The North Island kōkako (Callaeas wilsoni) is a charismatic songbird which as its name suggests, is endemic to the North Island of New Zealand. It is perhaps most well-known for its distinctive song, which can be heard emanating through its native forest home as day begins to break. If you’ve ever been curious about which animals are hiding in your wallet you may have noticed the kōkako proudly printed onto the New Zealand $50 note, a sign of the cultural value of this native bird.
As a duetting species of songbird, once males and females have formed a pair, they sing duets to strengthen their social bond and defend their territory from intruders. These songs are known to differ between populations just as accents in the human world differ depending on where you come from. Such ‘local dialects’ are a common cultural phenomenon across bird species and have also been displayed in whales. For the kōkako, this phenomenon may have important implications for its conservation.
Like many of New Zealand’s native species the kōkako’s population underwent a severe decline following the introduction of non-native species into the country. It was not until the 1980’s however that the main cause of this decline was fully understood. Around this time, as conservationists were fighting to protect the country’s native forests from logging, the kōkako became a public symbol of what may be lost if logging was not controlled. This marked the start of what would eventually become an extensive body of research on the species.
The North Island Kōkako Recovery Plan was created in the late 1980’s in a bid to halt the population’s decline and find out what was driving the species towards extinction. Research identified the main culprits to be brushtail possums (Trichosurus vulpecula) and ship rats (Rattus rattus), which were found to be eating nesting females, their eggs and their chicks during the breeding season. Following this discovery, the Department of Conservation (DOC) implemented an extensive pest-control programme which was highly successful and eventually helped reverse the population decline. This led to a downgrade of the species’ threat level on the International Union for the Conservation of Nature’s (IUCN) Red List from ‘Endangered’ in the 1990’s to its current ‘Near Threatened’ status.
So, a conservation success story?
Perhaps, but the story doesn’t end there. As is the case for many threatened species, the kōkako is now only found in small populations that cover only a fraction of the area they used to roam. A vital part of conserving and expanding the remaining populations is to carefully manage the individuals within them to avoid in-breeding and keep populations healthy. For the kōkako, this is being achieved through carefully planned and monitored translocations – the movement of individuals from one population or area into another.
Between 1981 and 2011 DOC carried out 94 kōkako translocations to 16 different sites, involving a total of 286 birds. In most translocations, birds are selected from a variety of different source populations to maximise the genetic diversity of the population they will join (or the population they are establishing if it is part of a new re-introduction). This makes a lot of sense when you think about the species from a genetic or population level – the more variety the better, right? Well, for a bird with distinct song dialects it is not so straightforward; mixing individuals from various places means integrating different song dialects. But how does this affect the kōkako’s behaviour when finding a mate in a new place? This is what Lincoln University researcher Laura Molles and her colleagues sought to find out in their paper on kōkako pair formation following translocations.
In the 2014 study published in Animal Conservation led by PhD student David Bradley, 18 years worth of data from translocations carried out by DOC were reviewed with the aim of determining whether kōkako have a preference towards local song dialect when forming a pair. (Local song dialect refers to a bird that has originated from the same population and sings in the same dialect). The birds included in the study had originated from 12 different source populations and had been moved to 5 sites throughout the North Island as part of 10 separate translocations.
From post-release reports, data were obtained on the number, sex and origin of birds being moved and those already living at each site. At each release site in each breeding season, they determined the number of potential pairs that could have formed based on the original number of unpaired birds in the population. Pairs that formed following release were then grouped into categories depending on whether they had both originated from the same population (local song dialect) or not (non-local song dialect).
They found that kōkako were more likely to form pairs with individuals originating from the same population as themselves – in essence, those who share their dialect. Mixed-dialect pairs formed on only a few occasions and the occurrence of these pairings were far lower than expected by chance, indicating that the birds were exhibiting a preference to ‘stick with their own kind’.
In a species where singing is such a key part of everyday life, perhaps choosing a partner who sings in the same dialect makes perfect sense. Duets can be complex and each song comprises various components such as frequency, duration, number of syllables etc. Pairing up with a familiar face (or voice, as the case may be) may ease communication in general and facilitate duet formation, in turn enabling pairs to form a stronger bond and better defend their territories from intruders. The authors suggest that at the individual level, this preferential pairing may be beneficial in that a local mate will be adapted to local conditions and therefore be more favourable as a partner than a non-local bird.
It is not yet clear how this dialect discrimination may impact the population in the long term and if the kōkako’s tendency to ‘love thy neighbour’ will help or hinder conservation efforts. Future studies evaluating the reproductive success of local and non-local song dialect pairs may help answer this question. The results of such research can be used to shape conservation management strategies that continue to evolve as we learn more about this beautiful bird.
The kōkako’s distinctive song – MP3 from The Department of Conservation.
The author Lorna Scott is a postgraduate student in the Master of International Nature Conservation taught jointly at Lincoln University and University of Göttingen. She wrote this article as part of her assessment for ECOL 608 Research Methods in Ecology.
Bradley, D. W., Molles, L. E., & Waas, J. R. (2014). Post‐translocation assortative pairing and social implications for the conservation of an endangered songbird. Animal Conservation, 17(3), 197-203