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.
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.”