The yellowhead or mohua (Mohoua ochrocephala) is a small insectivorous passerine bird endemic to the South Island of New Zealand.

Once a common forest bird, its numbers declined drastically after the introduction of rats and stoats, and it is now near threatened.

The yellowhead was formally described in 1789 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae.

[3] Gmelin based his account on the "yellow-headed fly-catcher" that had been described in 1783 by the English ornithologist John Latham in his book A General Synopsis of Birds.

[4] The naturalist Joseph Banks had provided Latham with a watercolour painting of the bird by Georg Forster who had accompanied James Cook on his second voyage to the Pacific Ocean.

[5] The yellowhead in now one of three species placed in the genus Mohoua that was introduced in 1837 by the French naturalist René Lesson.

Although abundant in the 19th century, particularly in southern beech forests on the South Island and Stewart Island / Rakiura, mohua declined dramatically in the early 20th century due to the introduction of black rats and mustelids; nesting in tree holes makes them more vulnerable to predators.

[10] Although mohua are insectivores, they have been observed to be opportunists who can eat various food items, including nuts and dried fruits.

[12] Rimu and miro were the main foraging surfaces for mohua in the Ulva Island forest but were preferred at different rates depending on the time of year.

[12] However, during the November and December periods, mohua prefer a greater variety of species to forage from, including Rātā and Muttonbird Scrub.

[14] Like other birds, mohua weave cup-shaped nests using soft materials such as moss, grass, filmy ferns and lichens.

[15] Knot holes on tree trunks were the preferred place for mohua to build their nests.

This multi-species flocking technique will likely help with more effective foraging as more individual birds can spot abundant prey.

[13] This tree hole nesting strategy prevents the predation of mohua by long-tailed cuckoos and other carnivorous birds such as the falcons and morepork.

[18] Pest control efforts by the Department of Conservation have managed to stabilise some mainland mohua populations.

For example, where biodegradable 1080 poison was used to control rats in the Dart valley, there was a more than 80% survival rate, compared with just 10% in untreated areas.

[19] The population of mohua in the Landsborough valley has increased four-fold since 1998, thanks to an intensive programme of pest control, including aerial 1080.

[citation needed] Similar aerial 1080 operations in the Catlins[20] and the Hurunui,[21] Hawdon and Eglinton valleys[22] have had equally encouraging results.

DOC and TBfree New Zealand noted in March 2014 that there was a significant repopulation in the Catlins of other avian species, including bellbird and tomtit due to the reduction of predators.