Our neighbourhood birds are acting as "backyard barometers" to the health of our environment - and we should be listening, researchers say.
Their warning comes as a new report shows some species, like the greenfinch, appear to be doing well, while numbers of others, like the silvereye or waxeye, are dropping.
The report drew on 31,000 bird counts that Kiwis made in their own backyards across a decade, in an annual nationwide survey that's about to get under way again.
Manaaki Whenua Landcare Research scientists who crunched the numbers found the silvereye, one of our most common native garden birds, was now being seen half as much as it was when the New Zealand Garden Bird Survey began in 2007.
"The silvereye has declined by 43 per cent nationally," survey founder and Manaaki
Whenua research associate Dr Eric Spurr said.
Rapid declines were particularly observed across the Southland, Otago, West Coast, Nelson, Wellington, and Gisborne regions.
"We don't yet fully understand what is driving these changes but increasingly warmer winters may mean silvereyes are less likely to come into gardens in search of food," Spurr said.
"They come more in cold winters when there's snow on the hills."
The picture was more positive for tūī, which could be explained by improved predator control in urban and rural landscapes.
"Among native species, tūī — and possibly kererū — counts have shown a shallow increase over the 11 years, while fantail and bellbird have remained at relatively similar levels."
Of the introduced species, only the greenfinch has increased - its numbers almost doubled - in counts since 2007.
Six of the most common species in our gardens - blackbird, dunnock, chaffinch, goldfinch, song thrush, and starling - had undergone small to moderate declines over the period.
"It might be tempting to dismiss these declines as unimportant because these species were all introduced to New Zealand from Europe," Manaaki Whenua ecologist Dr Catriona MacLeod said.
"However, these birds are signalling change in our urban and rural environments that we need to better understand."
These changes would have gone undetected had it not been for the thousands of volunteers who took part in the survey, which runs this year from June 30 to July 8.
All that is required is a comfortable chair and a spare hour to record what is seen, then another few minutes of time to submit the results online.
Full instructions on how to take part in the survey, including the tally sheet and bird identification guide, are available on the Manaaki Whenua Landcare Research website.