Proposal (441) to South American Classification Committee
Split Zimmerius
improbus from Z. vilissimus
Effect of Proposal: If it passes, this proposal would result in
recognition of Zimmerius improbus (Venezuelan Tyrannulet) as a
species separate from Z. vilissimus (Paltry Tyrannulet). This treatment is reflected by essentially
all other authorities dealing with this issue that have been published over the
last 15 years. We recently reviewed the
basis for split and lumped treatments in Donegan et al. (2010). By way of background, we moved the Colombian
checklist to generally follow SACC treatments as from 2007, but did not accept
this SACC lump as one of a handful of exceptions.
Discussion: In Donegan et al.
(2010), we reviewed the literature on this species and studied a sample of
sound recordings of both groups.
Sonograms were published. We
stated as follows:
“We
recognized Ridgely & Tudor (1994)'s split of these species in Salaman et
al. (2001, 2007, 2008a, 2009). Essentially all other major works dealing with
the two populations over the last 20 years have adopted the same approach (e.g. Sibley & Monroe 1990, AOU 1998, 2010, Hilty 2003,
Fitzpatrick 2004, Restall et al. 2006, Rheindt et al. 2008, Ridgely & Tudor
2009, Gill & Donsker 2010). Remsen et al. (2010) is effectively the ‘last
man standing’ in lumping this species with Paltry Tyrannulet Z. vilissimus, leading this to be an
exception to our decision in 2007 to follow Remsen et al.’s taxonomy in the
Colombian checklist. That decision was re-evaluated this year.
“Venezuelan
Tyrannulet Z. improbus of the Perijá
and Mérida Andes and coastal Venezuela is a bigger bird than Paltry Tyrannulet Z. vilissimus. As is well known (e.g.
Ridgely & Tudor 1994), the former also has a considerably larger bill and
most different head plumage. A review of sound recordings at www.xeno-canto.org
further supports the split, as noted by Ridgely & Tudor (1994), Fitzpatrick
(2004) and Rheindt et al. (2008). Z.
vilissimus has a short 'pip' as its call, whereas Venezuelan Tyrannulet of
the Merida and Perijá ranges gives a longer whistle with a most different note
shape (Figure 3). These differences
are equivalent to those between other Zimmerius
treated as species (comparing with sonograms in Rheindt et al. 2008).
“Habitat
requirements (lower montane vs. lowland) are also quite distinct. Although
there are no recordings available from the Perijá range or Santa Marta, one
would expect populations in that region to be related to Andean populations
given their similarity in plumage and other aspects of morphology.
[Comment received from Trevor Ellery after the paper had gone to
the printers: "Z. improbus
occurs occasionally in the lower reaches of the El Dorado reserve in Santa
Marta. Birds respond to playback of recordings of Z. improbus from Venezuela but I have not been able to get any
sound recordings yet."]
“We
see no reason to adopt Remsen et al. (2010)'s more cautious approach in light
of the obvious vocal and morphological differences between these species, which
are substantial in the context of Tyrannidae. Votes on the Colombian checklist
forum were in favor of maintaining our current (split) treatment with 10-0
votes in favor. In light of all these factors, we will maintain our current
treatment of recognizing these two species.”
Recommendation: A “YES” vote. It would be nice to have some recordings from
Perijá (tamae) and Santa Marta (petersi) were this to be a novel
proposal for a split. However,
populations from these regions are very clearly closely allied to the improbus group on account of their
morphology. It is probably overdue for
SACC to align itself with essentially all other authorities on this
treatment. “YES” to split; “NO” to lump.
References:
Donegan, T., Salaman, P., Caro, D.
& McMullan, M. 2010. Revision of the status of bird species occurring in
Colombia 2010. Conservación Colombiana
13: 25-54.
Other references are cited in this
paper.
Thomas Donegan, May 2010
Comments solicited from Frank Rheindt:
“I support Thomas Donegan's proposal to split Zimmerius
improbus from Z. vilissimus.
“Based on their different
looks and sounds, there is no doubt the two taxa are different species, and
people have known this for years and treated them as "field guide
splits". Such treatment is not good enough for SACC, which requires
peer-reviewed publication of results, but I believe that Donegan et al.'s
(2010) somewhat crude analysis of Xeno Canto sonograms nudges this split across
the finish line.
“One little inaccuracy in the proposal that
remains to be pointed out is that Rheindt et al. (2008) never opined on the
taxonomic treatment of Z. improbus and only mentioned the taxon briefly
in passing, noting that it's recognized by HBW (Fitzpatrick 2004). We have
recently obtained a generous tissue loan of Z. improbus and intend to
include its DNA in an upcoming follow-up study to Rheindt et al. (2008). I have
a feeling that it won't even emerge as the sister to Z. vilissimus, just
the same way that Z. albigularis and Z. acer emerged far from
their supposed conspecifics.”
Comments from Robbins:
“NO. There is no
question that improbus deserves
species status. However, given that Frank Rheindt is about to produce a
genetic data set that includes improbus
I’m quite copasetic with waiting for his results before making a
decision. Thus, a “no” vote for the hopefully short term.”
Comments from Stotz:
“YES. I think the required data are
there. Although I understand Mark
wanting to wait for DNA, the fact that even if DNA did not show this is
distinct from vilissimus, I would
still vote to split, makes the DNA results seem irrelevant.”
Comments from Zimmer: “YES. I don’t think there is any doubt that these are separate species. I would say that Frank Rheindt’s comment that “Donegan et al.’s (2010) somewhat crude analysis of Xeno Canto sonograms nudges this split across the finish line” pretty much sums up my assessment of the amount of published evidence in support of the split.”