KAKA A Threatened Species?

Forest and Bird, Issue 250, 1 November 1988, Page 18

KAKA A Threatened Species?

by

and

Jacqueline Beggs

Peter Wilson

cientists are worried that South Island kaka are not breeding successfully. An intensive four-year study on kaka in the Nelson Lakes region found only three nests, and the eggs in all three failed to hatch. A separate study on birds in South Westland also found that the kaka there were not breeding. The kaka is a forest-dwelling parrot. It is closely related to the alpine kea, although it is not seen as often as the kea because it spends most of its time in the tops of trees. There are two subspecies, the North Island kaka and the larger, more brightly coloured, South Island kaka. At the time of the arrival of European settlers in New Zealand there were accounts of large flocks of kaka throughout much of the country. Indeed, Buller in 1888 reported that the kaka was one of New Zealand's ‘’. . . characteristic forms and is met with, more or less, in every part of the country."’ Today, kaka live only in the larger remaining forests, and in most of these areas they survive only in low numbers. Why did the number of kaka decline so dramatically, and how secure is their future? To try and find the answers, our DSIR Ecology Division research team studied the kaka in beech forests of the Nelson Lakes region. The destruction of forest habitat is one obvious reason for the reduced distribution of kaka, but we wanted to find out how well kaka were surviving in the areas where the forest is still intact. It would be a great shame if kaka were to become yet another species restricted to a few offshore islands or remote forests most New Zealanders will never see.

Difficult to Study

Kaka are difficult to study, as they live in the tops of trees and often move large distances. It was obvious that we would need a fairly sophisticated technique to locate and follow these birds, so with help from Brian Karl of Ecology Division we developed a method for attaching a miniature radio transmitter that would withstand the powerful ‘‘bolt cutters’ the kaka has for a beak. The transmitters were held on by a harness system, like a small daypack, and a weak link was built in so that the transmitters would eventually fall off.

Kaka spend a lot of time collecting insects, from both dead and live trees. Male kaka can spend up to two hours digging into the live wood of a mountain beech to capture one larva of the kanuka longhorn beetle. This larva looks very similar to the huhu grub, and is rich in fats and protein. However, the kaka uses so much energy to dig the larva out that not enough energy is gained from eating it to meet the bird's daily requirements. For energy, the kaka must supplement the insects with a richer, more easily accessible food. There are many anecdotal accounts of kaka feeding on fruits and nectar, but both these food sources are scarce in northern South Island beech forests. Instead, the kaka we studied fed on drops of honeydew. This is a sugary substance produced by a small scale insect which lives in the bark of some beech trees. The honeydew drops have a high energy content but a low protein content, so by themselves they are not a balanced diet. However, when the energy from honeydew is combined with the protein and minerals from insects, kaka have a diet that allows them to survive in beech forests. Kaka feed on honeydew mainly in the late afternoon and early morning. This helps them to survive through the night, and to gain energy quickly in the morning before they head off to start digging out insects. Kaka collect most of their honeydew from branches in the tree canopy. Experiments have shown that the sugar concentration in droplets from the canopy level is higher than in droplets lower down the tree. We needed to find the answers to three questions before we could calculate how much energy the kaka would get from feeding on honeydew: @ How fast can kaka collect drops of honeydew? @ What is the average energy value of a drop of honeydew? e How much energy does a kaka use up in collecting honeydew? We found that kaka could collect about three drops of honeydew every second. Each droplet had an energy value of about 11 joules. From this we estimated a kaka would only need to feed on honeydew for about three hours to get enough energy to

last it through a summer day. It should need to feed for longer in winter because of the colder temperatures, but honeydew would still be a good source of energy.

Competition from Wasps

There are two main species of introduced social wasp in New Zealand: the German wasp and the common wasp. These wasps build up to very high numbers in beech forests with honeydew trees, and hundreds of wasps can be seen crawling over each honeydew tree in late summer and autumn. The wasps take so much of the honeydew at this time of the year that there is not enough left for the kaka. Kaka are rarely seen in the honeydew areas when wasps become numerous. In its natural state, a beech forest contains very few flowering or fruiting plants. The introduction of possums and deer has reduced the variety even further. Possums, for instance, have killed many of the mistletoes you would normally expect to find in beech forests, yet kaka feed on the fruit and flowers of these plants in areas that possums have not yet reached. Now, when wasps drive the kaka away from the honeydew, there are few alternative foods for them to turn to as a source of energy. The sap of trees is one option, and kaka do feed on sap, but it is harder to get and probably not as rewarding as honeydew. It seems likely that kaka have to scratch a living from a combination of insects, sap, and seeds when they are available. Unfortunately, the worst time comes in autumn

when the birds need to build up their reserves of fat. If kaka are short of energy reserves in winter, then by spring they may not have the extra energy they need in order to breed.

Lack of Breeding

It is of great concern to us that in four years of fieldwork we have not found a single successful kaka nest. One pair we were observing attempted to breed three times, but the eggs never got any further than the incubation stage. They were all eaten by rats, but we think this happened only after the kaka had abandoned the nest. The birds stayed on the nest until well after the eggs should have hatched, but without any success. The female does all the incubating, and has food brought to her by the male, with at least one other kaka helping him. It is possible that these "‘helpers’’ at the nest are part of a family group, but information on the social organisation of kaka would take many years to collect — especially since they breed so infrequently. Colin O'Donnell and Peter Dilks of the Department of Conservation have been assessing the birdlife of forests in South Westland since 1983. They have not found any kaka breeding in their study areas. Combine this with the lack of successful nesting we have found, and the future of South Island kaka looks bleak. Nobody knows how long kaka live for, but parrots in general have a long life span. Kaka can probably live for longer than 20 years, so if a kaka population was not producing any young then it would be many years before a decline in the number of birds was noticeable. In other words, the kaka populations in some or all of our forests could be made up solely of elderly birds, and if we were only to count the number of kaka present, then we would probably not notice the problem until it was too late. The solution for kaka may lie with active management of the beech forests of North Westland, Nelson and Marlborough. The introduction of a wasp parasite may be one answer, and is currently being looked at by DSIR under contract to the Department of Conservation. It may also be necessary to provide extra food for kaka at certain times

of the year — perhaps by planting a food source that is not attractive to wasps. What is needed now is more research, aimed at finding out whether our theories about the lack of breeding are correct, and determining how widespread the problem is. It is easier to help save the kaka now, before their numbers have become critically low and we are faced with yet another endemic species requiring ‘‘emergency treatment’’. Preventative medicine is always the better option. Jacqueline Beggs and Peter Wilson are scientists working for DSIR Ecology Division in Nelson. The author's work has been part funded by recent grants from the J.S. Watson Trust and The Native Forest Restoration Trust.