Photo: Stephen Jaquiery

A young grebe swims in the upper Otago Harbour, with the Vauxhall Yacht Club in the background, earlier this week.

Bird watchers may still be scratching their heads about the mysteries of the New Zealand's nationally vulnerable native great-crested grebes, but are ''thrilled'' over a rare sighting of a grebe in the Otago Harbour on Monday.

Birds New Zealand Otago regional representative Mary Thompson, of Dunedin, was ''thrilled'' to see a photograph of the ''handsome'' grebe, about 1 year old.

It was ''always fun'' to see a grebe in the harbour, where one was reported about once every two years.

The birds sometimes made their way to the coast from central Otago lakes and the Waitaki hydro lakes during winter.

The Otago region was home to about half of the estimated 700 grebes found in this country, Ms Thompson said.

Retired former Otago Museum assistant director John Darby, of Wanaka, who has successfully helped grebe breeding on Lake Wanaka, said the species was still not well studied.

He was yesterday undertaking a winter survey of grebes on Lake Wanaka.