New Zealand native birds have been greatly affected by predation. For millions of years, they lived in an environment without natural predators. Many species developed traits like flightlessness, lack of defence behaviours, and ground-feeding and ground-dwelling behaviours. They were easy prey when humans and introduced predators arrived.
Adaptations such as colouration and nocturnal behaviour weren’t enough to protect the birds, as many new predators hunted by smell. Nearly a third of native bird species breeding in prehuman times in New Zealand became locally or globally extinct after human arrival.
Human settlement and its effect on bird populations
The first Māori settlers brought with them the Polynesian rat (kiore), which grew in abundance due to a landscape rich in food. Whakataukī (Māori proverbs) suggest that kiore were an important aspect of Māori culture and provided a good source of protein. New Zealand birds were poorly adapted to withstand attacks from these rats. The kiore was a proficient climber, taking the eggs and chicks of birds nesting in trees.
Māori used feathers particularly from kiwi, kererū and kākā to make cloaks. Feather cloaks signified a person of high ranking or were used for trading goods. Feathers were also used to adorn spearheads, waka and kites. Bones from the birds were used to make hairpins or tools for weaving or fishing.
Native birds were also a rich food source for Māori. Kererū feature strongly in Māori myths, legends and waiata. Kererū were considered a delicacy, especially if the birds had fed on the fruit of the miro tree, as the juices of the berry made them tender to eat. They were often caught with a noose or snare that had been set up near a source of water as they came down to drink. Spears were also used to catch the birds.
Laws evolved surrounding the use of kererū as a food source – Māori hunters would only take what was required to ensure there were sufficient birds remaining to breed for the next season.
With the later arrival of European settlers, other animals were introduced. The ship rat and the Norway rat escaped from the boats of these explorers and were even more destructive than the kiore. These rats thrived in New Zealand. Flightless birds became ideal prey for cats, rats and dogs. The later introduction of possums and mustelids (weasels, stoats and ferrets) has had a devastating effect on native birds.
The effects of predation
Possums affect native birds by damaging the forest canopy, resulting in birds competing with these predators for food. Possums have also been filmed taking and eating chicks and eggs from nests in the night. Ship rats in particular are well adapted to an arboreal lifestyle and can easily climb trees to feast on chicks and eggs. Interference by predators can cause birds to desert their nests, cause damage to eggs and lead to the possibility of eggs and chicks falling out of nests.
Ground-dwelling birds like young kiwi and takahē are also at risk of predation. Eggs and chicks are often exposed to predators while the male or female parent goes in search of food. A kiwi chick is not strong enough to fight off possible predators until it reaches approximately 800–1000 grams. This is the approximate weight that crèche sites get kiwi up to before they are released into sanctuaries.
Mammalian predators continue to threaten numbers of native birds, and conservation programmes are required to protect populations of these endangered birds. In areas that have undergone predator control, birds have had greater nesting success, less predation at nests and a larger breeding population.
The Pest Detective website provides an online guide to help identify the signs left by pest animals.