Proposal (15) to South American Classification Committee

 

Elevate Butorides sundevalli (Lava Heron) to species rank

 

Effect on South American CL: this proposal would split the Striated Heron, Butorides striatus, into two species, B. striatus and B. sundevalli.

 

Background: Two forms of Butorides herons breed in the Galapagos Islands, a typical pale taxon evidently indistinguishable from mainland B. striatus, and an endemic dark taxon, sundevalli. These are either treated as conspecific (e.g., Martínez-Vilata and Motis 1992), as is the current status in our baseline list, or as separate species (Harris 1982). The endemic taxon is a common nester on all islands (Harris 1973, 1982); striatus-like birds are known only from seven islands.

 

Here's the direct quote from Harris (1973):

 

"The situation regarding these species is confused. B. sundevalli is endemic and common in coastal areas of all the islands, and until recently there had been no suggestion that another Butorides sp. ever occurred in the Galápagos. However, birds resembling B. striatus have been recorded on Isabela (nesting), Santa Cruz (nesting), Fernandina, Duncan, Santa Cruz, San Cristobál, and Pinta. Present knowledge is insufficient to ascertain whether there are two species of Butorides breeding in Galápagos which hybridize (as intermediates occur) or whether there is one, very variable species. If B. striatus does indeed breed, it is not a recent colonizer since skins assignable to the species were collected by the Academy Expedition 1905-6 (L. C. Binford, unpubl. data).”

 

Payne (1974) examined 58 specimens from the Galapagos and concluded the following:

 

" show all possible intermediate plumage colours." " high proportion of intermediate birds indicates considerable successful breeding and genetic recombination." " The Galapagos herons are variable, but nearly all adults are separable from adults of continental populations." " The Lava Heron is probably best considered a distinct subspecies, B. striatus sundevalli, at least until studies on breeding pairs have been made on the islands."

 

Payne's table indicates that only 13 are really "pure" Lava Heron phenotype, and 18 have dark gray or gray underparts, darker than South American striatus but paler than typical "Lava Heron." Only two were as pale as South American striatus, but can still be distinguished from them. Payne speculated that the variability might be the result of multiple invasions of the Galapagos by striatus stock at different times.

 

Kushlan (1983), who studied the breeding behavior of Lava Herons (but evidently not the local Striated-like phenotype), noted a number of subtle differences in behavior between Lava Herons and what had been published for South American B. striatus but concluded:

 

"Pair formation of the Lava Heron generally resembled that of the Green-backed Heron described by Meyerriecks (1960). The substantial similarities are added evidence of a close relationship and lend no support for doubting Payne's (1974) view of the conspecificity of the three forms on Butorides."

 

Kushlan noted the following differences in sundevalli from striatus: (1) female performs stretch at nest site, (2) does bill snaps, and (3) doesn't sway. Additional minor differences were also noted. However, he emphasized that his N was small on Galapagos populations studies, and that unstudied populations of year-round resident striatus populations there or elsewhere might also show these differences (which he interpreted as having to do with year-round territoriality and nesting three times per year).

 

Kushlan also noted differences between the breeding bare part colors of the two, but seemed not to attach significance to them. Lava legs turn from gray to reddish-orange, whereas Striated (and Green) legs go from orange to orange-red. Lava lores go from green to bright cobalt blue, whereas in Striated, they turn blue-black. [For those without access to color plates, note that sundevalli is almost all black, by far the most distinct plumage phenotype in the global striatus group.]

 

Recommendation: I will vote NO on my own proposal, which began as an investigation that I thought would conclude that species rank was merited for sundevalli. Although we can all list many additional data sets required to make a truly informed decision on this one, the above is all that we have, as far as I can tell. Based on these data, I'm not really sure what "sundevalli" is, and I suspect that Payne's idea of multiple colonizations is correct, producing a population that is an amalgam of various striatus infusions. On the other hand, if we maintain striatus and virescens as separate species, then perhaps sundevalli ought to be ranked as a species also. On the other other hand, the whole complex needs an overhaul _ how can striatus and virescens be kept separate when Old world striatus are continued to be considered as conspecific?

 

Nonetheless, I'm intrigued by the difference in bare-part colors and displays. What I need to know for me to vote YES on species rank is whether those striatus-like phenotypes also share those same differences from mainland striatus   at that point I'd lean towards species rank for sundevalli as a highly variable species.

 

English name: The taxon sundevalli is called "Lava Heron" by those authors who consider it a separate species, including Harris (1982).

 

Lit Cit:

Harris, M. P. 1973. The Galápagos avifauna. Condor 75: 265-278.

