Anas diazi
Status: Accidental in fall.
Documentation: Photograph: 30 October 2024 Scottsbluff WTP, Scotts Bluff Co (Mlodinow, eBird Checklist – 30 Oct 2024 – Scottsbluff WTP; Brogie 2025).
Taxonomy: No subspecies are recognized (Gill et al 2022).
See related taxonomic discussions under Mallard and Mottled Duck.
Whether Mexican Duck is a valid species has been a matter of debate, although it was recently elevated to species status by AOS (Chesser et al 2020) based primarily on genomic studies by Lavretsky et al (2019). The work of Bielefield et al (2016) and Lavretsky et al (2015, 2019) was followed up by genomic studies that confirmed species level differences between Mexican Duck and Mallard (Brown et al 2022). Mexican Duck had been considered by some authors, including AOU (1998), a subspecies (as A. p. diazi) of Mallard, A. platyrhynchos (see also Johnsgard 1975, Sibley and Monroe 1990). AOU denied a proposal by Banks to elevate it to species status citing a study by Hubbard (1977) who concluded there was “extensive introgression” with Mallard in the northern parts of Mexican Duck’s range. However, the evidence provided in Hubbard in support of this conclusion is at best equivocal: on a scale of 0-36 (“pure” Mexican Duck = 36) the scores ranged from 34.5 at the southern edge of its range to 28.3 in the north. While this shallow cline suggests Mallard introgression at some time in the past (McCracken et al 2001, Avise 1990) and to an uncertain extent currently (Lavretsky et al 2015, Leukering and Mlodinow 2012), recent studies have found assortative mating in areas where Mallard occurs with Mexican Duck (Bevill 1970, Webster 2006, Baldassarre 2014). In addition, very few Mallards occur in the breeding range of Mexican Duck during periods when pairing occurs (Baldassarre 2014, Leukering and Mlodinow 2012). Furthermore, recent genomic work by Brown et al (2022) found that “25% of genetically pure, immature male Mexican ducks of the northern population naturally displayed mallard-like traits in their formative plumage.” When the 97%-accurate key developed by these authors to identify Mexican Ducks and possibly hybrids was applied to 55 museum specimens, only four of the 14 specimens originally classified as phenotypic hybrids were truly hybrids (Brown et al 2022).
For these reasons, we follow the decision of AOS (Chesser et al 2020) to elevate Mexican Duck to full species status. While there is evidence that American Black, Mottled, and Mexican Ducks all possess some degree of Mallard introgression, taxonomic consistency would also indicate treatment of Mexican Duck as a full species (Leukering and Mlodinow 2012, Drilling et al 2020).
For Nebraska records of hybrids between Mexican Duck and Mallard, see Mallard x Mexican Duck (hybrid).
Record: A single Mexican Duck was found and photographed by Steven Mlodinow and seen as well by Stephen Brenner at Scottsbluff WTP, Scotts Bluff Co 30 Oct 2024 (eBird Checklist – 30 Oct 2024 – Scottsbluff WTP; Brogie 2025).
There are three additional recent reports that were not accepted by NOURC.
One was with Mallards in a small pond near Grant, Perkins Co 14 Sep 2019 (Mlodinow; https://ebird.org/checklist/S59808685). The description provided follows: “Overall, it had a dark brown body contrasting somewhat sharply with paler head and neck. The underparts were uniformly dark from chest thru undertail coverts. The tail was entirely brown. The speculum looked to have narrower borders than that of a [Mallard], more so to the rear than in front. The head and neck were pale brown with blackish on crown and with a blackish eyeline. No black mark at gape. No pale tan unstreaked area as in [Mottled Duck]. The bill was orange with dusky along culmen and towards tip. No distinct black blotches.” Presumably the same bird was reported the next morning,15 Sep, by Ross Silcock. The reports were not accepted by NOURC which stated: “Probably correct, but not beyond reasonable doubt” (Brogie 2020).
