Proposal (350) to South American Classification Committee
Incluir Xolmis salinarum dentro de X.
rubetra
Nores e Yzurieta (1979) describieron esta
nueva taxa como una subespecie de X. rubetra basados en
caracteres morfológicos, especialmente coloración, y comportamiento. Este taxa
tiene un patrón de colores similar a X. rubetra pero con bastante más
blanco. Además es bastante más chica y no tiene rayas en el pecho (ver foto
adjunta). Ambas especies son gregarias y terrícolas, pero salinarum parece
aún más adaptada a hábitos terrícolas y corre por el suelo a la manera de un
playero (plover).
Hasta 1987 fue considerada como una
subespecie, pero en ese año, Narosky e Yzurieta (Guía para la identificación de
las aves de Argentina y Uruguay) la elevan a especie. De allí en adelante, se
la ha considerado indistintamente como subespecie (por ejemplo Stotz et al.
Neotropical Birds, Nores 1996: Avifauna de la Provincia de Córdoba) o especie
(Ridgely and Tudor: Birds of South America, y en el HBW).
La vegetación de las salinas Grandes y de
Ambargasta, donde habita X. salinarum es en algunos aspectos
similar ecológicamente a la estepa patagónica. Por esta razón, varias especies
patagónicas, durante su migración, pasan el invierno en las salinas o tienen
poblaciones ya establecidas allí; por ejemplo: Leptasthenura aegithaloides,
Asthenes pyrrholeuca, Agriornis microptera, Agriornis murina, Anairetes
flavirostris, Mimus patagonicus y Phrygilus carbonarius.
Xolmis rubetra nidifica en el sur de Argentina y migra en otoño a las provincias
centrales. Evidentemente, X. salinarum deriva de una población de X.
rubetra que se estableció en las salinas. El asunto ahora es determinar si salinarum es
una subespecie muy diferente (megasubespecie) de rubetra o ya ha
alcanzado el status de especie.
Literatura citada:
Nores, M., e Yzurieta, D. 1979. Una nueva
especie y dos nuevas subespecies de Aves (Passeriformes). Acad. Nac. Cienc.
Cba. Misc. No. 61.
Manuel Nores, May 2008
________________________________________________________________________________________________________
Comments from Remsen: "YES. The reason we
currently rank salinarum as a species is largely an accident.
The original draft of Dickinson (2003) started out as treating salinarum
as a species, and that was the one we followed, but by the time the draft went
to press, we had demoted it to subspecies rank given the lack of evidence for
deviating from Manuel's original designation. Therefore, if we were strictly
using the published version of Dickinson (2003), we would treat salinarum as
a subspecies and any proposal would have to provide evidence for species rank.
Not only will a vote yes to correct a change that did not arrive in time, but
also looking at the evidence for species rank ... well there is none. The voice
(a good barometer for species rank in Tyrannidae), for example, is unknown
according to HBW account. Finally, the original discoverer considered it an
isolated, well-marked population of rubetra, and I see no reason to
change from his original or current assessment."
Comments from Cadena: "YES. Manuel's first-hand
experience with the birds and Van's comments convince me that this is the best
course of action."
Comments from Stiles: "YES. I agree with Van's
comments, we need more evidence before contradicting Manuel's judgment on this
point - he surely has more first-hand experience with this taxon, and the
original split was not based upon anything like new evidence."
Comments from Stotz: "YES. I can see no evidence
to support treating this taxon as a distinct species."
Additional comments by Mark
Pearman, Nacho Areta and Hernán Casañas:
Much new data has been acquired in terms of the
basic biology for X. [r.] salinarum since its
type description, yet little has been advanced with the comparative biology of
the more widespread X. (r.) rubetra, since salinarum
has acted like a magnet to ornithologists and birders alike because of its
rarity and restricted range (e.g. Aspiroz 2006). Most of the comparative data,
for the two taxa is either old or historical, but is nevertheless pertinent to
the taxonomy in question; some of it is included in the type description and
some not. Here we add a summary of the distinctions between the two taxa from
published data (to source), and also note that the general consensus in the
literature is rather different from the stated two publications in favour of
subspecies status versus three against (in #350) after finding
another nine books which treat salinarum at species rank (Olrog
1984, Canevari et al. 1991, Chebez 1994, Collar et al.
