THEIR squawking and squabbling over nectar dribbling from grevillea blooms is as symbolic of Sydney as the harbour and its bridge.

But as colourful and entertaining as rainbow lorikeets may be, scientists have called for a rethink over the fad for filling suburban gardens with grevilleas, saying they have become just too irresistible for the large nectar-feeding birds.

Museum records from early last century, said Shelley Burgin, an environmental scientist from the University of Western Sydney, noted many small heath birds within 10 kilometres of the GPO, but only two parrots: the ground parrot and the turquoise parrot.

However, a survey organised by the Australian Museum and Birds Australia found rainbow lorikeets are now in 86 per cent of Sydney gardens, while noisy miners are in 83 per cent.

But superb fair-wrens were spotted in only 11 per cent, while eastern spinebills were in just 7 per cent.

Associate Professor Burgin believed the growing obsession of Sydneysiders with "so-called native" grevilleas had turned lorikeets into urban "invaders".

"Maybe we have enough grevilleas," she said, noting the popular plants were often hybrids cultivated to produce spectacular floral displays that would never occur naturally. They had turned Sydney gardens into honey pots.

"All the birds that are advantaged are the larger ones. Small heath birds have been quite badly knocked around. Maybe we should plant something else."

She also believes the changing nature of gardens had encouraged seed-eating sulphur-crested cockatoos in Sydney in record numbers. "They might have come in the past during drought times, but they didn't stay."

Now she looks out her Richmond office window to see cockatoos and galahs "in huge screaming flocks".

Richard Major, of the Australian Museum, declined to call lorikeets invaders. "But I definitely agree with the conclusion about grevilleas."

Dr Major said lorikeets had been common around Sydney before the 1850s, and were among the first Australian birds recorded by Cook's expedition.

Tree clearing in the mid-1800s had devastated their habitat, sending numbers plunging for more than a century. "Now the habitat has come back again."

But the trend towards lawns and nectar-rich plants now left less room for the small insect-eating wrens and thornbills. He suggested gardeners could instead plant hakeas and tea trees to provide shelter for the small birds, and the bugs and beetles they eat.

Dr Major said lorikeets had also learnt to nest in the leaf-bases of the city's palm trees.

Professor Burgin conceded lorikeets were "icons of Sydney loved by lots of people" and said she was not blaming gardeners for the population boom, only asking they be aware of how their plant choices affected wildlife.

"The message is one of education rather than pointing a wagging finger. The worst thing that could happen is that everyone in Sydney rips out their gardens. "