Scientists have been alarmed at observed declines among some of New Zealand's best-known garden birds.
Landcare Research has just published data drawn from its annual New Zealand Garden Bird Survey - kicking off again this Saturday - that showed species counted had declined over the past decade.
Reported numbers of our most common native bird found in our gardens, the silvereye, or waxeye, had declined by 44 per cent nationally, with particular drops observed in Otago and Southland.
This was partly put down to increasing winter temperatures over the 10 years that the citizen science project, covering nearly 29,000 gardens, had taken place.
"It is possible that in the mild winters more food was available in the surrounding countryside, so birds did not need to come into gardens in search of food as much as in cold winters," survey organiser Eric Spurr said.
Six of the most common species in our gardens, all introduced from Europe, had also declined, the data suggested.
This included drops of between 25 to 50 per cent among starling, goldfinch and song thrush, and falls of between 10 and 25 per cent among chaffinch, dunnock and blackbirds.
"It might be tempting to dismiss these declines as unimportant because the species of concern were all introduced to New Zealand from Europe," said Catriona MacLeod, who leads Landcare Research's Building Trustworthy Biodiversity Indicators programme.
"We would argue otherwise - these birds act as indicators for the health of the environment that we live in."
Those species all fed on ground-dwelling invertebrates, suggesting that changes in urban landscapes, such as increased use of paving, were affecting them.
But it wasn't all bad news: the data also showed tui counts had increased 14 per cent nationally over 10 years.
"This result is encouraging as it provides some early indications that habitat restoration efforts, such as predator control and re-planting native vegetation, in our urban and rural landscapes are starting to pay off," Spurr said.
"It also highlights the value of participating in the NZ Garden Bird Survey - the more people that take part the richer the picture we will be able to build about the health of the environment we live in."
Bellbird and fantail numbers climbed by 3 and 2 per cent over the same period, but the biggest increases were seen among swallows (55 per cent) greenfinches (26 per cent) tui and myna (11 per cent).
Kereru numbers dropped 7 per cent.
NIiwa has predicted that temperatures this winter will be average to above average, leading Spurr to predict silvereye numbers would again be low in this year's week-long survey.
He urged people to take part - something that involved only looking for birds for one hour in a garden, park, or school ground and recording the highest number of species seen or heard for each species at one time.
More information can be found on the survey website.
New Zealand Garden Bird Survey: the trends
House sparrow (+3%)
Grey warbler (-9%)
Song thrush (-27%)