1994, Stattersfield et al. 1998, Straneck & Carrizo 1991, Mazar
Barnett & Pearman 2001, Di Giacomo 2005, Veiga et al. 2005).
Moreover, we note that it was Claes Christian Olrog (see Olrog 1979) who first
questioned the subspecific status of salinarum using the determination X (r.)
salinarum and later elevated it to species rank (Olrog 1984) well before
Narosky & Yzurieta (1987) did so, as indicated in proposal #350. It is also
noteworthy that in their type description Nores and Yzurieta (1979) wrote
"Diagnostico: esta raza, perfectamente caracterizada, difiere notablemente
de la tipica a tal punto que podria ser considerada una especie distinta."
Plumage distinctions (Sources: Nores & Yzurieta 1979, Aspiroz 2006,
photographs, field observations)
a) Supercilium:- Bold and white in rubetra.
In salinarum, it typically joins across the nape forming a
diadem.
b) Nuchal band: - broad and white (in addition
to the diadem) in salinarum, but lacking altogether in rubetra,
thus salinarum shows two white bands crossing the nape.
c) Back (mantle): - brown in salinarum,
contrasting with its rusty crown, but rusty in rubetra and concolorous
with its crown.
d) Lesser and median upperwing-coverts: - pure
white in salinarum thus exhibiting great contrast with the back, and
rusty brown with white tips to the median wing-coverts (when fresh) in rubetra,
e) Lower rump and uppertail-coverts: - pure
white in salinarum and thus very striking in flight, but brown with fine
whitish fringes to the uppertail-coverts (if one looks closely) rubetra and
thus showing no particular contrast.
e) Lower rump and uppertail-coverts: - pure
white in salinarum and thus very striking in flight, but brown with
fine whitish fringes to the uppertail-coverts (if one looks closely) rubetra and
thus showing no particular contrast.
f) Breast streaking: - none or fine, indistinct
short streaks restricted to the sides of the breast, rarely forming a narrow
pectoral band in salinarum, but heavily streaked over the entire breast
in rubetra.
g) Malar region and ear-coverts: - a fine
isolated black malar at best, or with a few additional sparse black
streaks in this region in salinarum, compared to ear-coverts and malar
region entirely and notably streaked black in rubetra.
- Arguments in favour of
species rank. Subspecies described for X.
irupero, X. pyrope and X. cinerea have all been questioned at
one time or another, are barely diagnosable (Farnsworth & Langham 2004),
and have invariably been accepted by one author only to be discarded by
another. Other members of the genus such as X. coronatus and X.
velatus have always been considered monotypic. Plumage differences between rubetra
and salinarum therefore come as a huge surprise within the genus Xolmis
as a whole (see Vuilleumier 1971, 1994) and are striking both in the field and
among specimens.
To view single photographs of rubetra and
salinarum enter http://picasaweb.google.es/XRubetraSalinarum and click
on "Proyección de diapositivas". More photographs of salinarum
and a host of other Xolmis, Agriornis and Muscisaxicola can
be also found at http://www.avespampa.com.ar/Tyrannidae.htm.
Wing-raising displays described for the genus,
suggest that the strikingly white wing pattern of salinarum might play a
role in reproductive isolation with rubetra. Vuilleumier (1994) noted
that in many species of bush and ground tyrants in the genera Myiotheretes,
Xolmis, Neoxolmis, Agriornis, and Muscisaxicola,
reproductive isolation between closely related species may be correlated with
size or body mass and/or color patterns, although conceivably both size and
color pattern differences could be enhanced during some of the vocal and/or
non-vocal displays.
- Arguments against species
rank. None. Nores (in proposal #350) suggested that salinarum
could be a "megasubspecies". We are not familiar with this term, and
it certainly is not attached to any meaningful Linnean taxonomic category.
