April 15, 2024

I, Science

The science magazine of Imperial College

Emilia Griffin tells a story of drama and hope on the conservation of New Zealand's native bird, the kākāpō.

(By Emilia Griffin on 12th January 2024)

Imagine a forest, full of colour and sound. But as the darkness of night fills the gaps between the trees, the symphony changes. The bats start squeaking, the whispering of leaves brushing together loudens, and the songbirds calm. A foghorn booms through the valley. After several booms, a metallic ching is heard in the vegetation. The moss starts to move. That moss is the speckled green feathers of the largest parrot in the world hoping to get lucky with a mate.

These noisy calls are the lek behaviour of the kākāpō. Lekking is common in the animal world amongst species which do not bond for life, but the kākāpō is the only parrot observed to do it. A lek is a territorial display at a specific site where males compete with each other to be the most attractive so that they can mate and pass on their genes. Male kākāpōs have individual lek sites where they dig a shallow bowl in the ground to louden the booming of their calls through the forest. They make many booming calls by inflating their thoracic sac, shortly followed by a metallic “ching”. Females will move to the calls they find most attractive and usually mate with them.

“Kohitatea” Strigops habroptilus (Kākāpō)
Standing awkwardly in a tree, on Codfish Island / Whenua Hou, New Zealand. (Flickr photo by Jake Osborne)

Along with their interesting mating behaviour, kākāpō exhibit some other unusual traits. They are the largest and only flightless parrot in the world. They are also nocturnal and have moss-green speckled feathers to remain camouflaged from aerial predators. Breeding events are few and far between occurring only every 2-5 years when the rimu fruit is ripe – a key source of their diet. When they do breed, only a few chicks are born in each clutch. It is thought that they reach sexual maturity after adolescence and can live for up to 90 years. This is somewhat like humans and is called a slow life history – life history is essentially the timing of events in a species and the trade-offs of energy allocation in different tasks.

Strigops habroptilus (Kākāpō)
Mother “Alice” and chick “Rupi” (formerly “Alice-A2-2022”), together in a nest cavity, on Codfish Island / Whenua Hou, New Zealand. (Flickr photo by Jake Osborne)

This is the story of the kākāpō before humans arrived in New Zealand 700 years ago. Now an oddity, the kākāpō was once among the most common birds in New Zealand. The kakapo has a strange appearance and is unable to fly, making them an easy target for humans for use as meat and clothing. Inevitably, humans brought over with them pests and predators including cats, stoats, rats and deer who posed a threat to kākāpō. Over years of predation, the numbers of kākāpō dropped dramatically.

Conservation attempts we needed desperately to try and save the kakapo from danger. The first key step in the 1980s was to relocate all individuals 3 offshore islands: Codfish Island/Whenua Hou, Maud Island and Te Hauturu-o-Toi/Little Barrier Island. However, rats made their way onto the islands and targeted nests with newly hatched chicks making it difficult for the population to keep up. By 1995, only around 50 individuals remained in existence across the islands. To overcome this the Kākāpō Recovery Programme was created with The Ngāi Tahu – the main Māori iwi (tribe) of the South Island – playing an important part in conservation since they have had important cultural and spiritual associations with the kākāpō since their early arrival to New Zealand. A key step was to eradicate all stoats, cats and rats from the islands. However, the now tiny population exhibited low genetic diversity, eventually passing through a genetic bottleneck where all individuals were closely related. Inbreeding occurred increasing infertility and susceptibility to disease. This aspect of the population declines with far apart breeding events made it difficult to increase their numbers.

An essential part of the programme has been supplementary feeding. Since the kākāpōbreeds when the rimu tree fruits, researchers have found that it is not regular enough to provide a predictable food source. This causes fewer breeding events and fewer chicks who survive. Conservationists found that by putting out supplementary food, they could try to induce breeding and therefore increase breeding success. However, they ran into a problem. It appeared that supplementary feeding resulted in an imbalanced sex ratio of chicks being born. Sex allocation theory tells us that when a mother is in better condition, she is more likely to produce the larger, sex that requires more investment – in this case, the male. It seems contradictory, but improving the health of the mother kākāpō this much was actually worse for population growth. To overcome this, researchers realised that there was a certain weight threshold where mothers would produce more male offspring. Supplementary feeding was adjusted to reach the 1.5kg threshold where mothers were healthy enough to reproduce but not so heavy that we would see an imbalance of male and female chicks. This was the first study of its kind to manipulate chick sex ratios by altering maternal condition showing that understanding life history traits and evolution theory is important for conservation.

“Sinbad”, Strigops habroptilus (Kākāpō)
at a feed station, on Codfish Island / Whenua Hou, New Zealand. (Flickr photo by Jake Osborne)

A more recent part of the programme has been Kākāpō 125+ which aims to sequence the genomes of all living kākāpō since 2015 in order to manage genetic diversity. Breeding attempts can be tracked to check whether a female has chosen a suitable partner and if she made a bad choice, artificial semination can be done to intervene.  To maintain conservation efforts on the predator-free islands, other techniques are needed. There are tight restrictions regarding transport to the islands to reduce the chance of any pests sneaking on. Since nests are regularly monitored, scientists will quickly know if any pests have made it over the seas and traps can be set out to remove them. Each year, the birds have radio transmitter trackers checked over as well as health checks and sample collection. In some cases, artificial incubation and hand rearing are necessary if a chick is unwell or a mother has had too many chicks to raise herself. The chick is returned to the wild after four months.

Sometimes, individuals will find it difficult to return to the wild due to imprinting. This is likely what happened with the famed bird, Sirocco. Imprinting happens when a chick forms a strong attachment with their mother but if the first animal or even object they see is not their mother, they may form an attachment with that instead. If they form an attachment to a human, it might mean they cannot live in the wild. Sirocco was the first kākāpō to be hand reared and since he was unwell it had to intensive which might have caused him to imprint on humans. These days he is something of a superstar deemed the “Official Spokesbird for Conservation”. Sirocco has been on tour, providing New Zealanders a chance to encounter a rare species and became globally famous after a frisky encounter with Mark Carwardine and Stephen Fry.  

These conservation efforts have lead to a population increase up to around 250 individuals, but space for lekking territory is running out on the predator-free islands. As a result, new habitat with low management is needed for a sustainable future of the kākāpō. At the moment, finding safe locations is difficult but, with the goal of a Predator Free 2050 New Zealand, native species like the kākāpō might soon thrive in a safe habitat. Things are moving in the right direction to allow for this. In July 2023, 4 male birds were translocated to the mainland in an experimental area with pest-proof fencing. The site at Sanctuary Mountain Maungatautari will host a male-only population of individuals with genes already well represented on the island. This provides an experimental opportunity to see whether this kind of habitat could work for a breeding population. This step is a hopeful promise that the acknowledgement of evolutionary theories in conservation could one day restore that long ago symphony of the forest.

Feature photo titled: “Cascade” Strigops habroptilus (Kākāpō)
Formerly Marian-A2-2022. Recently fledged. On Anchor Island / Pukenui, Dusky Sound / Tamatea, Fiordland, New Zealand. (Flickr photo by Jake Osborne)