Feature

Bird Voyeurs

Little is known about the breeding cycle of our native birds, but a new breeding programme may help change that.

By Cathryn Crane

Dr John Cockrem and his colleagues are going to spend the next few years examining birds intimately. They'll be watching them, tracking them, analysing their droppings. All this to find out out how native birds breed and what can be done to enhance breeding in endangered species.

As the country's only avian physiologist, Dr Cockrem is well placed in the new Reproduction and Biological Rhythms Laboratory in Massey's Department of Physiology and Anatomy. He will be using a whole battery of techniques to study breeding patterns in birds as varied as ducks, kakapo, and kiwis.

Almost all New Zealand's native birds are seasonal breeders, some taking breaks as long as five years between chicks. Scientists don't know why this should be so, nor do they understand what factors bring on a breeding phase.

Environmental factors seem to play a large role in encouraging breeding. In desert areas, periods of heavy rain can start breeding displays. Most commonly, lengthening days in early spring set many birds to look for mates and nest sites. Kiwis are a puzzling exception to this rule.

"The birds are being turned on by something in late autumn, " says Dr Cockrem, noting that such timing is most unusual for birds. He hopes that data from kiwi houses around the country may provide some clue as to the strange timing.

Keeping kiwis in captivity provides a means of controlling the day length, the feeding cycle and other environmental factors that may be involved in breeding. It also provides scientists with data on the egg-laying period, clutch sizes and the time taken to lay all the eggs within one clutch.

"If day length is important in the time of breeding, you may be able to push the birds through several reproductive cycles in one year, " Dr Cockrem notes. With kiwis on the endangered list, that could be an important discovery for its future.

Dealing with small populations of birds which cannot be removed from the wild is more difficult. Yet these birds, too, could benefit from better understanding of their breeding cycles. The small group of kakapo which were moved to Little Barrier Island for their safety took seven years to re-establish breeding patterns. If they could have been made ready for breeding earlier, then their current precarious position could have been strengthened.

It is easy to determine when kakapo males are ready for breeding. In the early summer the males begin booming to attract a mate. Their air sacs and gonads both enlarge in readiness for breeding. (Sparrows are even more extreme -- their testes increase from 0.04% to 2.8% of body weight. The human equivalent would be an increase in testes weight from 30 grams to two kilograms.)

Judging when a female bird is ready for mating is far more difficult, as there are usually no imediately obvious signs. One method of establishing reproductive readiness is to measure hormone levels in the blood. With a small population in a bush habitat, this approach is untenable. Dr Cockrem is developing a technique whereby droppings can be analysed for hormones. The birds don't have to be bothered and it is easier to get data on the entire population. However, the minute quantities of hormones involved mean that the assay techniques have to be carefully controlled.

"For the first time we can get a picture of what's happening with the female, " he says. As the egg layers, it is the females who are of greatest interest to the bird specialists.

The initial studies will be conducted on a group of grey ducks, also a native species, although not one in immediate danger. The ducks will be carefully monitored for hormone levels, environmental factors and breeding patterns. Dr Cockrem sees a number of advantages with ducks -- they have a distinct breeding season, they are large enough to be able to cope with repeated blood samples and their captivity does not raise the same concern as that of more endangered birds.

The humble ducks may provide the answers needed to help their rarer cousins, whether it's in a better understanding of how and when birds breed or in the tricky area of hormone therapy to encourage ovulation and egg laying in species on the brink of extinction.

Cathryn Crane is a freelance journalist with an interest in environmental issues.