The rank and status of the taxon is controversial because the birds possessed the traits of common ( Anas platyrhynchos ) and gray mallard ( Anas superciliosa ) - allopatric species that often form interspecific hybrids . The males of the Marian Mallard had two interconnected color morphs, called the types “platyrhynchos” and “superciliosa”, similar to the species they looked more like in their morphological characteristics. The first of the morphs was first described by Tommaso Salvadori as an independent species of the genus Anas . The species name was given in honor of the first specimen of the French zoologist Emile Ustale, who gathered it, (Jean-Frédéric Émile Oustalet 1844-1905) [1] . Salvadori suggested that the taxon is associated with gray mallard [1] [2] .
After Salvadori, most taxonomists considered the taxon to be a subspecies of the common mallard [2] [3] . In 1948, Japanese ornithologist Yamashina Yoshimaro examined samples of these birds in museums in Japan and came to the conclusion that the Marian mallard is an example of hybrid speciation and is derived from the crossing of an ordinary mallard and the Palawan subspecies of the gray mallard ( Anas superciliosa pelewensis , artlaub & 2 Finsch) ] [4] . However, there is no available molecular genetic data to support this hypothesis. Some scholars, such as the American ornithologist Jean Théodore Delacour, considered the Marian Mallard to be a simple hybrid, which is why it was absent from the four-volume monograph Delacour visited by ducks [2] .
Marian Mallards and their precursor species are not known to be fossilized in the Mariana Islands, casting doubt on the assumption that a population of gray Mallards has existed on the islands for a long time. However, most of the rocky shelters and caves where they could preserve the subfossil remains of ducks on the Mariana Islands were destroyed in the Battle of Guam in 1944 [5] . The flightless species of ducks, known for the fossil bone found on the Rota in 1994, apparently was not closely related to the Marian mallard [6] .
A relatively large, stocky river duck with a large head and short tail. Length 51-56 cm with a body weight of about 1 kg. There were two interconnected color morphs of males: - platyrhynchos and superciliosa . In the mating plumage, the platyrhynchos- shaped spleen had a dark green head and neck (less shiny than that of males of an ordinary gully), with several dark brown feathers on the sides of the head. The green field around the neck ended in a narrow white “collar”. The upper chest was dark chestnut brown or chocolate brown with blackish brown spots. Wings on top with bright blue-violet with white “mirror” borders. On the tail there was a black curl formed by the middle helmsmen. The rest of the tail feathers are straight, have a light gray color. The abdominal part of the body combined in color the brownish-gray plumage of an ordinary mallard with brown feathers, like in a gray mallard. Legs are orange-red with darker membranes. The rainbow is brown. The male superciliosa in color resembled a gray mallard drake with less distinct dark strokes on its head. The lower body was lighter. The “mirror” was usually like a Palawan subspecies of a gray mallard, at least two mined specimens had a green “mirror”, like a gray mallard. The female of the Marian Mallard resembled a dark-colored female of the ordinary form with orange legs [1] .
Endemic to the Mariana Islands in the Pacific Ocean - the species lived on only three small islands: Saipan , Tinian and Guam [7] [8] .
The Mariana mallard lived on wetlands, mainly on the interior of the islands, but was also sometimes found in coastal areas. On Guam, the species was most common in the Talofofo Valley, on Tinian - on Lake Hagoy and Lake Makpo (before it was drained and turned into a swamp of Makpo), and on Saipan - in the lagoon of Garpan and on Lake Susupe. Birds preferred water bodies with abundant aquatic vegetation - thickets of fern Acrostichum aureum and reeds Scirpus , Cyperus and Phragmites [9] [10] .
Usually birds were found in pairs or small flocks, but in the main habitats there were larger groups of up to 50-60 birds. Birds led a sedentary lifestyle. Data on diet and breeding patterns have not been investigated, but it is unlikely that they will significantly differ from similar species. The Mariana Mallard ate aquatic plants, invertebrates, and small vertebrates.
Reproduction was recorded from January to July, with a peak in June-July (at the end of the dry season). Clutch with 7-12 pale gray-green oval eggs about 6.16 x 3.89 cm in size. The incubation period lasted about 28 days, the males did not take part in incubating the eggs and did not take care of the chicks [10] [9] .
Extinction occurred due to uncontrolled hunting and drainage of wetlands for agricultural needs and construction. The number of birds decreased significantly during the Second World War . The last encounter with the Mariana mallard in the wild on Tinian was recorded in 1974 - it was a single bird. The last time on the island of Guam, Marian mallards (two males and a female) were observed in 1979, and in 1981, individuals kept in the Water World Zoo in San Diego (USA) died, where attempts to breed them were unsuccessful [11] .
