The kaki (black stilt Himantopus novaezelandiae) is one of the rarest wading birds in the world.
Previously widespread in braided rivers and wetlands throughout New Zealand, breeding is now confined to the Upper Waitaki Basin.
An intensive recovery programme managed by the Department of Conservation in Twizel has increased the population size from approximately 23 adults in 1981 to 102 adults (87 wild and 15 captive) in 2007.
However, kaki are at risk of extinction due to introduced predators, widespread habitat loss, and hybridisation with poaka (pied stilt Himantopus himantopus leucocephalus).
Below: Young kaki have black and white plumage until 18 months old. They then become all black. Photo: Loralee Hyde
A research team including scientists from Landcare Research and Canterbury and Otago universities aims to develop a framework for identifying and conserving genetic diversity in threatened species to reduce the risk of further genetic loss and species extinction.
Neil Gemmell from Canterbury University says the team chose kaki as one species to study as there is considerable data available from the Kaki Recovery Group led by the Department of Conservation.
‘Kaki evolved in isolation in New Zealand for about one million years and are different from poaka which arrived from Australia in the early 1800s.
'Kaki and poaka have different plumage and behavioural differences. For example, kaki are non-migratory,’ says Neil.
Kaki-poaka hybrids were first recorded in the late 1800s and are described by plumage variation. Kaki are pure black whereas hybrids have some white.
A species is a group of interbreeding populations reproductively isolated from such other groups.
Hybridisation occurs when individuals from different species inbreed. It is particularly common in some of New Zealand’s endangered bird species.
Hybridisation is an important evolutionary mechanism. It can either be natural or human-induced.
Tammy Steeves, also from Canterbury University, says the study is developing genetic tests to determine if there are any genetically pure kaki remaining and to establish the genetic status of hybrids.
‘We can then look at conservation implications for managing kaki and hybrids.’
The team uses DNA collected from feather samples.
‘There are two types of DNA – one from the mother and father, and the other from the mother only,’ says Tammy.
‘We are looking at both types of DNA markers to determine how many genetic groups there are.
'The key result so far is that there are two. It’s very clear pure kaki are in one group. The other group has poaka DNA.’
Orange denotes birds with kaki maternal DNA (e.g. all node J birds have kaki maternal DNA).
Blue denotes birds with poaka maternal DNA (e.g. all A-C2 birds have poaka maternal DNA).
Orange and blue denotes birds with either kaki or poaka DNA (e.g. some node I birds have kaki maternal DNA whereas others have poaka maternal DNA).
Tammy says the research is lending support to Kaki Recovery Group management decisions. ‘In the early ‘90s, dark hybrids were managed as kaki.
'In 1998, genetic work showed some of these birds had poaka DNA and it was decided to no longer manage them as kaki.
'With the DNA results so far we know this management decision was valid and it’s best to concentrate conservation efforts on pure kaki.’
Neil adds that the kaki is a good model for the drivers of hybridisation and how it influences survival rates and population dynamics.
‘This is an iconic species for conservation in New Zealand.’
Open SpaceTM Magazine No. 71, November 2007 © QEII National Trust