Proposal (1092) to South American Classification Committee

Treat Chiloe Steamer Duck Tachyeres ketru as species distinct from Magellanic Steamer Duck Tachyeres pteneres

Effect on SACC list

If this proposal passes, it will result in the recognition of Chiloe Steamer Duck Tachyeres ketru as a species distinct from Magellanic Steamer Duck Tachyeres pteneres.

Background

The current SACC note reads: López-Lanús & Costa (2026) described a new species of Tachyeres, T. ketru, for the northern population of T. pteneres. SACC proposal badly needed.

Since the first decade of the 21st century several experts in the field have discussed a distinct form of T. pteneres from the Chiloe/Aysén region of Chile, which has also been widely described in scientific databases as a distinct “undescribed form” or “likely a different species.” The taxon has long been well known to be distinguishable by coloration of the bill.

New Information

López-Lanús & Costa (2026) describe a new taxon from the Chiloe/Aysén region of Chile on the basis of significant differences in ecology, vocalizations, and the coloration and sexual dichromatism of bare parts.

Ecology

López-Lanús & Costa (2026) described ecological differences between the northern and southern populations of T. pteneres in detail. The Taitao Peninsula, located at roughly 46° south, serves as the main barrier between the proposed T. ketru in the north and T. pteneres in the south. The peninsula also divides different ecoregions comprising substantially different coastal conditions which are reflected in the habitat preferences of the two populations. While both species are strongly tied to the presence of the macroalgae Macrocystis pyrifera, T. ketru occurs in more sheltered waterways north of Taitao, which align with the presence of a “protected coastal ecotype” of M. pyrifera. South of the peninsula, T. pteneres inhabits more exposed shorelines that experience powerful ocean wave action and cold currents and are associated with a different, morphologically distinct ecotype of M. pyrifera.

A map of the study area and ecoregions associated with P. ketru and P. pteneres, from López-Lanús & Costa (2026), summarizing descriptions from Jaramillo et al. (2006), Spalding et al. (2007), V. Häussermann and G. Försterra [unpublished 2015] in Rovira and Herreros (2016) and Rovira and Herreros (2016).

Vocalizations

López-Lanús & Costa (2026) found that all Tachyeres taxa, including the proposed T. ketru, can be segregated consistently on the basis of the contact calls made by males. This call type is shown to be homologous between all taxa in the genus, and each taxon has a distinct and consistent frequency range and frequency distribution that allows for reliable identification based on visual inspection of spectrograms. The authors also note that T. pteneres and T. ketru can be distinguished auditorily by observers. The authors found that the frequency distributions of contact vocalizations of T. pteneres south of the Taitao are more similar to those of T. leucocephalus of Argentina than they are to those of the proposed T. ketru. Additionally, the frequency distributions of contact calls of T. ketru are more similar to those of T. patachonicus than they are to those of T. pteneres. Playback experiments do not appear to be applicable because the birds were not observed to respond territorially to auditory stimuli without visual cues (López-Lanús & Costa, 2026).

From López-Lanús & Costa (2026), detail of individual contact calls from males of all Tachyeres taxa.

From López-Lanús & Costa (2026), examples of note sequences from contact calls of male Tachyeres.

From López-Lanús & Costa (2026), oscillograms representative of contact calls from P. pteneres and P. ketru.

Coloration and Sexual Dichromatism of Bare Parts

López-Lanús & Costa (2026) showed that the proposed T. ketru can reliably be distinguished from T. pteneres on the basis of coloration and sexual dichromatism of bare parts in living individuals (although the distinguishing pigmentation is not reliably preserved in museum specimens). They also demonstrated that the distinguishing traits do not vary clinally across the distribution of T. ketru or T. pteneres. Although diet, which may vary between the two ecoregions inhabited by the two populations, can impact the coloration of bare parts, the presence of the diagnostic greenish-gray subnarial patch in T. ketru is shown to be independent of both the intensity of yellow/orange pigmentation of the rest of the bill as well as the season of observation. In addition to possessing a subnarial patch which distinguishes them from T. pteneres, T. ketru also demonstrates sexual dichromatism in the coloration of the bill, with females possessing a much more pronounced subnarial patch than males. In contrast, sexual dichromatism is not observed in the bill coloration of T. pteneres:

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From López-Lanús & Costa (2026), photos demonstrating typical bill pattern and coloration in pairs of T. ketru and T. pteneres.

