Proposal (850) to South American Classification Committee



Use the English name Comb Duck for Sarkidiornis sylvicola


Background and analysis:


Sarkidiornis sensu lato consists of two taxa, the New World sylvicola and the Old World nominate melanotos. These taxa variably have been recognized as a single species or as two species. SACC recently approved a proposal (AOS-SACC 825) to split Comb Duck Sarkidiornis melanotos into two species. SACC adopted the names previously used for groups of the pre-split species by AOU 1998 (American Comb-Duck for sylvicola and African Comb-Duck for melanotos). Approval of the current proposal instead would retain the English name Comb Duck for Sarkidiornis sylvicola and adopt the widely used English name Knob-billed Duck for Sarkidiornis melanotos.


Several English names have been applied to these taxa, but far and away the most common of these are Comb Duck and Knob-billed Duck. There are some general patterns in how these names have been applied, although always with some exceptions. Also note that some sources simply use one name or the other, whereas others acknowledge the existence of both names, but end up choosing one. Most authors who recognize only a single species have used Comb Duck (Phillips 1922, Delacour and Mayr 1945, Delacour 1959, Johnsgard 1978, Soothill and Whitehead 1978, Ripley 1982, Sick 1983, Madge and Burn 1988, Sibley and Monroe 1990, Robson 2000, Dickinson 2003, Hockey et al. 2005, Dickinson and Remsen 2013), but a few opted for Knob-billed Duck (Britton 1980, Brown et al. 1982, Maclean 1988).


Also worth mentioning are regional works that are silent on the question of how many species to recognize. Many of these used Knob-billed Duck (e.g., Newman 1983, Brickell 1988, Lewis and Pomeroy 1989, Dowsett and Forbes-Watson 1993, Barlow and Wacher 1997, Borrow and Demey 2001, Stevenson and Fanshawe 2002), but a few used Comb Duck (e.g., Inskipp et al. 1996, Grimmett et al. 1999).


Many of the references that recognized two species were regional, and so provided an English name only for the relevant taxon. In this category, the split primarily has been adopted by sources dealing with the Old World taxa, the majority of whom have adopted Knob-billed Duck (e.g., Roberts 1940, Mackworth-Praed and Grant 1952, Bannerman 1953, McLachlan and Liversidge 1957, Mackworth-Praed and Grant 1962, Clancey 1964, McLachlan and Liversidge 1978, Clancey 1980). Worth noting here is Rasmussen and Anderton (2005), which used Comb Duck, during a work in which they provisionally recognized only a single species; but these authors split Sarkidiornis a few years later, and adopted Knob-billed Duck for the taxon in South Asia (Rasmussen and Anderton 2012). Gill and Wright (2006) addressed both taxa, adopting Knob-billed Duck for melanotos and Comb Duck for sylvicola; this approach also was taken by the eBird/Clements Checklist v2018.


There is a third way, which is to use modifiers to Comb Duck to distinguish the two taxa. This trend began with authors who still recognized only a single species, and so were giving English names to each subspecies. Delacour (1959) may have been the first in this vein, using Old World Comb Duck for melanotos and American Comb Duck for sylvicola; these names also were adopted by Soothill and Whitehead (1978). Sibley and Monroe (1990), however, proposed African Comb Duck and American Comb Duck, names that also used by the AOU (1983, 1998) and del Hoyo and Collar (2014). Hilty and Brown (1986) and Hilty (2003) suggested South American Comb Duck for sylvicola but did not comment on a name for melanotos. Livezey (1997) split the two, offering Gray-sided Comb-Duck for melanotos and Black-sided Comb-Duck for sylvicola. Ridgely and Greenfield (2001) endorsed either American Comb-Duck or Black-sided Comb-Duck, without suggesting a name for melanotos. Kear (2005) split Sarkidiornis and used the names South American Comb Duck and African Comb Duck. One other point perhaps worthy of consideration is the geographic range of melanotos. It is widespread across sub-Saharan Africa, but also occurs in southern and southeastern Asia, suggesting that African Comb Duck is a poor choice for melanotos.