Moreover, this statement does not specify which elements would be critical to
support specific, subspecific or "mega-sub-specific" status for salinarum.
Size (Sources: Nores & Yzurieta 1979, museum specimens) All
authors agree that salinarum is smaller than rubetra, and a table
of standard measurements was provided by Nores & Yzurieta (1979) but only
for the holotype. These authors only compared the wing chord of salinarum
(106 mm.) with rubetra (127 mm.). Additional data, although perhaps
arbitrary and with only a small sample for salinarum, are total length
measurements taken at the time of collection, presented on specimen tags as
follows:
rubetra:- 20.83 ± 1.63 cm. (n = 18, IADIZA, MACN)
salinarum- 18.25 ± 0.75 cm. (n = 2, MACN, FML)
These data indicate that salinarum is
almost 12% shorter than rubetra.
- Arguments in favour of
species rank. No such difference in
size exists between any described Xolmis subspecies and its
nominate form. See above for possible role of size in species recognition.
- Arguments against species
rank. None.
Migratory status (Sources: Nores & Yzurieta 1979, Olrog 1979, Di Giacomo
2005, De Lucca & Saggese 1992, Vuilleumier 1994)
rubetra:- An austral migrant breeding in the lowlands, plateaus and
Andean foothills from s. Mendoza, Neuquén, Río Negro, La Pampa and s. Buenos
Aires south to Chubut with one record of a pair from nc. Santa Cruz, and
winters north to Tucumán, se. Santiago del Estero, w. Chaco (unpublished), n.
Santa Fe and Entre Ríos.
salinarum: - Resident with very local movements at the Salinas Grandes, nw.
Córdoba-se. Catamarca and the Salinas de Ambargasta, sw. Santiago de Estero.
Recent records of groups of 4-10 in and around PN Sierra de Las Quijadas, nw.
San Luis suggest another local breeding population.
- Arguments in favour of
species rank. Although we acknowledge
the existence of polymorphism in migratory behaviour in Muscisaxicola (Chesser
2000), the divergent migratory patterns of rubetra and salinarum are
unknown within any other Xolmis species.
- Arguments against species
rank. None.
Sociality (Sources: Serié 1923, Cobos & Miatello 2001)
rubetra- The largest flock on record was a report of 1000 individuals,
and large winter flocks seem to be regular prior to migration and when reaching
wintering grounds before dispersal.
salinarum- The largest flocks on record are 30 to 65 individuals, although
this is unusual and the species is normally found in small groups in winter of
just a few individuals or rarely up to 15 (HC pers. obs.). These are roving
flocks as opposed to migratory flocks.
- Arguments in favour of
species rank. The distinct social
aggregation patterns of rubetra and salinarum are unknown within
any other Xolmis species.
- Arguments against species
rank. None.
Habitat (Sources: Vuilleumier 1994, Farnsworth & Langham 2004,
Di Giacomo 2005)
rubetra- Arid Patagonian shrubsteppe in areas with scattered bushes e.g. Larrea,
Schinus, Baccharis, Chuquiraga and Condalia), often
in adjacent Salicornia beds on salt-impregnated soil; and Patagonian
grass-steppe especially with Festuca bunch-grass with or without
low shrubs; also in rather tall dense Monte desert woodlands. Frequently close
to water. In winter recorded on ploughed fields and Stipa grasslands.
Passage migrants may occur in unusual habitats such as reed and Schoenoplectus
sedgebeds, and even in soya crops (HC per. obs.).
salinarum- Restricted to the borders of open salt flats often close to
saline water courses or standing water; specifically, in areas with a Salicornia
mat covering the salt-impregnated soil or in isolated groups of thorn bush (Atriplex,
Heterostachys, Prosopis reptans and Cyclolepis genistoides);
less commonly at the edge of chaco woodlands bordering the salt flats. Note
that this is a very restricted microhabitat from which the species never strays
far.
- Arguments in favour of
species rank. Rubetra shows a
great deal of plasticity towards its breeding and wintering habitat, whereas
the only habitat of salinarum is very specific, highly restricted,
and different from that of rubetra. Since rubetra is
highly vagile, its absence from the salinas during the breeding season (and
probably also during the winter) suggests that it avoids this habitat, which
would, in turn, suggest that salinarum is reproductively isolated.
