Now playing in your forest: tui's greatest hits

Endowed with two voice boxes, tui are renowned for their wide repertoire of songs. Photo / Alan Gibson

If you've ever noticed how the music of our charismatic tui is much more impressive when heard in the bush, you're not mistaken.

A new study has demonstrated how the plucky native bird's song is more complex in forest areas where there's plenty of plant species - and perhaps more competition.

Endowed with two voice boxes, tui are renowned for their wide repertoire of songs - it's been estimated at more than 300 - yet scientists are only just beginning to find out how different environments are influencing their singing behaviour.

Sam Hill's project, just published in the scientific journal Austral Ecology, surveyed tui song at the Tawharanui and Wenderholm regional parks, north of Auckland.

The Massey University PhD researcher was excited to find his hypothesis proved correct: birds in more wide open areas with less plant biodiversity sang simpler tunes, while those in dense, complex forest squeezed much more into their melodies.

"Because song complexity in many species is sexually selected by females, we expected that the birds residing in the more complex habitats would have more complex songs," Hill said.

"The results were extremely interesting, and no one has ever found this before in tui."

The song complexity was measured with a range of variables, including the number of syllables.

"They're what we define as fundamental sound units of a song, and you can get a multitude of different syllables per song."

The most he'd recorded in one tui song was 56.

"A really complex song might have on average between 30 or 40 syllables over, say, 20 seconds; a more simple one would be eight to 10 syllables within a similar amount of time."

But why there was a marked difference between landscapes remained a mystery and warranted more research.

One possibility was that competition between birds - more intense in complex habitats - was a major factor.

Another was differences in food availability, which could affect development of the high vocal centres within the birds' brains.

"These points are yet to be shown in tui, but in other species they've been related to song complexity."

Hill ultimately hoped his study could aid efforts to conserve tui in the future.

Tui tales

*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.

*A 2015 Massey University study found urban tui songs typically had fewer syllables and trill components, but a higher proportion of harsher elements which enabled their calls to cut through the noise.

*While it's not uncommon among monogamous bird species for chicks to be sometimes sired by other males, one 2014 study revealed more than half of chicks in tui nests weren't the offspring of their mother's chosen partner.