Our view is that adoption of any version of a modifier + Comb Duck is problematic. Some options on the table, such as "Gray-sided/Black-sided", "South American", or "Old World", result in complex compound bird names. We've all learned to accept such names when we have to, but we prefer simpler name constructions wherever possible. Also note that a subtext of the precedents that were documented above is that the literature on African birds overwhelmingly endorses Knob-billed Duck for melanotos. Admittedly Africa does not represent the whole of the geographic range of melanotos, but Africa clearly is the heart of the range of this species.


An informal survey of field ornithologists active in southeast Asia (David Bakewell, David Bishop, Tim Boucher, Wich'yanan "Jay" Limparungpatthanakij, and Robert Tizard) suggested widespread support for Knob-billed Duck. Praveen J, first author on the recent India checklist (Praveen J. et al. 2016), wrote that "As a general direction, the intent of our checklist is also to gradually transition the regional community to more widely accepted names while minimizing the local impact of the same. Hence, it is also in our interest to transition to Knob-billed Duck". 


Therefore we suggest a simple Comb Duck for sylvicola, and Knob-billed Duck for melanotos.


We are aware of the guiding rule that when a species is split, the parental name (in this case, Comb Duck) is modified or is set aside completely for the daughter species; indeed, arguably we have done as much as anyone has to promote this practice (e.g., AOS-NACC Proposal 2011-C-14). This rule exists for a reason, to reduce confusion when the same English name is applied to two different concepts (sensu lato versus sensu stricto versions of the relevant English name). In the case of the Sarkidiornis, however, we are fairly confident that the risk of confusion from retaining Comb Duck for sylvicola will pose little problem. For one thing, the two taxa are widely allopatric. Furthermore, the name Comb Duck already is standard throughout the range of sylvicola, and Knob-billed Duck is the preferred name in most of the range of melanotos. Finally, given that eBird already split these a year and a half ago, we now have empirical data to bear on the question: there has been no confusion at all with the name Comb Duck in the New World, and while errors in the Old World do occur, these happen at a very low and manageable rate. In short, the simpler names do not represent a case that would, in practice, contribute to the problem that SACC's guidelines on English names are designed to circumvent. Also note that our proposal would be consistent with the pattern exhibited in the case of several Old World/New World splits that recently were adopted by AOS-NACC, e.g. Velvet and White-winged scoters (Melanitta fusca/deglandi), Common and Black scoters (Melanitta niger/americana), and Hen and Northern harriers (Circus cyaneus/hudsonicus).




Our interpretation of the history of the names is that there already exists a clear preference in the literature for Knob-billed Duck for melanotos, at least on the part of ornithologists who have the greatest experience with this taxon. Therefore, we recommend that SACC retain Comb Duck for Sarkidiornis sylvicola, and that SACC go one step further and explicitly endorse Knob-billed Duck for S. melanotos.


Literature Cited:



American Ornithologists' Union. 1983. Check-list of North American birds. Sixth edition. American Ornithologists' Union, Washington, D.C.

American Ornithologists' Union. 1998. Check-list of North American birds. Seventh edition. American Ornithologists' Union, Washington, D.C.

Bannerman, D. A. 1953. The birds of western and equatorial Africa. Volume 1. Oliver and Boyd, London.

Barlow, C., and T. Wacher. 1997. A field guide to birds of The Gambia and Senegal. Yale University Press. New Haven, Connecticut, and London.

Borrow, N., and R. Demey. 2001. A guide to birds of western Africa. Princeton University Press, Princeton, New Jersey.

Brickell, N. 1988. Ducks geese and swans of Africa and its outlying islands. Frandsen, Sandton, South Africa.

Britton, P.L. (editor). 1980. Birds of east Africa. East Africa Natural History Society, Nairobi.

Brown, L.H., E.K. Urban, and K. Newman. 1982. The birds of Africa. Volume I. Academic Press, London.

Clancey, P. A. 1964. The birds of Natal and Zululand. Oliver and Boyd, London.

Clancey, P. A. (editor). 1980. S. A. O. S. checklist of southern African birds. Sigma Press, Pretoria.

Delacour, J. 1959. The waterfowl of the world. Volume 3. Country Life Limited. London.

Delacour, J., and E. Mayr. 1945. The family Anatidae. Wilson Bulletin 57: 3-55.

Dickinson, E. C. (editor). 2003. The Howard and Moore complete checklist of the birds of the world. Third edition. Princeton University Press, New Jersey.

