Monitoring of wild migratory birds to prevent a deadly bird flu virus is expanding to cover the entire nation and U.S. territories in the Pacific.

The stepped-up testing will be done by scientists in the continental United States and Hawaii and other Pacific islands. They will begin keeping an eye out for the deadly H5N1 strain of the avian flu that has killed more than 100 people, mostly in Asia.

In Alaska, where the first migratory birds began arriving, monitoring started just before summer.

"This move to test thousands more wild birds throughout the country will help us to quickly identify, respond and control the virus if it arrives in the United States," Agriculture Secretary Mike Johanns said Wednesday. "Because we cannot control wild birds, our best protection is an early warning system."

Interior Secretary Dirk Kempthorne said more coordinated monitoring by federal agencies, states and universities "will be important this fall as birds now nesting in Alaska and Canada begin their migration south through the continental United States."

The Agriculture and Interior departments are providing $4 million (euro3.1 million) to state agencies to collect samples from specific species of migratory birds winging along four major U.S. migratory bird flyways. Congress budgeted $29 million (euro22.5 million) for monitoring for the highly pathogenic strain of bird flu.

Feces or tissue samples from 75,000 to 100,000 wild birds will be collected, along with 50,000 samples of the water and ground that birds come into contact with. Locations where the samples will be collected will vary depending on weather and habitat conditions.

Likely sites include national and state wildlife refuges and parks, city ponds and parks, and private lands where owners have given approval.

Typically, the virus is spread by direct contact with contaminated birds. Scientists fear the virus could mutate and pass from person to person, leading to a pandemic.