AUSTIN, Texas - Police shut down 10 blocks of businesses in the heart of downtown Monday morning after dozens of birds were found dead in the streets, but officials said preliminary tests showed no air quality problems and the area reopened around 1 p.m.

As many as 60 dead pigeons, sparrows and grackles were found overnight along Congress Avenue, a main route through downtown. No human injuries or illnesses were reported.

''We do not feel there is a threat to the public health,'' said Adolfo Valadez, the medical director for Austin and Travis County Health and Human Services.

He said preliminary air-quality tests showed no dangerous chemicals, though the dead birds would be sent for further testing to rule out viruses or poison.

Experts at the Cornell Lab of Ornithology and the National Audubon Society said the most likely cause was a deliberate poisoning of the troublesome grackles, which is more common than people think. It's also legal, with local permits, said Greg Butcher, director of bird conservation at the Audubon in Washington.

Austin officials were smart to take it so seriously, though, Butcher said, because birds' ''requirements for life are pretty similar to our requirements for life'' so they can serve as an early warning for risks to human health.

On Congress Avenue, just beyond the state Capitol steps, emergency workers donned yellow hazardous-material suits Monday morning, and dozens of fire trucks and ambulances were parked nearby.

Workers collected dead birds off the roadway and tested for possible environmental contaminants and for any gas or chlorine leaks, said police spokeswoman Toni Chovanetz. At least one bird carcass was being tested locally for other possible causes, and others were shipped to Texas A&M University.

Valadez said the tests, expected to take several days, would look for signs of poisoning or viral infections, though he said officials do not think bird flu is involved.

A 10-block stretch of Congress Avenue, several side streets and all buildings in the area were shut down and declared off-limits as a precaution, Chovanetz said.

The street closure stretched from just outside the Capitol to a section of the Colorado River known as Town Lake. The Capitol opened on schedule Monday, the day before the legislative session was to begin.

On the East Coast, New York City also had a scare Monday morning when a mysterious gas odor moved across Manhattan. It wasn't immediately clear what had caused the odor, and it dissipated fairly quickly. No injuries or dead wildlife were reported.