North Island kōkako

The North Island kōkako (Callaeas wilsoni) is a forest bird endemic to the North Island of New Zealand. It is grey in colour, with a small black mask. Adults have distinctive blue wattles. Because of its wattle, the bird is sometimes locally called the blue-wattled crow, although it is not a corvid. The name "kōkako" comes from its vocalization: the bird's main call has been described as a "slow, rich 'ko-ka-ko-o-o-o', tailing off at the end".^[3]

The North Island kōkako can be identified by its grey plumage and by a pair of blue, fleshy wattles at the base of the bill. Its overall coloration is a soft, slate-grey to smoky blue hue that envelops its entire body.^[4]

The plumage is generally uniform grey, with slightly darker colouring on the wings and tail. The feathers have a silky appearance and a very fine texture. The breast and belly are often a little paler than the back.

The face of the kōkako features a black facial mask that covers the area around the eyes and extends to the base of the bill.

The species' most notable feature is its vivid blue wattles.^[5] These wattles are typically a saturated cobalt or ultramarine blue, with subtle purple tones, and they can vary slightly in shape and size among individuals. The wattles are thought to play a role in social signaling and courtship. Juveniles have pink or lilac wattles, which become increasingly blue as the bird matures; like the South Island kōkako, adults occasionally have orange wattles.^[6] The wattles also play a role in thermoregulation, as they help dissipate body heat on hot days and retain heat in colder climates. When the bird is warm, blood flow to the wattles increases, allowing heat to escape. When it is cold, blood flow decreases, helping to preserve body warmth. Furthermore, the wattles can indicate an individual bird's health.

The bill is relatively short and curves slightly downward; it is black in color and sturdy, and is suited to the bird's omnivorous diet of fruits, leaves, and invertebrates.

The legs and feet are strong and built for agility among tree branches, and they are bluish-grey to black in colour. Kōkako are not strong fliers;^[7] instead, they are highly adapted for climbing and leaping through the forest canopy, using their powerful legs and claws to move through the dense foliage.

The North Island kōkako is a medium-sized bird, measuring about 38 to 40 centimeters (15 to 16 inches) in length,^[8] including a long, rounded tail that aids in balance and maneuverability. The tail feathers are dark and broad, and are often fanned out slightly when the bird is climbing or displaying.

Sexual dimorphism is minimal, though males tend to be slightly larger.

In the early 1900s the North Island kōkako was common in forests throughout the North Island and its offshore islands. The primary causes of its decline were forest clearance by settlers and the introduction of predators such as rats, stoats and possums.

Unlike many of New Zealand's most vulnerable birds, kōkako survive in low numbers in several North Island native forests. However, research has shown that female kōkako are particularly at risk of predation as they carry out all incubation and brooding throughout a prolonged (50-day) nesting period. Years of such predation have resulted in populations that are predominantly male, with consequent low productivity rates.^[9]

Government-funded pest control programmes, and captive breeding programmes are critical to helping maintain population numbers on the mainland. A "research by management" approach has demonstrated that the kōkako decline can be reversed and populations maintained in mainland forests by innovative management of their habitat. Current research aims to increase management efficiency to ensure long-term kōkako survival. The use of biodegradable 1080 poison has been particularly beneficial in reversing population decline. For example, between 1991 and 1999 the breeding population of kōkako increased tenfold in Mapara Wildlife Reserve (Waikato) thanks to a series of four aerial 1080 operations.^[10] A population of kōkako has also been re-established at the Otanewainuku Forest^[11] in the Bay of Plenty.^[12]

New populations are also being established through releases on predator-free offshore islands. As a result, conservationists are hopeful for the species' long-term survival. As of 2022, the IUCN no longer considers the kōkako to be threatened and has been moved to the designation of Least Concern, although the species is still heavily dependent on conservation efforts.^[13] It is still considered a threatened species by New Zealand authorities, however.^[2]

As of 2010, North Island kōkako were present in Pureora Forest Park,^[14] Whirinaki Te Pua-a-Tāne Conservation Park,^[15] Mapara Wildlife Reserve,^[16] the Hunua Ranges,^[17] Ngapukeriki,^[18] Kaharoa Forest,^[19] the Te Urewera National Park,^[20] Puketi Forest,^[21] the Waitākere Ranges^[22] and Waipoua Forest^[23] in Northland. Kōkako can be seen easily on a number of publicly accessible offshore island sanctuaries, including Tiritiri Matangi and Kapiti Island, where the regenerating forest is low enough to provide close views.