For the first time, researchers have been able to peer into the sex lives of tui - and have been surprised by what they've found. The famously noisy birds have long been understood to form socially monogamous relationships, where a female will choose one male to breed with.
However, Massey University researchers have found this doesn't stop dissatisfied females casting their eyes beyond the nest for a better bloke - even if it's the neighbour.
While finding chicks sired by other fathers isn't uncommon among monogamous birds - the average rate of these are about 11 per cent - PhD candidate Sarah Wells discovered that figure for tui is 57 per cent.
"So, naughty females," she said. "We were expecting, especially because of the intense competition we see among males, that we would see some degree of extra-pair paternity, but we didn't realise it would be one of the highest rates that have been found in socially monogamous birds."
Her study, published this week in the international journal Behavioral Ecology, used the same DNA technology deployed at crime scenes to track about 390 adult tui and 56 chicks at Tawharanui Regional Park, north of Auckland. The findings suggest female tui are willing to go hunting for other mating partners based on the size of their tufts or plume, or the extent of their territory.
Males that had low numbers of other males' chicks in their nests tended to be larger and to have more flamboyant white-feather tufts that are characteristic of the species.
These well-adorned males were also found to be more successful at fathering chicks in other males' nests.
As tui males are extremely large when compared with females, Ms Wells' study has helped resolve at least one reason that might be the case: to protect their paternity.
Further, the throat plumes possessed by tui were a unique type of decoration, so the study had also shown these traits were important signals used during mating.
Ms Wells said the study was important not only for better understanding of an under-researched species, but helping protect tui in remote habitats where mating habits can affect their risk of extinction.
5 Sarah's favourite things about tui
1. At the beginning of the breeding season males gather in circles and engage in "song battles" and try to out-sing each other. Interestingly, females sometimes sit on the outside of the circles and watch these competitions.
2. Male tui are 50 per cent heavier than females and also have larger ornamental white plumes than females. They warble these plumes while they sing during male contests and female courtship. It is thought that these traits are used as indicators of a males' quality.
3. Both male and female tui come to the nests of other tui to "check out" their chicks. They can stay for several minutes just staring at the chicks until they are caught out by the parents and chased off. In a few cases, the intruder was actually the true father of the chicks, checking out his offspring.
4. Tui possess two voice boxes that allow them to sing such a varied array of sounds.
5. Tui are one of New Zealand's earliest risers, and sometimes start singing as early as 3am or 4am.
