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
________________________________________________________________________________________
Comments from 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 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 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 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
doesn´t 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 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.”