I recommend a "YES" vote on this proposal because of the convincing
molecular evidence presented by Vilaça
& Santos (2010), the known hybridisation between the two
"species" and the fact that they respond strongly to recordings of
each other’s vocalisations. The name Basileuterus
culicivorus (Lichtenstein) would be the correct name for the species. The
status of the form hypoleucus
(Bonaparte) is currently unresolved and further studies are required to
determine whether it is in fact a valid subspecies or just a restricted colour
morph.
Literature Cited
FAUNA PARAGUAY. 2011. Basileuterus
hypoleucus. Online images
www.faunaparaguay.com/basileuterus_hypoleucus.html.
HAYES, F.E. 1995. Status, Distribution and Biogeography of the Birds of
Paraguay. ABA Monographs in Field Ornithology 1. 230p.
HELLMAYR, C.
E. 1935. Catalogue of birds of the Americas. Field Mus. Nat. Hist. Publ., Zool.
Ser., vol. 13., pt. 8.
LOVETTE, I. J., J. PÉREZ-EMÁN, J. P. SULLIVAN, R. C. BANKS, I.
FLORENTINO, S. CÓRDOBA-CÓRDOBA, M. ECHEVERRY-GALVIS, F. K. BARKER, K. J. BURNS,
J. KLICKA, S. M. LANYON, AND E. BERMINGHAM.
2010. A comprehensive multilocus
phylogeny for the wood-warblers and a revised classification of the
Parulidae (Aves). Molecular Phylogenetics and
Evolution 57: 753-770.
REMSEN, J.V. Jr., TRAYLOR M.A. 1989. An Annotated List of the Birds of
Bolivia. Buteo Books, Vermillion, South Dakota. 79 pp.
ROBBINS, M.B., R.C. FAUCETT, AND N.H. RICE. 1999. Avifauna of a
Paraguayan cerrado locality: Parque Nacional Serrania San Luis, Depto.
Concepcion. Wilson Bulletin 11: 216-218.
SICK, H. 1993. Birds in Brazil. Princeton University Press, New Jersey.
703pp.
SILVA, W.R. 1992. Padrões ecológicos,
bioacústicos, biogeográficos e filogenéticos do complexo Basileuterus culicivorus (Aves, Parulidae) e demais espécies
brasileiras do gênero. Departamento de Ecologia. Universidade de Campinas,
Campinas. p.132.
VILAÇA, S. T., AND F. R. SANTOS.
2010. Biogeographic history of
the species complex Basileuterus
culicivorus (Aves, Parulidae).
Molecular Phylogenetics Evolution 57: 585-597.
WILLIS, E.O. 1986. Vireos, wood warblers and warblers as ant followers. Gerfaut
76: 177-186.
Paul
Smith, August 2011
_________________________________________________________________________________________________________
Comments from Remsen:
“YES. With first-hand experience with
both taxa in Bolivia, I became highly suspicious of the species rank of hypoleucus in 1984 – songs and calls
sounded identical to me, and populations we sampled in Dpto. Santa Cruz showed
signs of intergradation. Now, we have
some actual data that show that hypoleucus
is a pale-bellied form of southern culicivorus.”
Comments from Stiles: “YES – all the
evidence seems to fit treating hypoleucus
as a pale-bellied race of culicivorus
rather than a species.”
Comments from Robbins: “YES, based on our
Paraguay data (Robbins et al. 1995) coupled with the Vilca & Santos genetic
data it would seem best to treat hypoleucus
as conspecific with culicivorus.
Comments from Pacheco: “YES. In my personal experience, I agree
that the vocalizations of both taxa involved are
virtually indistinguishable. The simple
calls can be something different but seem to fall within
the range of complex B. culicivorus. I've found in eastern Minas Gerais
pairs with individuals tending to each of the taxa. Given the results of Vilaça &
Santos (2010) - in combination with those older Weber
Silva (1992) – I vote yes.”
Comments from Stotz: “YES.
This makes me “sad,” but this has always been out there. There is certainly a habitat difference
between the two taxa with culicivorus
more of a humid forest species and hypoleuca
more in cerrado and gallery forest. But
there are plenty of places where these forms come in contact with
intergradation known. Vocally they are
very similar if not identical.”
Comments from Pérez: “YES. Evidence available is against
retention of B. hypoleucus as
species. This is an interesting case showing that potentially independent
evolutionary lineages might not persist in the face of their habitat dynamics
and the lack of geographical or ecological barriers. It would be great to
investigate the potential hybridization between these taxa and the patterns and
mechanisms of plumage variation.”
Comments from Zimmer: “YES since there appears to be solid evidence of intergradation, the vocalizations are doubtfully distinct (and, in reciprocal playback experiments, the two taxa respond to one another’s voice), and molecular evidence for single-species treatment is convincing. Doug’s comments regarding the habitat distinctions are spot-on, but I’m afraid the crush of other evidence overwhelms this as a consideration.”