- Arguments against species
rank. None.
Nestlings (Sources: Vuilleumier 1994, Cobos & Miatello 2001)
rubetra- Covered with brownish gray down, orange gape.
salinarum- Covered in pearl-grey down. Yellowish bill with whitish
commisure and pink tarsus.
- Arguments in favour of
species rank. Both descriptions are
first hand and relatively recent, but do not coincide.
- Arguments against species
rank. None.
Vocalizations. There is little material on the vocalizations of rubetra and
salinarum, a lack which seems to be symptomatic of the ground-tyrants,
which seldom sing and hence are seldom recorded. Vocalizations have never
played a key role in the taxonomy of the ground-tyrants, and most taxonomically
valuable information seems to be morphological, distributional and ecological
(Vuilleumier 1994). Hence, we see no reason to treat the lack of evidence on
the vocalizations as an impediment to progress in the taxonomy of rubetra
and salinarum.
Legality of taxonomic
change. Salinarum was described as a
subspecies of X. rubetra based on an initial subjective judgment about
its distinctiveness. However, whether it can be arbitrarily elevated to species
rank is a valid question. One answer is that it already has been elevated
(e.g., Olrog 1984, Ridgely & Tudor 1994), and this change has been followed
by the vast majority of authors (see first paragraph of this comments). If this
rank elevation was not possible, we would not have written these comments and
would not be arguing the point with SACC today.
Final comment. In sum, available published evidence clearly shows that rubetra
and salinarum differ dramatically in both ecology and morphology, and
there is no evidence of intergradation or genetic contact between these taxa.
Our own extensive field experience with both taxa is in full agreement with the
published evidence. We propose a NO vote for proposal #350. Voting for NO would
keep salinarum as a valid species, recognising the species-level differences
with other Xolmis based on published evidence, and in agreement with a
widely adopted taxonomy.
New references (not cited in SACC main reference list):
Azpiroz, A. (2006) Photospot: Salinas Monjita Xolmis salinarum.
Neotropical Birding 1: 78-80.
Cobos, V. & Miatello, R. (2001) Descripción del nido, huevo y
pichón de la Monjita Salinera (Neoxolmis salinarum). Hornero 16(1):
47-48.
Collar, N.J., Crosby, M.J. & Stattersfield, A.J. (1994) Birds
to Watch 2: The World List of Threatened Birds. BirdLife Conserv.
Series No.4. BirdLife Internat., Cambridge, U.K.
De Lucca, E.R. & Saggese, M.D. (1992) Aves del Departamento
Deseado, Santa Cruz. Hornero 13(3): 259-260.
Di Giacomo, A.S. ed. (2005) Áreas de importancia para la conservación de
las aves en Argentina. Sitios prioritarios para la conservación de la
biodiversidad. Temas de Naturaleza y Conservación 5. Aves
Argentinas/Asociación Ornitológica del Plata, Buenos Aires.
Farnsworth, A. & Langham, G.M. (2004) Genus Xolmis in:
del Hoyo et al. eds. (2004) Handbook of the Birds of the World. Vol. 9.
Lynx Edicions, Barcelona.
Olrog, C.C. (1984) Las Aves Argentinas: Una Nueva Guía de
Campo. A.P.N., Buenos Aires. Serié, P. (1923) Miscelanea
Ornitología. Hornero 3(2): 189-191.
Stattersfield, A.J., Crosby, M.J., Long, A.J. & Wege, D.C.
(1998) Endemic Bird Areas of the World: Priorities for
Biodiversity Conservation. BirdLife Conservation Series No.7,
Cambridge, U.K.
Straneck, R & Carrizo, G. (1991) Lista de Campo para las
Aves Argentinas. L.O.L.A., Buenos Aires.
Vuilleumier, F. (1994) Nesting, behaviour, distribution, and
speciation of Patagonian and Andean ground tyrants (Myiotheretes, Xolmis,
Neoxolmis, Agriornis, and Muscisaxicola). Ornitologia
Neotropical 5: 1-55.
