Proposal (822) to South American Classification Committee

 

Treat Theristicus branickii as a separate species from T. melanopis

 

Background:

         Theristicus melanopis was formerly treated as a subspecies of T. caudatus, although currently the two are widely treated as separate species. It was Steinbacher (1979) that first divided the species, although there the three forms, including branickii, were given species status. It is unclear why the treatment of melanopis as a species became widely accepted whereas branickii was not; perhaps it is due to these two taxa being more similar to each other in plumage than they are to caudatus.

         The biogeography of melanopis and branickii bear some comment. The two overlap widely latitudinally but are typically allopatric, with branickii found at higher elevations than melanopis. The distribution of melanopis becomes patchy from northern Chile north to northern Peru, with limited areas where it can be found in Peru. Curiously in Ecuador, an isolated population of branickii is found in the highlands near Antisana.

 

New Information:

         Collar and Bird (2011) studied specimens to assess morphological differences between melanopis and branickii.  They found consistent and non-overlapping differences between the two, in measurements as well as plumage.  Particularly interesting is the shape difference, with branickii having a substantially shorter bill (essentially no overlap).  Furthermore, branickii is noticeably longer tailed, shorter-legged and longer-winged. Overall size is similar between the two.  Perhaps these shape differences, particularly leg/bill length suggest different foraging habits, or habitat in which they forage.  Collar and Bird (2011) confirmed plumage differences noted by others (for example Jaramillo 2003), with the difference of melanopis showing an obvious facial wattle, which is missing in branickii.  There are consistent plumage differences in the distribution of cinnamon on the head and neck, as well as differences in the extent of back on the belly.  Collar and Bird did not assess biological information to clarify species status, but they concluded that the two are separate species based on a “Tobias Score.”

Most interesting are recent observations by Vizcarra (2009, 2010) in Tacna, Peru, and additional data noted in eBird by observers in nearby Lluta, Chile, where melanopis and branickii have been found sympatrically.  Vizcarra (2010) recorded nesting of T. m. melanopis in the Tacna area, where the birds use cliffs for nesting and lowland agricultural areas for foraging.  Vizcarra (2009) detailed some interesting behavior when the two forms are together.  Thus far, no branickii have been found nesting in the Tacna area, and Vizcarra suggested that they move in from highland sites. However, it is equally likely that they may breed nearby, as occurrence, at least in northern Chile, is year-round. There are no populations of branickii in the Puna grasslands immediately above (in elevation) these sites in Peru and Chile.  Vizcarra (2009) noted that when the two forms are together, the flocks may forage near each other but maintain separation from each other.  Vizcarra also noted that near a colony of melanopis, a single branickii was seen, and that the two reacted aggressively to each other.  The presence of branickii while melanopis was breeding is of particular interest.  Although this sympatry is limited, lack of any hybridization as well as agonistic behavior to each other, and behavioral separation of flocks suggest that the two forms are treating each other as biologically different species.  The possibility of interbreeding is there, but there is no evidence that it happens.

         In the Lluta Valley in northern Chile, branickii occurs throughout the year (eBird data).  The form melanopis is also present, although less common. In almost all cases flocks of the two forms segregate, and the observations are nearly always of flocks ranging from 6 to 20 or so in size. This behavioral segregation here is similar to what has been noted in Peru. The year-round records of branickii in Lluta, Chile, suggest they might be nearby breeders rather than migrants moving in from the Altiplano as suggested by Vizcarra (2009). The distributional data suggests that the two forms are sympatric here, although it would be more clear-cut if a colony of branickii could be found in the general area. Particular areas of the Lluta Valley are the most frequented by branickii, and perhaps these areas are the closest to where the breeding colony is?

There is one record in Chile of a trio including the two forms.  Note, however, that even in the photos, the two melanopis were close together, and the branickii off by itself. Also note the extremely different proportions, with branickii low to the ground and shorter billed. These shape differences suggest different foraging technique, at least clarifies an ecological separation. Photos here:

https://ebird.org/view/checklist/S54692899

 

Recommendation:

         I suggest that branickii be separated as a biological species different from melanopis. Plumage differences are present and consistent between the two. The presence/lack of an important character that is presumably for display (wattle) seems particularly noteworthy as a difference between these two species. Published descriptions of these forms have not been good at noting the extreme difference in shape between these two forms, suggesting a different ecology.  But most important is the apparent sympatry in southern Peru and Chile; at least the two are present year-round in the same areas and melanopis has been confirmed to breed there. There is no evidence of interbreeding or mixing of any type.  Even in areas where the two types can be found foraging, they segregate into single-species flocks.  The data are still limited but clear that these two forms are treating each other as different when they are found together.

 

English Names:

I see no good reason to alter the established names for these two forms. The widespread melanopis would keep Black-faced Ibis. The form branickii has been called Andean Ibis. Both of these names are in wide usage.  Although Andean Ibis is similar to the name Puna Ibis (Plegadis ridgwayi), it does not seem to cause confusion.

 

Literature:

COLLAR, N.J AND J. P. BIRD. 2011. Phenotypic discrimination of the Andean Ibis. Wilson Bulletin 123: 459–463.

JARAMILLO, A. 2003. Field guide to the birds of Chile. Christopher Helm, London, United Kingdom.

STEINBACHER, J.  1979. Family Threskiornithidae. Pp. 253-268 in "Check-list of birds of the World, Vol. 1, Second Edition" (E. Mayr and G. W. Cottrell, eds.). Museum of Comparative Zoology, Cambridge, Massachusetts.

VIZCARRA, J.K. 2009. Observaciones de Theristicus melanopis melanopis y Theristicus melanopis branickii en el Distrito de Ite, Sur del Perú. Boletín Chileno de Ornitología 15: 104-110.

VIZCARRA, J.K. 2010. Descubrimiento de dos sitios de anidamiento de Theristicus melanopis melanopis en Tacna, sur de Perú. Cotinga 32: 111-112.

 

Alvaro Jaramillo, May 2019

 

Note on voting procedure from Remsen: Unless otherwise explained in your comments, a YES vote also endorses the English names suggested above by Alvaro.  I would agree with Alvaro that because branickii has often been treated as a separate species, the usual guidelines concerning parent-daughter names from lumps and splits do not apply.

 

 

 

Comments from Remsen:  “YES.  Alvaro emphasizes that the available data are weak but in aggregate I think they place burden-of-proof on conspecific status.  Comparing color and shape differences among the three species in this group gives me the qualitative impression that accepted species limits in the ibis genus Plegadis are much narrower, further fortifying the claim that burden-of-proof should be on treating these two Theristicus as the same species.”

 

Comments from Stiles: “YES for splitting branickii from melanopis - plumage and morphology seem distinctive, and preferred habitats also differ.. the behavioral observations certainly do not fit with conspecifity either.”

 

Comments from Claramunt: “YES. I think all the evidence clearly points to the presence of two different species.”

 

Comments from Robbins: “YES.  The evidence at hand does seem to support recognition of branickii as a species, so for now, I vote "yes" for the split.  However, this may need to be revisited when, and if, "mixed" colonies are located.  Nonetheless, given the extensive hybridization between Plegadis falcinellus and P. chihi, limited hybridization may have little bearing on our treatment of Theristicus taxa.”

 

Comments from Stotz: “YES.  When melanopis was split from caudatus, the split of branickii was already considered, and I would say it was not done out of caution.  I think the current evidence does suggest that they are best treated as separate species.”

 

Comments from Pacheco: “YES. There are good reasons to treat T. branickii as a species under BSC and no good reason to keep it subordinated to T. melanopis.”