Dickinson, E. C., and J. V. Remsen, Jr. (editors). 2013. The Howard and Moore complete checklist of the birds of the world. Fourth edition. Volume 1. Non-passerines. Aves Press, Eastbourne, United Kingdom.

Dowsett, R. J., and A. D. Forbes-Watson. 1993. Checklist of birds of the Afrotropical and Malagasy regions. Volume 1: species limits and distribution. Tauraco Press, Liège, Belgium.

Gill, F., and M. Wright. 2006. Birds of the world: recommended English names. Princeton University Press, Princeton, New Jersey.

Grimmett, R., C. Inskipp, and T. Inskipp. 1999. A guide to the birds of India, Pakistan, Nepal, Bangladesh, Bhutan, Sri Lanka, and the Maldives. Princeton University Press, Princeton, New Jersey.

Hilty, S. L. 2003. Birds of Venezuela. Second edition. Princeton University Press, Princeton, New Jersey.

Hilty, S. L., and W. L. Brown. 1986. A guide to the birds of Colombia. Princeton University Press, Princeton, New Jersey.

Hockey, P.A.R., W.R.J. Dean, and P.G. Ryan (editors). 2005. Roberts Birds of southern Africa. VII edition. Trustees of the John Voelcker Bird Book Fund, Cape Town.

del Hoyo, J., and N.J. Collar. 2014. HBW and BirdLife International illustrated checklist of the birds of the world. Volume 1. Lynx Edicions, Barcelona.

Inskipp, T., N. Lindsey, and W. Duckworth.  1996. An annotated checklist of the birds of the Oriental Region. Oriental Bird Club, Sandy, Bedfordshire, United Kingdom.

Johnsgard, P. A. 1978. Ducks, geese, and swans of the world. University of Nebraska Press, Lincoln, Nebraska.

Kear, J. (editor). 2005. Ducks, geese and swans. Oxford University Press, Oxford.

Lewis, A., and D. Pomeroy. 1989. A bird atlas of Kenya. A. A. Balkema, Rotterdam.

Livezey, B. C. 1997. A phylogenetic classification of waterfowl (Aves: Anseriformes), including selected fossil species. Annals of Carnegie Museum 66: 457-496.

Mackworth-Praed, C. W., and C. H. B. Grant. 1952. Birds of eastern and north eastern Africa. Volume 1. Longman, London.

Mackworth-Praed, C. W., and C. H. B. Grant. 1962. Birds of the southern third of Africa. Volume 1. Longman, London.

Mackworth-Praed, C. W., and C. H. B. Grant. 1970. Birds of west central and western Africa. Volume 1. Longman, London.

Maclean, G. L. 1988. Roberts' Birds of southern Africa. Fifth edition. New Holland, London.

Madge, S., and H. Burn. 1988. Waterfowl. An identification guide to the ducks, geese and swans of the world. Houghton Mifflin Company, Boston and New York.

McLachlan, G. R., and R. Liversidge. 1957. Roberts Birds of South Africa. Second edition. Cape & Transvaal, Cape Town.

McLachlan, G. R., and R. Liversidge. 1978. Roberts Birds of South Africa. Fourth edition. Cape & Transvaal, Cape Town.

Newman, K. 1983. Newman's birds of southern Africa. MacMillan South Africa, Johannesburg.

Phillips, J. C. 1922. A natural history of the ducks. Volume 1. Houghton Mifflin, Boson.

Praveen, J., R. Jayapal, and A. Pittie. 2016. A checklist of the birds of India. Indian Birds 11: 113-170.

Rasmussen, P. C., and J. C. Anderton. 2005. Birds of South Asia. The Ripley guide. Volume 2: attributes and status. Smithsonian Institution and Lynx Edicions, Washington D.C. and Barcelona.

Rasmussen, P. C., and J. C. Anderton. 2012. Birds of South Asia. The Ripley guide. Volume 2: attributes and status. Second Edition. Smithsonian Institution and Lynx Edicions, Washington D.C. and Barcelona.

Ridgely, R. S., and P. J. Greenfield. 2001. The birds of Ecuador: status, distribution, and taxonomy. Cornell University Press, Ithaca, New York.

Ripley, S. D. 1982. A synopsis of the birds of India and Pakistan together with those of Nepal, Bhutan, Bangladesh and Sri Lanka. Bombay Natural History Society, Bombay.

