Following extinction on the mainland, merganser survived on the bleak but beautiful Auckland Islands. The population must have started to decline after pigs were introduced to the Auckland Islands in 1807, and cats in 1820.
The failed settlement at Port Ross in 1849-1851 probably had an impact on the demise of merganser. It is quite likely that disillusioned settlers who had extreme difficulty obtaining food in the harsh conditions, hunted duck.
The flightless Auckland Island teal Anas aucklandicus has survived on Ross, Enderby, Ewing and Dundas Islands off the northeast tip of the Auckland Islands because those islands have remained free of introduced rats.
At latitude 50.5°South, the Auckland Islands are the world's third most southern duck location, behind the Campbell Islands (latitude 52.5°South), and Tierra del Fuego (latitude 54.9°South).
The world's five Mergus species
The Auckland Island merganser could be one of a small number of New Zealand birds that have been exceptional colonisations from the Northern Hemisphere. Mergus australis has its closest relative in Mergus squamatus of China (Kear & Scarlett 1970).
There are four living species of the Mergus genus worldwide. The only other species of the southern hemisphere is the Brazilian merganser M. octosetaceus which is listed as 'critically endangered' on the IUCN Red List of Threatened Species.
Three species in the northern hemisphere include the red-breasted merganser M. serrator, and common merganser M. merganser which are both migratory and listed as 'least concern'; and the very striking looking scaly-sided merganser M. squamatus of Asia which is 'endangered'.
The Auckland Island merganser was the smallest of all Mergus species, weighing less than a kilogramme, and with a torso length of (20.5 inches).