From López-Lanús & Costa (2026), closeup images of bill patterning in male and female T. ketru (A) and T. pteneres (B).

From López-Lanús & Costa (2026), distribution of T. ketru and T. pteneres. Numbers indicate localities of sound records included in their analysis, while alphanumeric codes indicate relevant photographic specimens. The authors remind readers to “Note the coincidence of the distributions of both taxa with the ecoregions in the Study Area shown in Map 1 [included above].”

From López-Lanús & Costa (2026), a summary painting of male and female of T. ketru (A) and T. pteneres (B). Note subnarial patch present in both male and female T. ketru, as well as sexual dichromatism of this field mark in this species. T. pteneres does not display subnarial patch or sexual dichromatism of the bill.

Additional Comments

Genetic data would greatly improve our understanding of the taxonomy of Tachyeres, especially of the boundary between T. ketru and T. pteneres, but substantial differences in ecology, vocalizations, and coloration and sexual dichromatism of the bill seem to provide sufficient evidence to seriously consider elevation to species status at this time.

Notes on Nomenclature and Etymology

López-Lanús & Costa (2026) suggest the name “Chiloe Steamerduck” for the new species, but following the current standards used in AviList, and in alignment with an ongoing trend of reducing hyphenation, the name would perhaps best be “Chiloe Steamer Duck.”

The specific epithet “ketru” proposed by López-Lanús & Costa (2026) comes from the name for Tachyeres in the local indigenous Mapuche language (Mapudungun), used especially for this taxon.

López-Lanús & Costa (2026) provide extensive justification for the use of the epithet “ketru” instead of “chiloensis” for the newly described taxon by demonstrating the absence of the principle of priority. Although the epithet “chiloensis” occurs in the 1782 and 1810 editions of Saggio sulla Storia Naturale del Chili from J. I. Molina, the description provided in that text is sufficiently unclear and self-contradictory as to not be reliably assignable to any taxon when assessed with any scrutiny.

Additionally, the recognition of T. ketru as a species distinct from T. pteneres would invalidate the current neotype of T. pteneres. Because of the lack of a specimen from the original description from the Strait of Magellan, a neotype was selected, but an individual from the island of Chiloe was chosen instead of one from the area of the original description, and is thus representative of T. ketru and not of the intended T. pteneres. The authors thus propose a holotype and new neotype for T. ketru and T. pteneres respectively, both held at the American Museum of Natural History in New York, USA. The proposed holotype of P. ketru is from Chiloe Island, Chile, in 1914, whereas the new neotype proposed by the authors for P. pteneres is from the Beagle Channel, Chile in 1915.

Voting and Recommendations

Likely best resolved with two votes:

A) Species limits: We recommend a YES vote to recognize T. ketru as a species distinct from T. pteneres.

B) English names: We recommend a YES vote to adopt the name Chiloe Steamer Duck for T. ketru and Magellanic Steamer Duck for T. pteneres. [Note from Remsen – in SACC orthography, the group name is Steamer-Duck]

References

López-Lanús, B. and M. Costa (2026). A new species of Steamerduck (Anatidae: Tachyeres) from the Chiloé region, Chile, finally confirmed as a taxon distinct from Tachyeres pteneres. The Audiornis Journal of Bioacoustics and Field Ornithology, 5:2-130. https://audiornis.org/journal/articulos/AUDIORNIS%20(2026)%20Number%2005%20February%20pp%201-130%20Tachyeres%20ketru%20SP%20NOV.pdf

eBird.org, Flightless Steamer Duck, https://ebird.org/species/flistd1

Nick Kowalske, October 2026

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Vote tracking chart:

https://www.museum.lsu.edu/~Remsen/SACCPropChart1044+.htm