As a land without terrestrial mammals of any kind, New Zealand was, until the arrival of the first humans, inhabited by an extraordinarily diverse range of specialised birds. The ecological niches occupied by mammals as different as cows and rodents, kangaroos and moles, were filled by reptiles, insects, or birds.

When humans arrived in New Zealand sometime between 800 and 1300, this unique and unusual ecology was endangered. Several species were hunted to extinction, most notably the moa and harpagornis. The most damage however was caused by the other animals that humans brought with them, particularly rats (both the Polynesian rat or kiore imported by Maori and the Norwegian rat subsequently introduced by the Europeans), but also dogs, cats, stoats, weasels, hedgehogs, and, the Australian possum. The flightless birds were in particular danger.

The 49 species marked extinc became extinct subsequent to man's arrival in New Zealand. Of these, 34 extinctions occurred after the arrival of Maori but before the arrival of Pakeha with 15 further extinctions since and others remain critically endangered. Several species are now confined only to offshore islands, or to fenced "mainland islands" from which predators have been eliminated. Consequently New Zealand is today a world leader in the techniques required to bring severely endangered species back from the brink of extinction.

In 1840 when the first European settlers arrived in New Zealand the endemic NZ Brown Teal was possibly the country's most abundant species of waterfowl. It was found in every swamp and wetland, many riverine systems, and in very large numbers in both the North and South Islands of New Zealand. Large numbers were also found on Stewart Island and on the Chatham Islands.

In 1882 Buller wrote "this elegant little duck is distributed all over the country, being met with in every inland lake and often in the deep freshwater streams which run into them, where the overhanging vegetation affords ready shelter and concealment". Such a statement can only make the species' decline a more spectacular disaster.

The widespread distribution, and the spectacular decline, has been confirmed by research into the fossil distribution of Brown Teal. Data in this research show that there was often no direct association between Brown Teal fossils in forest sites and aquatic habitat, such as ponds or rivers, and that Brown Teal were often foraging in forests some considerable distance from wetlands. The Brown Teal fossil sites found in this research confirms the historic abundance of Brown Teal and their widespread usage of lakes, swamps, kahikatea swamps, in high mountainous areas and in many coastal areas.

Fossil remains have been found throughout the North and South islands and indicate that the Brown Teal population was large and that the species has been in existence for over 10,000 years.

No estimate of population size appears to have been recorded, but putting all available evidence together it can be assumed that historically the total population would have numbered in the millions. Such a population of Brown Teal is reminiscent of the New Zealand mallard population today.

Capt Cook first wrote about Brown Teal in 1838 and there is compelling evidence that both Maori and European hunters killed them in very large numbers.

Until the early 1900's it was in fact only duck hunters who really showed any interest in Brown Teal - rather perversely, duck hunters found Brown Teal to be a fine game bird; they flew well, decoyed well and were a tasty table bird.

In the South Island the presence of Brown Teal was, until recently, not so well recorded, but records do show an abundance on Stewart Island, along the West Coast, in Canterbury and in Marlborough.

Research completed in 2002 confirms that Brown Teal populations were far more widespread than previously thought and that Brown Teal were also present in the once vast wetlands of Southland and throughout the once extensive Otago wetlands.

During the late 1800's and early 1900's Brown Teal numbers began to decline quite rapidly; due largely to the impact and abundance of introduced predators, such as mustelids, hedgehogs and feral cats. Excessive shooting, long after Brown Teal became protected in 1921, also helped the dramatic decline, as did the massive and dramatic drainage of wetlands, and the destruction of native forests. Over 90% of New Zealand's wetlands were lost and over 70% of native forests were destroyed.

But there is now clear and conclusive evidence that feral cats, rats and mustelids have perhaps played the biggest part in the decline.

As already mentioned, the fossil research shows that the Brown Teal population was large and that the species has been in existence for over 10,000 years.

In 2002 total Brown Teal numbers in the wild were down to approximately 1,000 and there is now an urgent need to turn the decline around.