Another was at Scottsbluff WTP, Scotts Bluff Co 11 Jul 2022, photographed, and described as follows (Steve Mlodinow, eBird.org): “While sorting through the pile of Mallards at the sewage ponds, including a number of juveniles and eclipse males, I found a bird that stood out as a Mexican Duck. Eclipse and juvenile Mallards can make [Mexican Duck] identification rather tricky from late June into August, but this bird truly looked different. I watched it in fair light for 10-15 minutes, in very good light for 5-10 minutes, and then was interrupted by a nice gentleman from the wastewater treatment facility alerting me to the gates were to be closed soon. After he drove off, I could not relocate the duck. The back, scaps, folded wings, sides, and chest looked uniformly dark brown (note, that the upper tail and undertail coverts were concolorous with the rest of the bird, not black as in [Mallard] and [Mexican Duck x Mallard]. The neck and head, however, were contrastingly pale dingy brown, with a narrow dark brown eyeline that did not quite reach the hind crown, and a dark brown crown. The tail had white in it, but less so than nearby [Mallard]. It was the size of a male [Mallard] (note that the male [Mallard] in the photos with the bird is a domestic [Mallard], not wild type). During the time I watched the bird, it stretched its wing out several times, revealing a rather narrow trailing edge to the speculum, and a narrow white leading edge. I could not determine the color of the speculum. As it was stretching, at least some of the center of the belly could be seen, and it was the same color as the sides. The bill was olive. I sent photos to Andy Engilis, who has been involved in research of Mexican Duck phenotype based on genetic confirmation of [identification]. His response (and note, he was responding re: what he could see in the photos, and not with the added information re: wing pattern, belly color) was: “Hi Steve — I am wondering if this bird is indeed a Mexican Duck. We have a poor understanding of the alternate plumage of Mexican Ducks, and I suspect this bird might just represent that. The tertials look really worn and coupled with the black undertail and a few other features, are indicative of a Formative bird at this time of the year. My interpretation is that this bird is a [Mexican Duck] in first prealternate plumage (or molt).” A pure [Mallard] in formative plumage should not be so dark, nor have the contrastingly pale head/neck. Though juv male [Mallard] often have olive bill color, formative should have a yellow bill (and formative plumage in male [Mallard] usually not attained until September). Additionally, eclipse male [Mallard] and juv [Mallard] typically have a blacker and broader eyeline that meets the crown. The wing pattern does not fit [Mallard] . Some white in tail is not unusual in formative [Mexican Duck] (and many have some green on head, curve to central tail feathers, features which this bird lacked). The lack of [Mallard] traits would also argue against hybrid. The face is not pale enough for Mottled Duck, the border to the speculum were white, unlike Mottled Duck, and there was not black at the gape, as is true in many Mottled Ducks.” This report was not accepted by NOURC as “lacking substantial evidence for a first state record” (Brogie 2023).
One was reported at Crescent Lake NWR 1 Aug 2024 and described as follows (Mlodinow, eBird Checklist – 1 Aug 2024 – Crescent Lake NWR“; Brogie 2025). Adult male in worn plumage. Rather typical appearance. Blackish brown body including evenly dark underparts noted when bird was standing. Chest not darker nor warmer brown. Undertail and uppertail coverts mottled, not solid black as in Mallard. Tail brown. Chest contrasted sharply with paler brown head and neck. Face grayer and more streaked than that of Mottled Duck but paler and less marked than in Am Black Duck. Blackish crown and dark line from bill , through eye, but not reaching crown. Bill olive. White anterior border to speculum distinctly narrower than that of Mallard. Posterior white border similar to that of Mallard. Apparently paired with adult female Mallard. Seen roughly halfway down south side, though would check muddy stretch at far western end of south side, as many ducks typically roost there, but not today as there was a Bald Eagle in attendance. I found two photos of some use, though both are not definitive and were taken in less-than-ideal light.”
There are two older reports, neither accepted (Bray et al 1986, Silcock et al 1986). A specimen referred to as Mexican Duck was collected 17 Oct 1921 in Cherry Co (Bent 1923). This is a female #973 in the Field Museum of Natural History, Chicago, but is now considered likely a hybrid between Mallard and American Black Duck (David Willard, personal communication). The second report is of an adult male shot in Rock Co 19 Oct 1969 (Menzel 1970). Although its identity as a Mexican Duck was confirmed by Paul Johnsgard and the bird showed no evidence of captivity, the possibility of its being an escaped bird could not be eliminated (Menzel 1970). Menzel (1970) noted that at that time Mexican Ducks were kept in captivity in Hall Co and that escapes occurred occasionally.
A dark female mallard type paired with a male Mallard 20 Jun 1993 in Sioux Co and reported by Ross Silcock as an American Black Duck may have been a Mexican Duck or a Mallard x Mexican Duck hybrid based on current knowledge. The identification as American Black Duck was considered “Most unusual for season and location” (Grzybowski 1993).
There are numerous records for Colorado, including one in May in Sedgwick Co only 2.3 mi south of Deuel Co, Nebraska, and singles in Logan Co in Jun, Yuma Co in Jun, and Kit Carson Co Apr and Jun (eBird.org, accessed Apr 2023). There are no records for Kansas (Thompson et al 2011, eBird.org accessed April 2023), and only one for Oklahoma, Dec 2022 (eBird.org, accessed Apr 2023).
Comments: It is likely that more will occur northward as part of an ongoing low-density northward push into the Great Plains possibly due to severe drought in the southwestern US but also concomitant with northward range expansion by other southern waterbirds like Neotropic Cormorant and Black-bellied Whistling-Duck (Steven Mlodinow, personal communication).
Abbreviations
AOS: American Ornithological Society (formerly AOU)
AOU: American Ornithologists’ Union
NOURC: Nebraska Ornithologists’ Union Records Committee
NWR: National Wildlife Refuge
WTP: Water Treatment Plant
Literature Cited
American Ornithologists’ Union [AOU]. 1998. The AOU Check-list of North American birds, 7th ed. Allen Press, Lawrence, Kansas, USA.