Harris, M. P. 1982. A field guide to the birds of the Galapagos. Collins, London.

Kushlan, J. A. 1983. Pair formation behaviour of the Galapagos Lava Heron. Wilson Bull. 95: 118-121.

Martínez-Vilata, A. and A. Motis. 1992. Family Ardeidae (herons). Pp. 376-429 in del Hoyo et al., Handbook of the birds of the World, Vol. 1. Lynx Edicions, Barcelona.

Payne, R. B. 1974. Species limits and variation of the New World Green Herons Butorides virescens and Striated Herons B. striatus. Bull. Brit. Orn. Club 94: 81-88.

 

Van Remsen, 17 May. 2002

 

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Comments from Doug Stotz: "On Lava Heron, it seems to me that the situation on the Galapagos is likely analogous to the Slate-colored Coot situation, with a variable population with one form resembling the near relative (striatus in this case, Fulica americana in the other). I have to admit that it seems hard for me to imagine that sundevalli and striatus could be conspecific, if striatus and virescens are not. It further seems hard to imagine that Old World and New World striatus are best treated as conspecific. But maybe I am actually arguing here for the status quo, until somebody figures this all out...

 

From Manuel Nores: "Si estoy de acuerdo con elevar a Butorides striatus sundevallii al rango de especie. El color negro y las partes desnudas de la cara celestes parece que son suficientes."

 

From Mark Robbins: "Although the Hayes' article didn't provide any definitive answers, if we are going to recognize both virescens and striatus as species, then we should elevate the Lava Heron to species level. Thus, I vote "yes" for this proposal.

 

From Gary Stiles:  "Lava Heron a species: A very qualified YES. The argument for raising (again) virescens to species rank was that the 'intermediate' buff-necked birds represented variation within striatus, rather than hybrids. By the same logic, one could say that variation from light to dark birds on the Galapagos was simply variation within sundevalli, with the additional point that all have the same distinctive soft part colors. Given the sedentary nature of striatus, multiple colonizations doesnęt seem all that likely given the distances involved. I am not aware of any detailed comparisons of morphology or displays in OW vs. NW striatus. So, if the AOU recognizes virescens as a species, I think that consistency demands that we recognize sundevalli as well. If at some point the AOU reverses itself and 'sinks' virescens, then we reconsider! Un the meantime, more data on those Galápagos pale birds seems in order.

 

From Tom Schulenberg: "What a nightmare.

 

"I am voting "No" on this proposal, largely because I don't feel that I understand what is going on, and I am reluctant to make any changes if I don't understand what is going on.

 

"I have no field experience with sundevalli. The Field Museum has five specimens: one juvenile/immature that is "gray", two "black" specimens, and two "gray" adults. The two gray adults clearly are paler than are the classic black sundevalli, but also are darker than are most if not all of our striatus from Ecuador and Peru (and also lack any trace of the rusty or buff color typically present on the necks of South American striatus).

"Clearly, with only these few specimens I can't confirm (or refute) Payne's suggestion that plumage color in Galapagos Butorides spans the full spectrum between gray and black. It would be nice to know whether indeed that is the case. This is especially on my mind after I queried two people close at hand who each had made multiple visits to the Galapagos. Both were of the opinion that all to almost all of the Butorides that they had seen in the Galapagos clearly were "black" *or* "gray". (Although their recollections as to the relative abundances of the two plumages did differ!). This kind of limited anecdotal data, not supported by specimens, is weak, I know, but since it seems to fly right into the face of what Payne reported I feel as if I have to call everything into question: what *is* the prevalence of the "gray" plumage? Is there intergradation or not? and if so, how extensive is it? Is there assortative mating? etc.

 

"I don't think that recognition of Butorides virescens as a species compels us to recognize sundevalli. The recognition of virescens as a species was driven, I thought, not only by the fact that virescens and striatus are "different", but also that the breeding distributions of virescens and striatus approach one another in Panama with little evidence of hybridization. It's not clear to me how that situation would be relevant to whatever is happening on the Galapagos.

 

"So, to properly evaluate the situation on the Galapagos, I think we need to know a lot more about what several things that we don't know (but that might not be that hard to get to the bottom of, if someone put their mind to it: Van, can you interest David Wiedenfeld in pursuing this?).

 

From Alvaro Jaramillo:  "Yes, the plumage and bare part differences (important in pair formation presumably) between sundevalli and striatus are enough for me to consider this taxon a separate species. The open question is what the grey individuals on the Galapagos are, grey morph of sundevalli or real striatus that have recently colonized the islands.”