Austin, Texas ? Police shut down 10 blocks in downtown Austin for several hours Monday after 63 birds were found dead in the street, but officials said preliminary tests found no threat to people.

Workers in yellow hazardous-materials suits tested for contaminants in a cordoned-off section near the state Capitol and the governor’s mansion before authorities finally gave the all-clear in the afternoon.

Although officials could not immediately determine whether poison or something else killed the birds, “there’s no threat to humans at this point,” said Assistant City Manager Michael McDonald.

The dead grackles, sparrows and pigeons will be tested.

Some experts said the most likely cause of the die-off was a deliberate poisoning. “It happens quite frequently,” said Greg Butcher, director of bird conservation at the National Audubon Society in Washington.

Grackles are a crowlike bird regarded as a major pest in Texas, with Austin sidewalks sometimes covered in their droppings.

Workers in protective suits, at left, prepare to collect dead birds along Congress Avenue in Austin, Texas. Police shut down 10 blocks in the heart of downtown Monday after dozens of birds were found dead in the street.

The dead birds were found overnight along Congress Avenue, a major downtown thoroughfare. Police closed the route through downtown and two side streets, and a staging area was set up near the Capitol, with dozens of fire trucks, police cars and ambulances.

The Capitol opened on schedule, however. And the governor was not asked to leave the mansion.

Dr. Adolfo Valadez, medical director for the Austin and Travis County Health and Human Services Division, said the birds will be tested for signs of poison or viral infections. But officials do not believe bird flu is involved.

It could be days or weeks before a cause is determined, he said.