Additional comments from Remsen: "In view of the
excellent summary above, particularly with respect to comparisons to other Xolmis, I change my vote to
NO."
Additional comments
from Nores: "Los comentarios de Pearman, Areta y Casañas resultan
sorprendente, ya que raramente se da una situación así. O sea que el que
describió el ave propone bajarle el status taxonómico, mientras que los
críticos tratan de buscar todos los elementos posibles para elevar su status.
Siempre es al revés. Aunque a mí personalmente me conviene que mi propuesta sea
rechazada y salinarum sea considerada especie, ya que soy uno de los que la
describió, no he querido influenciar en la propuesta al resto del comité
buscando minuciosamente las diferencias ni tampoco los trabajos que la citan
como especie. Por esta razón, sólo mencioné que era más chica, con mucho más
blanco en el plumaje y sin rayas en el pecho, y cité algunos trabajos que la
consideran subespecie y otros como especie. Aunque los comentarios de Pearman, Areta
y Casañas me parecen buenos, no me sacan la duda de que, si es una subespecie
muy diferenciada o una especie, y de lo que, si estoy seguro, no se trata de
dos especies que difieren dramáticamente en morfología y ecología, como señalan
ellos. A lo sumo, levemente distintas.
"Estos autores también señalan en sus
comentarios que no están familiarizados con el término
"megasubespecie" y que el mismo no está adjuntado a ninguna categoría
taxonómica lineana. Para una definición del término pueden ver Amadon, D. y L.
L. Short. 1976. Treatment of subspecies approaching species status. Syst. Zool.
25:161-167, y una aplicación del mismo en Nores, M. 1992. Bird speciation in
subtropical South America en relation to forest expansion and retraction. Auk
109:346-357."
Comments from Jaramillo: "NO - Well, I could not have
put it better than Pearman et al. My experience with these two species
confirmed to me that they were very different entities. The visual differences
are actually rather well marked, and this is striking for a Tyrannid, and
particularly so for a "ground tyrant relative." I mean you look
at Agriornis, or Muscisaxicola and most good species
(sympatric ones) often differ in elements of size, a bit on plumage tone and at
most a different crown patch color. Xolmis salinarum and rubetra are
visually rather distinct, when compared to other species in this group. Van
worried about the lack of vocal information for this species. Well, these
"ground-tyrant relatives" are notoriously quiet, and they do not seem
to use voice much at all except for a few notable exceptions. Many perform
aerial displays, and at least some Muscisaxicola perform the display but
give no vocal accompaniment, or sometimes just a weak "chip" note
repeated as the bird is in the air. Unlike most tyrants, vocalizations are not
all that important in display in this group. I am sure that vocalizations would
differ if you can obtain some, but they are not important in the actual species-specific
displays these birds use. The fact that "flash patterns" like the
wing patterns differ in Xolmis salinarum and rubetra is probably
more important.
"I also want to underscore how unusual and specific the
habitat of salinarum is, as noted by Pearman et al. In particular, how
different it is from the more typical shrubby Patagonian steppe habitat used by
X. rubetra. Apart from the obvious ecological differences, my guess is
that salinarum probably has some physiological differences in order
to deal with the high levels of salt in its habitat. Just a guess there, but it
gives you a sense for how different the ecological situation is for these two
species, and that does not include the resident vs. migratory nature of the two
forms."
Additional Comments from Cadena: "For the cogent
reasons presented by Pearman et al. and by Alvaro, I change my vote to
NO."
Comments from Robbins: "NO, based on Pearman et
al.'s extensive comments."
Additional comments from Stiles: "In view of the comments
now posted, I agree that salinarum merits species status so will change
my vote to NO. (It is nice to have input from people who know the birds well
when I am not familiar with them!)"
Comments from Pacheco: "NO. Os argumentos reunidos por Pearman, Areta e Casañas
são verdadeiramente suficientes para o tratamento de X. salinarum
em nível de espécie."