Avise, J.C., C.D. Ankney, and W.S. Nelson. 1990. Mitochondrial gene trees and the evolutionary relationship of Mallard and Black Ducks. Evolution 44: 1109-1119.
Baldassarre, G. 2014. Ducks, geese, and swans of North America. Johns Hopkins University Press, Baltimore, Maryland, USA.
Bent, A.C. 1923. Life histories of North American wild fowl. Bulletin of the United States National Museum 126. Dover Publications Reprint 1962, New York, New York, USA.
Bevill, W.V., Jr. 1970. Effects of supplemental stocking and habitat development on abundance of Mexican Ducks. Master’s thesis, New Mexico State University, Las Cruces, New Mexico, USA.
Bielefeld, R.R., A. Engilis, J.C. Feddersen, J.M. Eadie, M.D. Tringali, and R.J. Benedict. 2016. Is it a mottled duck? The key is in the feathers. Wildlife Society Bulletin, 40, 446– 455. https://doi.org/10.1002/wsb.665.
Bray, T.E., B.K. Padelford, and W.R. Silcock. 1986. The birds of Nebraska: A critically evaluated list. Published by the authors, Bellevue, Nebraska, USA.
Brogie, M.A. 2020. 2019 (31st) Report of the NOU Records Committee. NBR 88: 124-134.
Brogie, M.A. 2023. 2022 (34th) Report of the NOU Records Committee. NBR 91: 114-122.
Brogie, M.A. 2025. NBR, in press.
Brown, J.I., F. Hernández, A. Engilis Jr., Blanca E. Hernández‑Baños, D. Collins, and P. Lavretsky. 2022. Genomic and morphological data shed light on the complexities of shared ancestry between closely related duck species. Scientifc Reports 12:10212. https://doi.org/10.1038/s41598-022-14270-2.
Chesser, R.T., S.M. Billerman, K.J. Burns, C. Cicero, J.L. Dunn, A.W. Kratter, I.J. Lovette, N.A. Mason, P.C. Rasmussen, J.V. Remsen Jr., D.F. and K. WSixty-first Supplement to the American Ornithological Society’s Check-list of North American Birds. Auk 137, Issue 3, 1 July 2020, ukaa030, https://doi.org/10.1093/auk/ukaa030.
Drilling, N., S.O. Williams III, R.D. Titman, and F. McKinney. 2020. Mexican Duck (Anas diazi), version 1.0. In Birds of the World (P. G. Rodewald and B. K. Keeney, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.mexduc.01.
Gill, F., D. Donsker, and P. Rasmussen (Eds). 2022. IOC World Bird List (v 12.2). Doi 10.14344/IOC.ML.12.2. http://www.worldbirdnames.org/.
Grzybowski, J.A. 1993. The Summer Season. North American Birds 47: 1122-1124.
Hubbard, J.H. 1977. The biological and taxonomic status of the Mexican Duck. Bull. New Mexico Dept. Game Fish 16.
Johnsgard, P.A. 1975. Waterfowl of North America. University of Indiana Press, Bloomington, Indiana, USA.
Lavretsky, P., J.M. DaCosta, B.E. Hernandez-Banos, A. Engilis Jr., M.D. Sorenson, and J.L. Peters. 2015. Speciation genomics and a role for the Z chromosome in the early stages of divergence between Mexican ducks and mallards. Molecular Ecology 24: 5364–5378.
Lavretsky, P., T. Janzen, and K.G. McCracken. 2019. Identifying hybrids & the genomics of hybridization: Mallards & American black ducks of Eastern North America. Ecology and Evolution 9: 3470-3490. https://doi.org/10.1002/ece3.4981Citations: 10.
Leukering, T., and S.G. Mlodinow. 2012. The Mexican Duck in Colorado: Identification and Occurrence. Colorado Birds 46: 296-309.
McCracken, K.G., W.P. Johnson, and F.H. Sheldon. 2001. Molecular population genetics, phylogeography, and conservation biology of the mottled duck (Anas fulvigula). Conservation Genetics 2: 87-102.
Menzel, K.E. 1970. Mexican Duck. NBR 38: 89-90.
Sibley, C.G., and B.L. Monroe, Jr. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, Connecticut, USA.
Silcock, W.R., T.E. Bray, and B.K. Padelford. 1986. Mexican Duck in Nebraska. NBR 54: 40-41.
Thompson, M.C., C.A. Ely, B. Gress, C. Otte, S.T. Patti, D. Seibel, and E.A. Young. 2011. Birds of Kansas. University Press of Kansas, Lawrence, Kansas, USA.
Webster. R. 2006. The Status of Mottled Duck (Anas fulvigula) in Arizona. Arizona Birds Online 2: 6-9.
Recommended Citation
Silcock, W.R., and J.G. Jorgensen. 2025. Mexican Duck (Anas diazi). In Birds of Nebraska — Online. www.BirdsofNebraska.org
Birds of Nebraska – Online
Updated 11 Feb 2025