Roberts, A. 1940. The birds of South Africa. Witherby, London.

Robson, C. 2000. A guide to the birds of southeast Asia. Princeton University Press, Princeton, New Jersey.

Sibley, C. G., and B. L. Monroe, Jr. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, Connecticut.

Sick, H. 1993. Birds in Brazil. A natural history. Princeton University Press, Princeton, New Jersey.

Soothill, E., and P. Whitehead. 1978. Wildfowl of the world. Peerage Books, London.

Stevenson, R., and J. Fanshawe. 2002. Field guide to the birds of East Africa. T & A D Poyser, London.



Tom Schulenberg and Marshall J. Iliff, 20 March 2020




Comments from Remsen:  “YES.  I think this the best solution.  Parenthetically, note that this is a good example of why we should consider separate proposals or subproposals for any English name change, because I predict we would have arrived at this solution rather than just plugging in AOS group name.”


Comments from Jaramillo: “YES.  Put me down as a yes, although it creates a possible confusion. In real life use, the confusion will be minor as noted in the proposal. The benefit of a simpler set of names is a great benefit to the users of English Names.”


Comments from Areta: “Even though my vote does not count, I want to express my support to this option. With common names, usage and practice are to be regarded above all other considerations.”


Comments from Paul Smith:

“The near exclusive application of the name Knob-billed Duck to melanotos versus Comb Duck for sylvicola is not as clear cut as the proposal suggests. The names Knob-billed Duck and Knob-billed Goose are used with approximately equal frequency in the African literature – these should be viewed as two distinct names rather than one name. Furthermore some of the key works on African birds cite both names, thereby reflecting the “synonymy” of these two names for the parent taxon (sensu lato). On the other hand the name Comb Duck is used almost exclusively in the American and Asian literature with a few exceptions, as well as for the parent taxa in most major checklists and most major monographs on waterfowl. Thus the portrayal of Knob-billed Duck/Goose vs Comb Duck being equivalent to Old World versus New World is inaccurate. In fact, even at its most restricted level, it has, until very recently, been equivalent only to Africa versus Asia + America. (See below for a summary of usage in some recent regional works).


Comb Duck

Robson 2002 Birds of Thailand

Wildash 1968 Birds of South Vietnam

Robson 2000 FG Birds of SE Asia

King et al. 1986 Birds of SE Asia

Lekagul 1974 Birds of Thailand

Fleming et al 1979 Birds of Nepal

Grimmett et al. 1979 Birds of Nepal Helm Guide

Shrestha 2001 Birds of Nepal Field Ecology, Natural History and Conservation

Roberts 1991 Birds of Pakistan Vol 1

Kasmierczak 2000 FG to the Birds of the Indian Subcontinent

Grimmett et al. 2001 Pocket Guide to the Birds of the Indian Subcontinent

Grimmett & Inskipp 2003 Birds of Northern India

Grimmett et al. 2008 Birds of Pakistan

Harrison 1999 Birds of Sri Lanka

Samarpan2006 – Photographic Guide to the Birds of India

Ali & Ripley - Pictorial Guide to the Birds of the Indian Subcontinent

Grimmett et al 1998 Helm Birds of the Indian Subcontinent

Ali & Ripley 1987 Compact Handbook of the Birds of India and Pakistan

Ali 1979 The Book of Indian Birds

MacKinnon & Inskipp 2000 FG to the Birds of China

Meyer de Schauensee 1984 The Birds of China

Hawkins et al 2015 Helm FG Birds of Madagascar and the Indian Ocean Islands

Morris & Hawkins 1998 Birds of Madagascar a Photographic Guide


Both names given

(I think that being objective you could make a pretty good argument that these are all key texts in modern African regional literature)

Brown et al. 1981 The Birds of Africa Volume 1

Stevenson & Fanshawe 2002 FG Birds of East Africa

Sinclair & Ryan 2003 Birds of Africa South of the Sahara

Sinclair et al 2002 etc SASOL Birds of Southern Africa


Knob-billed Duck/Goose

Van Perlo 1999 Birds of Southern Africa

Van Perlo 1995 Birds of Eastern Africa

Arlott 2015 Collins FG to Birds of India, Pakistan, Nepal, Bhutan, Bangladesh and Sri Lanka

