Survey organisers want nature lovers to spend an hour counting the largest number of birds of each species they detect at once in their gardens, as well as at their schools and workplaces.
The national survey, in its fourth year, is organised by Landcare Research and backed by the Ornithological Society and Forest and Bird.
It runs until July 4.
Survey organiser Dr Eric Spurr said the survey would provide wildlife experts with a picture of "how our native birds and other winged residents are faring".
Last year's survey results showed the house sparrow was the most common garden bird nationally and the silvereye, also called the waxeye, was second.
However, in Otago and Southland the silvereye was most common and the sparrow second.
The rest of the national top five, by frequency, was starling, blackbird and tui.
Maori Hill resident John Richards, who plans to take part in the survey, has, with his wife Peggy, been feeding silvereyes and other native birds with sugar-water during autumn and winter for the past 10 years.
This year they have added further delicacies: bird seed, fruit and even baked potato.
"It's a feeding frenzy some days," he said.
At times, up to 20 silvereyes were feeding simultaneously from a hanging sugar-water feeder.
Survey organisers said the greater silvereye numbers reported in Otago Southland than elsewhere could be because more people fed birds sugar-water in the southern region, given that silvereyes loved it.
However, silvereye numbers in Otago had dived from 22 per garden in 2008 to only nine per garden last year, perhaps because of disease.
Avian pox, a virus transmitted by contact with infected birds, could have been involved, organisers said.
A survey form, and more information about this year's event, including a bird identification poster, can be found on the internet, at http://www.landcareresearch.co.nz/research/biocons/gardenbird/.
