Ecology and Behavior of Steamer Ducks (Anatidae: Tachyeres)

Introduction

Steamer-ducks (Anatidae: Tachyeres) are large, gray-and white denizens of marine coastlines of southern South America and the Falkand Islands; only the Flying Steamer-Ducks (Tachyeres patachonicus) extend their habitats to freshwater lakes of the Andes. Although steamer-ducks appeared in the narratives of naturalists visiting the regions since the late 1500s, Darwin (18 ) was the first to propose that two species of the group existed in the areas visited during the famous voyage of the H.M.S. Beagle. This primary division was to initiate 150 years of debate concerning the flight capacity and number of species in the genus (first referred to Anas, then segregated in Micropterus, than replaced by Tachyeres). Landmark works, reviewed by Livezey and Humphrey (1992) in the classification of the genus, include Lowe (1934), Murphy (1936), and Humphrey and Thompson (1980). Current taxonomy (Livezey and Humphrey 1992) recognizes one widespread, regionally flighted and variably migratory species (Tachyeres patachonicus), and three flightless species: Tachyeres brachypterus (coasts of Falkland Islands), T. pteneres (coastal Tierra del Fuego through central Chile), and T. leucocephalus (coastal Chubut Province, Argentina). The protracted period required to resolve the alpha-taxonomy of the genus reflects the conspicuous characters that unit all members of the genus, and the subtle phenotypic characters that distinguish congeners (Livezey and Humphrey 1992).

See:

• Livezey, B. C. 2005. Steamer-ducks. Pp. 377-387 in Ducks, geese and swans, vol. 1 (J. Kear, ed.). Oxford Univ. Press, Oxford, U.K.
• Livezey BC. 1997. A phylogenetic classification of waterfowl (Aves: Anseriformes), including selected fossil species. Annals of Carnegie Museum 67: 457–496.
• Livezey BC, Humphrey PS. 1992. Taxonomy and identification of steamer-ducks (Anatidae: Tachyeres). University of Kansas Museum of Natural History Monograph 8: 1–125.
• Livezey BC. 1986. A phylogenetic analysis of Recent anseriform genera using morphological characters. Auk 105: 681–698.
• Livezey BC, Humphrey PS. 1986. Flightlessness in steamer-ducks (Anatidae: Tachyeres): its morphological bases and probable evolution. Evolution 40: 540–558.

Distribution and Historical Biogeography

Tachyeres is limited in distribution to the southermost “boot” of South American, with the three flightless species being mutually allopatric and the Flying Steamer-Duck (Tachyeres patachonicus) being distributed throughout this combined region as well as some Andean freshwater lakes. Phylogenetic analyses based on morphology and amino acids discriminated by electrophoresis indicate that the Flying Steamer-Duck is the sister-group of the flightess members. Within the latter, the Magellanic T. pteneres is the sister-species of the Atlantic couplet T. leucocephalus and T. brachypterus.

See:

• Livezey, B. C. 1986. Geographic variation in skeletons of Flying Steamer-Ducks (Tachyeres patachonicus). Journal of Biogeography 13: 511–525.
• Livezey, B. C. 1986. Phylogeny and historical biogeography of steamer-ducks (Anatidae: Tachyeres). Systematic Zoology 15: 454–469.

Body Form and Plumages

Subtle differences in plumage and soft parts among species, compounded by variation related to sex, age, molts and plumages, and (to a limited extent) locality, contribute to the exceptionally difficult challenges attending identification of steamer-ducks in the hand and in the field. Fortunately, in most localities these challenges are limited to the discrimination of one, comparatively large flightless species from the widespread, comparatively small flying taxon. In the Magellanic region, and especially in coastal habitats of the Falkland Islands, even this pairwise problem can prove virtually impossible under field conditions (Humphrey and Livezey ; Humphrey and Livezey 1992). Fortunately, regardless of region or taxa, the ratio between lengths of humerus and femur is sufficient for distinguishing the flying species from any flightless species. Similar ratio for wing length vs. tarsus length are less precise, primarily because of higher variances in body mass and imprecision of tarsal measurements.

See:
Livezey BC, Humphrey PS. 1984. Sexual dimorphism in continental steamer-ducks. Condor 86: 368–377.

Habitat, Feeding Ecology, and Reproduction

See:

• Humphrey PS, Livezey BC. 1985. Nest, eggs, and downy young of the White-headed Flightless Steamer-Duck. Ornithological Monograph 36: 949–954.
• Livezey BC, Humphrey PS. 1989. Feeding morphology, foraging behavior, and foods of steamer-ducks (Anatidae: Tachyeres). University of Kansas Museum of Natural History Occasional Paper 126: 1–41.

Flight and Other Modes of Locomotion

See:

• Humphrey PS, Livezey BC. 1982. Flightlessness in Flying Steamer-Ducks. Auk 99: 368–372.
• Livezey BC, Humphrey PS. 1982. Escape behaviour of steamer-ducks. Wildfowl 33: 12–16.
• Livezey BC, Humphrey PS. 1983. Mechanics of steaming in steamer-ducks. Auk 100: 485–488.
• Livezey BC, Humphrey PS. 1984. Diving behaviour of steamer-ducks Tachyeres. Ibis 126: 257–260.

Territoriality and Aggression

See:

• Livezey BC, Humphrey PS. 1985. Territoriality and interspecific aggression in steamer-ducks. Condor 57: 154–157.
• Livezey BC, Humphrey PS. 1985. [Commentary.] Condor 87: 567–568.

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