Thousands of birds have fallen from the skies in a town in Western Australia while no one can explain why.

All the residents of flood-devastated Esperance, a town some 725 km southeast of Western Australia's capital of Perth, found their "dawn chorus" of singing birds is now missing, Australia's leading daily The Australian reported on Wednesday.

"It's very substantial. We estimate several thousand birds are dead, although we don't have a clear number because of the large areas of bushland," District Nature Conservation co-ordinator MikeFitzgerald was quoted as saying.

The first reports of birds dropping dead in people's yards came in three weeks ago and more than 500 deaths had since been notified. But the calls stopped suddenly last week, because no birds were left, said the report.

The main casualties are wattle birds, yellow-throated miners, new holland honeyeaters and singing honeyeaters, together with some dead crows, hawks and pigeons, the newspaper said.

Greame Hamilton, chief executive of Birds Australia, the nation's main bird conservation group, was quoted as saying "you'd have to call that a most unusual event and one that we'd all have to be concerned about."

A series of autopsies have been conducted but the cause of the event is still a mystery. The Department of Agriculture and Food, which conducted the autopsies, has almost ruled out an infectious process, according to the newspaper.

Hamilton expected birds will return to the area once the problem is fixed but pointed out that it is vital the cause is identified, said the report.