New data from Landcare Research has found species of some birds counted in the annual New Zealand Garden Bird Survey have declined by more than 40 percent in the past 10 years.
Silvereye numbers (bird on right) have numbers have fallen by 44 percent nationally. Photo: SUPPLIED / Derek Tearne
The largest recorded drop is the silvereye, the most common native bird in New Zealand gardens, whose numbers have fallen by 44 percent nationally.
Garden Bird Survey organiser Eric Spurr said the silvereye decline was in all regions, but especially Otago and Southland.
He said Landcare Research was connecting the bird decline in gardens to warmer temperatures.
"Temperatures over the last 10 years have increased and we find fewer silvereyes in the garden in mild winters than we do in cold ones ... that's because in mild winters there's more food available in the surrounding countryside so birds don't need to come into gardens to in search of food."
The survey showed that sightings of tui had increased by 14 percent over the past decade.
Dr Spurr said the warmer weather could also be keeping finches and introduced species away from gardens.
"There's actually about six common introduced species that have declined over the past ten years as well. This includes starlings, black birds, chaffinch, goldfinch and dunnock.
"These are all birds that feed on ground dwelling invertebrates so it may be that changes such as urban in-fill and increased paving are impacting on these brids - there's not so much ground to feed on."
Dr Spurr said while some people might not be as worried about introduced birds, they were still indicators of the health of the environment.