Van Perlo 2002 Birds of Western and Central Africa

Rasmussen & Anderton 2012 Birds of South Asia The Ripley Guide

Warakagoda et al 2012 Birds of Sri Lanka

Mackworth-Praed 1957 Birds of Eastern and Northeastern Africa

Mackworth-Praed 1969Birds of Southern Third of Africa

Mackworth-Praed 1970Birds of West Central and Western Africa

Williams & Arlott 1989 Collins FG Birds of East Africa

Serle et al. 1977 Birds of West Africa

Morel & Morel 1990 Oiseaux de Senegambie

Barlow et al 1997 FG Birds of the Gambia and Senegal

Guggisberg 1985 Birds of East Africa

Gill 1970 First Guide to South African Birds

Hancock & Weiersbye 2016 Birds of Botswana

Benson et al1973 Birds of Zambia

Redman et al 2009 Birds of the Horn of Africa

Gatter 1997 Birds of Liberia

Ash & Miskell 1998 Birds of Somalia

Sinclair1984 FG to Birds of South Africa

Newman 1991 Newmans Birds of Southern Africa (Updated Ed)

Prozesky1980 FG to the Birds of Southern Africa

McLachlan & Liversidge 1972 Roberts Birds of Southern Africa

Langrand 1990 Guide to the birds of Madagascar


“Regards the recommended name according to the NACC guidelines for application of English names, ( if the committee was to decide to follow the NACC guidelines (at this point awaiting a proposal and approval), I would draw attention to the following:



C. New and Modified Names Based on Changes to Classification

1. Typical species splits. In the case of true phylogenetic daughter species formerly treated as a single parental species, the usual policy is to create new names for each daughter species. …This practice is designed to prevent confusion in the literature as to what taxonomic entity the parental name (e.g., Solitary Vireo) refers. Note that this differs from the procedure used for scientific names, which mandates (via ICZN) that the name of the nominate form remain unchanged. In support of the principle of stability, the choice of new names strongly considers existing names for the daughter species in widely used older literature (e.g., Ridgway and Friedmann 1901-1946) as well as any names proposed for the new species in publications supporting the change in species limits.



“As highlighted in the proposal under Art C1 the usual practice is for daughter species to be given new names and the choice of new names should consider existing names for the daughter species in support of the principle of stability. Two exceptions are mandated for this:



1.1 Asymmetry in range size. When one or more of the new daughter species are essentially peripheral isolates or have similarly small ranges compared to the other daughter species, then the parental name may be retained for the widespread, familiar daughter species to maintain stability……. The Committee recognizes that judging the degree of asymmetry is subjective and that borderline cases will sometimes occur.

1.2 Special cases. In exceptional cases, when a parental name is much more appropriate for one of the daughter species, and when no truly appropriate substitute name can be found, a parental name may be retained for that daughter. For example, in the case of the split of Winter Wren (Troglodytes hiemalis), the parental name Winter Wren was retained for the migratory eastern species, whereas the novel name Pacific Wren was created for the largely resident western species (T. pacificus). In this case the retained English name of the eastern species hiemalis also reflects its scientific name, which means “of winter” (Jobling 2010).



“Given that Comb Duck was the name attributed to the parent taxon in the majority of the non-African “pre-split” literature, under Art 1.1 both the names Comb Duck and Knob-billed Duck/Goose are, according to the guidelines, available only for the widespread Old World melanotos, not the more restricted New World sylvicola which has a considerably smaller geographic range. Nor can it justifiably be considered an “exceptional case” under Art 1.2 as a "truly appropriate" substitute name “South American Comb Duck” is available and in use in the most comprehensive monograph of the Anseriformes yet published (Kear 2005). Understandably this may not be a name that people are enthusiastic about, but it is not inappropriate and the natural desire to “improve” on this name is warned against under Art A1.



A. Principles and Procedures

1. Stability of English names. The NACC recognizes that there are substantial benefits to nomenclatural stability and that long-established English names should only be changed after careful deliberation and for good cause. As detailed in AOU (1983), NACC policy is to “retain well established names for well-known and widely distributed species, even if the group name or a modifier is not precisely accurate, universally appropriate, or descriptively the best possible.” The NACC has long interpreted this policy as a caution against the ever-present temptation to ‘improve’ well-established English names and this remains an important principle. In practice, this means that proposals to the NACC advocating a change to a long-established English name must present a strongly compelling, well-researched, and balanced rationale.



