The Mauritius sheldgoose (Alopochen mauritiana), also known as the Mauritius shelduck, is an extinct species of sheldgoose that was endemic to the island of Mauritius. While geese were mentioned by visitors to Mauritius in the 17th century, few details were provided by these accounts. In 1893, a carpometacarpus wing-bone and a pelvis from the Mare aux Songes swamp were used to name a new species of comb duck, Sarcidiornis mauritianus. These bones were connected to the contemporary accounts of geese and later determined to belong to a species related to the Egyptian goose and placed in the sheldgoose genus Alopochen. The Mauritius and Réunion sheldgoose may have descended from Egyptian geese that colonised the Mascarene Islands. One contemporary account states that the Mauritius sheldgoose had wings that were half black and half white, and that the bird was not very large. The species may also be depicted in one illustration. Fossil elements show that it was smaller than the Egyptian goose, but with more robust legs. Little is known about the habits of the Mauritius sheldgoose, accounts indicate they were very tame, were grazers, lived in groups, and usually stayed on the north side of the island except for during the dry season when they were forced to the other side to drink. Their robust legs indicate they were becoming more terrestrial, which is supported by accounts stating they avoided water. The species was considered highly palatable by travellers, and while abundant in 1681, it declined quickly thereafter, being declared extinct in 1698. It was probably driven to extinction due to overhunting and predation by introduced animals, particularly cats.
Taxonomy Geese were reported by visitors to the Mascarene island of Mauritius in the 17th century, but few details were provided by these accounts. In 1889, the Mauritius government requested exploration of the Mare aux Songes swamp for "historical souvenirs", where vast amounts of dodo remains had earlier been found. The new excavations, under the direction of the French naturalist Théodore Sauzier, were successful, and apart from dodo bones, subfossil remains of other extinct animals, previously known as well as new species, were found. These bones were sent to the Cambridge Museum, where they were examined and described by the British ornithologist Edward Newton and the German ornithologist Hans Gadow in 1893. Based on a left carpometacarpus wing-bone (part of the hand, and the holotype specimen), they determined the existence of a large member of the comb duck genus Sarcidiornis, which they considered a new species due to having been restricted to Mauritius, naming it S. mauritianus. They also considered the incomplete left half of a pelvis to belong to this species. Because the contemporary accounts of geese on Mauritius did not mention a caruncle (or knob) on their bill as is seen in Sarcidiornis comb geese, the French zoologist Emile Oustalet doubted they belonged in that genus in 1896. When describing the Malagasy sheldgoose (then Chenalopex sirabensis, now in the genus Alopochen) based on fossils from Madagascar in 1897, the British palaeontologist Charles William Andrews suggested that when more remains were discovered of the Mauritian species, the two might turn out to be the same. While the British zoologist Walter Rothschild noted Oustalet's objection to the species belonging in Sarcidiornis In 1907, he believed that it was merely an oversight that the caruncle was not mentioned in contemporary accounts, and that an allusion to the small size of these geese supported them being Sarcidiornis. The American ornithologist James Greenway listed the bird as a species of Sarcidiornis in 1967.
In 1987, the British ornithologist Graham S. Cowles stated that an additional carpometacarpus from the Mare aux Songes then recently identified in the British Museum of Natural History confirmed Andrews' suggestion that the Mauritius bird did not belong in Sarcidiornis, but in the sheldgoose (or shelduck) genus Alopochen, to which the extant Egyptian goose (A. aegyptiaca) belonged. In his 1994 description of the Réunion sheldgoose (then Mascarenachen kervazoi) based on fossils from Réunion, Cowles again listed the Mauritius bird as A. mauritiana, noting that Andrews had implied it was close to the Malagasy sheldgoose. In 1997, the British ornithologists Hywel Glyn Young, Simon J. Tonge, and Julian P. Hume reviewed extinct wildfowl, and noted that the interrelationships of the four extinct sheldgeese from the region of Madagascar and the western Indian Ocean were unclear, and that they may not all have been full species. They also listed the Mauritius sheldgoose as a species of Alopochen. The French palaeontologist Cécile Mourer-Chauviré and colleagues stated in 1999 that while the Mauritius sheldgoose was similar to the Malagasy and Réunion sheldgeese, it may have been endemic to Mauritius, and may be distinguishable from those species if more remains of it are found. They also moved the Réunion sheldgoose to the same genus as the Egyptian goose and the Mauritius sheldgoose, Alophochen. The British writer Errol Fuller stated in 2000 that while the geese seen on Mauritius by 17th century travellers may be connected to the species described from bones, it is possible that there is no connection. The British ecologist Anthony S. Cheke and Hume suggested in 2008 that the Mascarene sheldgeese were derived from Malagasy forms with African affinities, probably descended from the Egyptian goose after it had colonised the Mascarene islands. They added that fossils of the Mauritius sheldgoose were "extremely rare". In 2013, Hume noted that the first known tarsometatarsus (a lower leg bone) of the Mauritius sheldgoose was collected from the Mare aux Songes in 2006, and that he had reidentified a radius (a forelimb bone) as that of the sheldgoose, which had originally been assigned to the Mauritius night heron by Newton and Gadow in 1893. Reflecting changing historical classifications and definitions, the Mauritius sheldgoose has also been referred to by common names such as Mauritius shelduck and Mascarene swan, with further variations such as Mauritian shelduck and Mascarene sheldgoose.
Description The best contemporary description of the Mauritius sheldgoose, and the only one that indicates what it looked like, is that of the English traveller John Marshall from 1668:
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