The huia was found throughout the North Island before humans arrived in New Zealand.
Māori are estimated to have arrived around 750 years ago, and by the arrival of European settlers in the 1840s, habitat destruction, hunting, and introduced rats had reduced the bird's range to the southern North Island.
However, Māori hunting pressures on the huia were limited to some extent by traditional protocols.
The hunting season was from May to July when the bird's plumage was in prime condition, while a rāhui (hunting ban) was enforced in spring and summer.
After European settlement the huia's numbers began to decline more quickly, due mainly to two well-documented factors: widespread deforestation and over-hunting.

Like the extinctions of other New Zealand birds such as the piopio in the 19th century, the decline of the huia was poorly studied.
Massive deforestation occurred in the North Island at this time, particularly in the lowlands of southern Hawkes Bay, the Manawatu and the Wairarapa, as land was cleared by European settlers for agriculture.
The huia was particularly vulnerable to this as it could only live in old-growth forest where there were abundant rotting trees filled with wood-boring insect larvae.
It seems it could not survive in regenerating, secondary forests.
Although the mountainous part of its former range was not deforested, the lowland forests of the valleys below were systematically destroyed.
The destruction of this part of its habitat would have undoubtedly had a severe impact on huia populations, but its removal would have been particularly dire if they did in fact descend to the lowlands as a winter refuge to escape snow at higher altitudes as some researchers including Oliver have surmised.

It appears that predation by invasive mammalian species including ship rats, cats, and mustelids was an additional factor in the decline in huia numbers – introduction of these animals by New Zealand acclimatisation societies peaked in the 1880s and coincided with a particularly sharp decline in huia populations.
Because it spent a lot of time on the ground, the huia would have been particularly vulnerable to mammalian predators.
Another hypothetical cause of extinction is exotic parasites and disease introduced from Asia with the common myna.

Habitat destruction and the predations of introduced species were problems faced by all New Zealand birds, but in addition the huia faced massive pressure from hunting.
Due to its pronounced sexual dimorphism and its beauty, huia were sought after as mounted specimens by wealthy collectors in Europe and by museums all over the world.
These individuals and institutions were willing to pay large sums of money for good specimens, and the overseas demand created a strong financial incentive for hunters in New Zealand.
This hunting was initially by naturalists.
Austrian taxidermist Andreas Reischek took 212 pairs as specimens for the natural history museum in Vienna over a period of 10 years, while New Zealand ornithologist Walter Buller collected 18 on just one of several expeditions to the Rimutaka Ranges in 1883.
Others keen to profit soon joined in.
Buller records that also in 1883, a party of 11 Māori obtained 646 huia skins from the forest between the Manawatu Gorge and Ākitio.
Several thousand huia were exported overseas as part of this trade.
Infrastructure development within lowland forest did not help the situation: hundreds of huia were shot around road and rail construction camps.

While we were looking at and admiring this little picture of bird-life, a pair of Huia, without uttering a sound, appeared in a tree overhead, and as they were caressing each other with their beautiful bills, a charge of No.
 6 brought them both to the ground together.
The incident was rather touching and I felt almost glad that the shot was not mine, although by no means loth to appropriate 2 fine specimens.

— Sir Walter Buller, New Zealand's well-known 19th-century ornithologist, encapsulating what one source describes as the "ambiguous" 19th-century attitudes towards the declining New Zea
The huia was found throughout the North Island before humans arrived in New Zealand. Māori are estimated to have arrived around 750 years ago, and by the arrival of European settlers in the 1840s, habitat destruction, hunting, and introduced rats had reduced the bird's range to the southern North Island. However, Māori hunting pressures on the huia were limited to some extent by traditional protocols. The hunting season was from May to July when the bird's plumage was in prime condition, while a rāhui (hunting ban) was enforced in spring and summer. After European settlement the huia's numbers began to decline more quickly, due mainly to two well-documented factors: widespread deforestation and over-hunting.
Like the extinctions of other New Zealand birds such as the piopio in the 19th century, the decline of the huia was poorly studied. Massive deforestation occurred in the North Island at this time, particularly in the lowlands of southern Hawkes Bay, the Manawatu and the Wairarapa, as land was cleared by European settlers for agriculture. The huia was particularly vulnerable to this as it could only live in old-growth forest where there were abundant rotting trees filled with wood-boring insect larvae. It seems it could not survive in regenerating, secondary forests. Although the mountainous part of its former range was not deforested, the lowland forests of the valleys below were systematically destroyed. The destruction of this part of its habitat would have undoubtedly had a severe impact on huia populations, but its removal would have been particularly dire if they did in fact descend to the lowlands as a winter refuge to escape snow at higher altitudes as some researchers including Oliver have surmised.
It appears that predation by invasive mammalian species including ship rats, cats, and mustelids was an additional factor in the decline in huia numbers – introduction of these animals by New Zealand acclimatisation societies peaked in the 1880s and coincided with a particularly sharp decline in huia populations. Because it spent a lot of time on the ground, the huia would have been particularly vulnerable to mammalian predators. Another hypothetical cause of extinction is exotic parasites and disease introduced from Asia with the common myna.
Habitat destruction and the predations of introduced species were problems faced by all New Zealand birds, but in addition the huia faced massive pressure from hunting. Due to its pronounced sexual dimorphism and its beauty, huia were sought after as mounted specimens by wealthy collectors in Europe and by museums all over the world. These individuals and institutions were willing to pay large sums of money for good specimens, and the overseas demand created a strong financial incentive for hunters in New Zealand. This hunting was initially by naturalists. Austrian taxidermist Andreas Reischek took 212 pairs as specimens for the natural history museum in Vienna over a period of 10 years, while New Zealand ornithologist Walter Buller collected 18 on just one of several expeditions to the Rimutaka Ranges in 1883. Others keen to profit soon joined in. Buller records that also in 1883, a party of 11 Māori obtained 646 huia skins from the forest between the Manawatu Gorge and Ākitio. Several thousand huia were exported overseas as part of this trade. Infrastructure development within lowland forest did not help the situation: hundreds of huia were shot around road and rail construction camps. 
While we were looking at and admiring this little picture of bird-life, a pair of Huia, without uttering a sound, appeared in a tree overhead, and as they were caressing each other with their beautiful bills, a charge of No. 6 brought them both to the ground together. The incident was rather touching and I felt almost glad that the shot was not mine, although by no means loth to appropriate 2 fine specimens.
— Sir Walter Buller, New Zealand's well-known 19th-century ornithologist, encapsulating what one source describes as the "ambiguous" 19th-century attitudes towards the declining New Zea
Huia