“The meaning of “well-established” is open to interpretation, but certainly when considering stability of usage any name that is in current usage is by definition more “well-established” than any invented new name. On the other hand global lists such as IOC and Cornell Birds of the World have recently adopted the names as proposed by the proposal (Comb Duck and Knob-billed Duck), so there is an argument of stability to be made by following suit - given that "South American" becomes essentially obsolete as part of the name if there is only one Comb Duck (examples of needlessly long names like this do exist nonetheless e.g., White-naped Xenopsaris, Sharp-tailed Streamcreeper, Black-capped Donacobius etc).


“Two other potentially complicating issues of relevance were not raised in the proposal.


“• In previous proposals the importance of not insinuating sister species relationships with English names where they do not exist has been highlighted before (e.g. Slaty Thrush), the other side of this same argument is that where sister species relationships do exist then an effort should be made to reflect them in the English names. South American Comb Duck opens the door to doing this provided the Old World taxon takes a similar modifier. However in "endorsing" a name that does not take the modifier we consciously break the sister species relationship implied by retaining it. The committee needs to decide whether consistency in approach with regard to this issue outweighs the view of the proposal authors that “adoption of any version of a modifier + Comb Duck is problematic”. Or to put it another way, whether reflecting sister species relationships in common names is a policy that the committee is seeking to adopt, and whether looking to keep that option open in this case is desirable or unimportant. Electing to keep the name Comb Duck for sylvicola “claims” the name for the American taxon however and restricts the options available for melanotos closing the door to any name that reflects relationships.


“• It is justifiably debatable whether NACC/SACC guidelines are applicable in cases where species have cosmopolitan ranges and decisions have ramifications beyond the checklist area. In such cases there is an argument that attempting to fall in line with other authorities might result in a more stable outcome than trying to influence them to change with new names. The adoption of Comb Duck following IOC and Cornell Birds of the World might be fairly argued under that circumstance. Whether or not SACC has the authority to “endorse” names of birds in other geographic regions without engaging in dialogue is, however, open to question, and before taking this unnecessary step it is perhaps worthy of consideration as to whether the committee would feel bound by the decisions of others if the boot was on the other foot.”


Comments from Zimmer: “YES”.  This is a tough one.  Paul Smith, in his comments, raises some valid concerns about the proposed retention of Comb Duck for sylvicola.  The temptation is to add a modifier (I would prefer “American” to “South American”, both for brevity, and, in acknowledgement that there are records from Panama.) to “Comb Duck”, but then, if Old World authorities end up sticking with Knob-billed Duck for melanotos, then the implied sister relationship is lost from the English names, and we are left with an overly long name like “White-naped Xenopsaris” or “Black-capped Donacobius” that doesn’t serve any real purpose.  Perhaps it is my Africa bias at work (apologies to Asia), but I’ve always known melanotos by “Knob-billed Duck”, and I’ve always used “Comb Duck” in the field for sylvicola.  I think this is one of those cases where, regardless of what we do, someone is going to be unhappy, and we’ll be accused of inconsistent application of some guideline.  So, in anticipation that “Knob-billed Duck” will prevail as the English name in the Old World, I think the retention of “Comb Duck” for sylvicola is the way to go.  I also would have no problem with adding the modifier “American” to Comb Duck, but would be resistant to the unwieldy “South American Comb-Duck” or “Black-sided Comb-Duck”.


Additional comments from Remsen: “I’m changing my vote to NO, mainly on the basis that Paul has pointed out that “Comb Duck” is in widespread use in Asia.  Paul also made several other good points.  Also, given that species rank for these two is barely justified, Comb vs. Knob-billed implies a degree of difference that doesn’t exist; in other words, this is one of those cases in which I think the longer, compound names are actually better because they highlight that similarity e.g. (American Comb-Duck and Old World Comb-Duck).  As we all know, in the field we would just call them “Comb Duck” anyway --- the compound name is simply for technical reference.  The problem is that Knob-billed does seem to be in widespread usage in Africa.  Further, NACC, Clements, etc., have already gone with the simpler names.