Proposal (566) to South American Classification Committee
Treat Geotrygon
purpurata as a separate species from G.
saphirina
Proposal: This
proposal, if it passes, would result in G.
purpurata being split from G.
saphirina, a treatment accepted by several other authorities, including
several major publications on pigeons over the last decade and others listed in
Donegan & Salaman (2012).
Discussion:
This split was rejected in proposal 105 (http://www.museum.lsu.edu/~Remsen/SACCprop105.html). This was back in 2004, before sources
like xeno-canto were really available or had good samples and consistent with
the SACC's then approach to other "field guide splits" around this
time. Most committee members cited
a lack of vocal data supporting the split, and no dissenting comments in
support of the split are evident. There
are two new publications relevant to this issue published in the last couple of
years, and a further relevant paper was overlooked in 2004.
Molecular data:
Brumfield &
Capparella (1996: http://www.museum.lsu.edu/brumfield/pubs/brum96.pdf), using
three samples of each group, found unusually high divergence between purpurata and saphirina for lowland conspecifics with a Chocó / Amazonian
distribution. More recently,
Johnson & Weckstein (2011) studied a single Ecuadorian purpurata and single Peruvian saphirina
in a phylogeny including good sampling of new world pigeons. They found strong support for a sister
relationship and moderate (modeled c.1.2
million years) differentiation, consistent with that observed between samples
of Russet-crowned Quail-Dove Geotrygon
goldmani & Chiriquí or Rufous-breasted Ground-Dove G. chiriquensis and those between nominate Grey-fronted Dove Leptotila rufaxilla & Yungas Dove L. megalura, but also consistent with
intraspecific variation in widespread Leptotila
verreauxi. One of their BEAST
chronogram-based phylogenies is set out below. Note these two Geotrygon
species at the bottom of the tree, and the relative depth of the branch.
Neither studies reject
monophyly for the combined group (and the latter study found strong support for
this). But both studies show a
relatively deep division, consistent with Chocó/Amazonia splits generally and
those between several Neotropical pigeon species.
Vocal data
Donegan & Salaman (2012: link below)
published various data on these pigeon species' natural history, voice and
conservation, and included a rare photograph of purpurata in life by Juan Carlos Luna. We measured two acoustic variables and found no overlap for
the length of the main note in songs between saphirina and purpurata (see
figure reproduced below). The
differences are statistically significant, but despite there being no observed
overlap, the data did not meet the Isler et
al. '97.5% using t-distributions'
diagnosability test. Acoustic
frequency also varies between the taxa, with statistical significance found,
but not diagnosability. G. saphirina (in some but not all
recordings) varies the frequency of songs but G. purpurata has flat notes in all recordings. It is this variability of frequency
that past transcriptions of vocal differences in field guides seem to have
concentrated on as a difference, but this feature is non-diagnostic: saphirina also gives flatter calls. Song length does however separate out the sample fully based on recorded
data. It would be speculative to
conclude whether, with a greater sample size, the ideal 97.5% diagnosability
test would be met or not. The
vocal differences are, however, very real and substantial, and have gone
largely overlooked or misunderstood in the literature until Salaman &
Donegan (2012). See our figure 3,
reproduced below (song length on x
axis, frequency on y axis; p=purpurata; s=saphirina).
As discussed in our paper, given the way
in which these songs are made, by birds inhaling a lot of air, expanding the
chest, and then exhaling through their nostrils without bill movements (see
this video:
http://ibc.lynxeds.com/video/sapphire-quail-dove-geotrygon-saphirina/bird-singing-forest-while-perched-eye-level),
such vocal differences seem likely to be constrained by physiological factors
and not a result of learning.
The two species seem to have different
elevational ranges, and, hence one assumes, ecological requirements. In particular, purpurata is a foothill bird that has not been recorded on the
Chocó "floor" whilst saphirina
is found in western Amazonia.
The molecular and vocal data seem consistent with other
pigeon splits. The split passes
Tobias et al.'s "species scoring tests" also. A subsequent communication with Nigel
Collar revealed that their team last year independently assessed purpurata as (just) meeting the
"species scoring test", disregarding vocal differentiation data
(which were not available to them).
We were more conservative in assessing plumage scores and had purpurata 'crossing the line' as a
result of 2 points out of 3 for the highly differentiated and statistically
significant (but not statistically diagnosable) vocal differences. Neither the paper nor this proposal is
intended as an endorsement of this score system, but it is a useful further indication
for allopatric birds like these.
On the basis of all the above, my own view, and that of all our team who
work on the Colombian checklist, is that these molecular and vocal data tip the
balance in favour of treating purpurata
separately under a conservative BSC approach. We appreciate that really hardcore Petersian lumpers could
legitimately take another view given monophyly and failure to meet the toughest
statistical tests of diagnosability.
We also discussed the conservation status
of purpurata. Although not relevant to taxonomic
determinations, it is perhaps of note that (whether lumped or split), these are
both threatened forest-dependent birds, VU when lumped based on the recent
papers on Amazonian deforestation rates; and with G. purpurata recommended in our paper for EN treatment if split. This decision is, therefore, not solely
of relevance to listers or bird checklist accuracy fanatics.
Vernacular
names: Quoting from our paper: "Hellmayr & Conover (1942) used the name Purple Quail-Dove, which is
appropriate given that this is the most purple Geotrygon. However, this
name seems to have been overlooked in the recent literature in favour of
Indigo-crowned (e.g. Ridgely & Greenfield 2001, Restall et al.
2006)." "Purple"
for purpurata is a nice name and
transliteration, which mirrors "Sapphire". Perhaps a separate proposal on that issue is needed if this
passes? We would suggest retaining
saphirina's existing vernacular name
(Sapphire) given its appropriateness in light of plumage and the scientific
name, relative sizes of distributions (this name would still apply to by far
the greater part of the old combined range) and history of usage in other
sources.
References:
Brumfield, R.
T. & Capparella, A. P. 1996. Historical divergence of birds in
north-western South America: a molecular perspective on the role of vicariant
events. Evolution 50(4): 1607-1624.
Donegan, T.M. & Salaman, P.G.W. 2012. Vocal
differentiation and conservation of Indigo-crowned Quail-Dove Geotrygon purpurata. Conservación Colombiana 17: 15-19. http://www.proaves.org/proaves/images/RCC/Con_Col_17_15-19_Geotrygon.pdf
Johnson, K.P. & Weckstein, J. 2011. The
Central American land bridge as an engine of diversification in new world
doves. Journal of Biogeography 38: 1069-1076.
Other papers mentioned are cited in the above.
Thomas
Donegan, November 2012
Comments from Robbins: “YES, given the plumage and genetic (especially
when compared to other recognized Geotrygon
species) data. The relatively
minor differences in vocalizations do not concern me, as most Geotrygon primary vocalizations sound
very similar.”
Comments from Stiles: “YES, given the genetic and biogeographical
information; the vocal data are also suggestive, if not wholly conclusive.”
Comments
from Pacheco: “YES, from the new genetic and vocal data.”