Not an ex-parrot

ONE of the problems suffered by a species on the brink of extinction is low genetic diversity. Initially this is caused by lack of numbers, but then it is exacerbated by the inbreeding which inevitably results. Inbreeding brings with it infertility and susceptibility to disease. Hence concern for the kakapo, a nocturnal parrot that lives in New Zealand. Like many other island-dwelling birds, it has become flightless. It is also, at up to 4kg, the world’s heaviest parrot. Both of these things make it an attractive target for predatory mammals, which thankfully were absent for most of the 80m years during which it and its ancestors have inhabited the archipelago.

The kakapo’s downfall began with New Zealand’s first wave of human colonisation, some 700 years ago, by Polynesians. These arrivals hunted it, and also brought rats with them, which ate nestling chicks. The second, European wave of immigrants brought cats and stoats to add to the birds’ woes. Humans also destroyed much of their habitat to make way for crops. Conservation efforts are not assisted by the birds’ reproductive habits. They feed their chicks on the fruit of the rimu, a tree that produces its nutrient-rich morsels only every two or three years. These trees all fruit simultaneously during what are known as mast years. This means the kakapo can breed only during mast years.

With all these strikes against them it is little surprise that by the early 1970s the kakapo was thought to be extinct. But then two remnant groups were found in the south of the country. These were relocated and now live on three small, predator-free islands. After a troubled start, which saw the population hit a low of 51, this recovery programme has raised it to 123 adults.

That is still a pretty parlous state of affairs, though. So the bird’s guardians at the Kakapo Recovery Programme, run by New Zealand’s Department of Conservation, have come up with a plan they hope will put the parrot on a more secure footing, by reducing, as far as possible, the risks inbreeding brings.

According to Andrew Digby, the programme’s scientist, about half the eggs laid by female kakapo are unviable. One reason for this is a high rate of sperm abnormality, meaning many males that mate never produce offspring. The recovery team recently announced a plan to deal with this, called Kakapo 125 (then the number of adults alive; two have subsequently died). Kakapo 125 is a genome-sequencing project organised by Bruce Robertson of Otago University. Unlike other such species-specific genome projects, this one will not look merely at the DNA of a few representative individuals. Instead, it will sequence the genomes of every living kakapo—and also, if funds allow, of museum specimens too.

Isles of the blessed

Kakapo 125’s goal is to identify the genetic bases for infertility and disease. The kakapo are probably the world’s most intensively managed species. (Conservationists even sleep near their nests so they can keep eggs warm if the females wander off for too long, triggering an alarm in the process.) Hence there is a wealth of information about each individual’s health and fertility with which to correlate and interpret the genetic information. The results should help decide which male-female pairings will produce chicks with a genetic heritage that makes them as disease-resistant and fertile as possible.

Controlling who mates with whom would be a simple matter if the birds could be bred in captivity, but captive kakapo fail to thrive. Instead, that must somehow be done in the wild.

Kakapo mating is theatrical. Uniquely for parrots, they are lek-breeders. This means that the males advertise their eligibility in competitive displays for choosy females. Males scrape bowl-shaped depressions in the ground on a hilltop. Over subsequent nights they sit in or near their bowls, inflate specialised air sacs, and emit deep booms. Females, attracted by the serenades, approach the bowls along tracks the males have prepared by clearing and trimming the vegetation. An interested female may stop and mate with a male. An uninterested one will move on to appraise another suitor.

The recovery team already intervenes in this process. Each adult kakapo wears sensors that transmit information about its behaviour to members of the team. If these sensors show that a female has mated with a suboptimal male, she can, over the course of the next few days, be inseminated artificially with sperm from a more advantageous partner. (The resulting competition between sperm inside the female’s reproductive tract is usually won by those from the last mating. This phenomenon, quite common in birds, is known as last-male sperm precedence.) The recovery team do this using information from mating records and simple genetic markers. They also do it if a female has mated only once, because multiple matings boost the chance of fertile eggs.

This year is a rimu mast year, and a particularly abundant one. The breeding season reflects that abundance. At least 120 eggs have been laid. How many will hatch remains to be seen. But by the time the next such season comes around the genetic information garnered by Kakapo 125 will be available. Not a moment too soon. The oldest birds—those which have survived from the collecting expeditions of the 1970s—are starting to die. Such old-timers are likely to have the greatest diversity of all, and the most valuable genetic treasure to pass on to future generations. Knowing these birds’ genomes will permit the recovery team to take maximum advantage of whatever time these creatures have left.