This chestnut brown duck is confusable only with the fulvous whistling duck (D. bicolor) but has chestnut upper-tail coverts unlike the creamy white in the latter.
The level of monogamy varies within the family; many of the smaller ducks only maintain the bond for a single season and find a new partner the following year, whereas the larger swans, geese and some of the more territorial ducks maintain pair bonds over a number of years, and even for life in some species.
Usually placed with the dabbling ducks (Anatinae), this species may actually be closer to shelducks and belong in the subfamily Tadorninae; its closest relative is possibly the maned duck.
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The Hawaiian duck's population is affected by habitat loss, modifications to wetland habitats for flood control, non-native invasive plants, diseases, environmental contaminants, hunting and predation.
They do not walk as well on land as the dabbling ducks because their legs tend to be placed further back on their bodies to help propel them when underwater.
Any long-term decrease in the duck’s population would therefore be caused by habitat loss through factors such as salinity and overgrazing more so than drought.
Since 1600, five species of ducks have become extinct due to the activities of humans, and subfossil remains have shown that humans caused numerous extinctions in prehistory.
On the other hand, Streets' reports suggest that there was a population of these ducks of some size present, and thus they may have lived there since quite some time and indeed be worthy of recognition as a distinct taxon.
It was then reinstated in its own genus and moved to the shelduck subfamily Tadorninae, which also contains the torrent duck and blue duck which convergently have evolved adaptations to mountain stream habitat.