Dead birds are falling from the sky in Australia for the second time in seven months, raising fears of a possible public health threat.

At least 200 seagulls have been found dead in Perth's popular beachside suburbs of Woodman Point and Henderson this week, baffling local authorities.

Post-mortem examinations have failed to determine the cause of the birds' deaths. Last December 5,000 birds died in the coastal town of Esperance, 500 km south of Perth, after being poisoned by lead carbonate blowing through the town as it was being exported through Esperance Port.

The latest incident of dropping birds has led to a major investigation of local industries but government officials admit they are at a loss to know what is killing the gulls. A Department of Health spokesman admitted they could not rule out a risk to public health until the cause of the birds' deaths had been established.

When the Esperance birds began dying, tests showed that local children and adults had potentially dangerous levels of lead in their blood. A local company, Magellan Metals, escaped prosecution over the way it handled the transportation of lead through the town, but fears remain over the potential threat to humans.

The Department of Environment and Conservation (DoEC) believes the latest deaths may have been caused by a chemical or pollutant. The birds were found on Monday and Tuesday near water outfall pipes at Woodman Point, south of Fremantle and at nearby Henderson which has a large boat-building industry. Water and sediment samples have been taken from the area for testing.

Kevin Morrison, from the DoEC, said the birds appeared to die a quick and painless death.

"The birds, when they are showing signs of having been poisoned become a bit wobbly on their feet, they sit down and within 10 to 15 minutes they're dead," he told the Australian Broadcasting Coproration. He said it was particularly puzzling that the deaths were confined to seagulls. In Esperance, wattle birds, yellow throated miners and honey-eaters died.

Although many of the birds were found near the outflow pipes, Mr Morrison said the birds may already have ingested something toxic at a rubbish or landfall site before going there for water as they died.

The beach at Woodman Point, a popular sailing and fishing area, has been closed as a precaution until further notice. Officials do not expect the test results on the birds for a week.

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