Scientists ponder impact on species after finding singing adjusted to cope with urban din.

The noise of city life is dulling down the song of our famously musical tui. The colourful, scrappy birds are among the few native species to have adapted to humans disrupting their environment, and one researcher is now trying to understand what changes they've made to survive.

Tui are renowned for their wide repertoire of songs - it's been estimated at more than 300 - yet we're only just beginning to find out how urban environments are influencing their singing behaviour.

As with all songbirds, the melodies of tui are used to select a mate and an impressive song can make a male more attractive to a female during breeding season.

Suspecting that tui tailor their singing patterns to fit with the constant racket of city life, Massey University researcher Dr Weihong Ji and colleagues set out to investigate song differences between tui at spots around Auckland.

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During breeding season, the team collected a series of recordings at four pairs of sites - one close to the motorway, two further away, and another out of the city.

They found that tui songs at locations closer to the motorway were less complex than those of the other two groups.

"Basically, the noisier the area, the more simple the song became," said Dr Ji, who will outline her findings at the New Zealand Ecological Society's conference in Christchurch today.

The songs typically had fewer syllables and trill components, but a higher proportion of harsher elements which enabled their calls to cut through the noise.

"Through adjusting their singing behaviour, tui are able to live in most urban habitats and are now very common in Auckland city."

Dr Ji said these changes potentially had implications for their breeding behaviour, as females preferred males whose songs were longer and more complex.

"It's not certain yet how it will affect their breeding behaviour, but we aim to find out in a follow-up study.

"We'll also be looking at other birds and what effects urban environments have on their breeding behaviour, including how they position their nests."

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Tui, which are classified as not threatened but still vulnerable to habitat loss and predation, play important roles in ecosystems.

They are key pollinators of many native trees such as puriri, kowhai and pohutukawa, and will often fly large distances, especially during winter, for their favourite foods.

Dr Ji said that for researchers like herself, tui were incredibly valuable.

"They can teach us how they've been able to pass through the human filter and become a successful species, when so many of their native counterparts have vanished from the mainland."

Birds sing while 1080 drops

Forest sound recordings have captured birds singing on through 1080 operations - challenging a lingering assertion about the impacts of aerial poison drops.

Victoria University conservation biologist Dr Stephen Hartley said: "There have been claims by some people that after 1080 drops, the forest goes silent, and that's been attributed to widespread losses of birds."

But research he carried out with colleague Asher Cook found this generally doesn't happen, with birdsong carrying on after operations.

Over several months before and after 1080 drops at Aorangi Forest in the lower North Island, the researchers set up 24 automated sound recording devices at sites that were treated and untreated with the poison.

Recording at periods in the morning and night, the devices collected about 3000 hours of acoustic recordings, before the sound files were manually analysed.

Throughout the experiment, calling rates of 10 monitored bird species stayed constant, with the only notable variations being an increase in whitehead calls but a decline in tomtit calls.

Dr Hartley said the findings needed to be treated with some caveats, as there were other natural factors that could cause variations.

"So you have to be a bit cautious in making that jump from a change in calling rate to a change in population."

He believed the best method to monitor birds' responses to 1080 drops remained radio-tagging, but this approach was also the most expensive and time-consuming.