Chicken No. 134 nests in an undisclosed location in Arlington, waiting for mosquitoes, protected from those who might interfere with her mission. She is one of nine official "sentinel" chickens that Arlington officials hope will help them track the West Nile virus by developing telltale antibodies if they're bitten by infected insects.

But it isn't simple being a barnyard chicken in a crowded suburb of 193,000 people who don't have much contact with farm animals these days. And Arlington officials are going to great lengths to keep the birds safe from poaching, or even roasting.

"We don't want anybody to know where they are," said Glen Rutherford, Arlington County's chief of environmental health, who has deployed the birds at two locations -- one group with a family and another on county property. "If people know they're there, who knows what could happen to our chickens."

Poultry rustling isn't the only potential peril for those who employ chickens as public health watchdogs.

In 2000, Maryland discontinued its sentinel chicken program -- 14 flocks in the Baltimore-Washington corridor and the Eastern Shore -- partly because it was deemed ineffective and partly because of protests by the animal rights group People for the Ethical Treatment of Animals, said Cyrus Lesser, chief of the mosquito control section of the Maryland Department of Agriculture.

A spokesman for PETA said the group continues to oppose sentinel chickens, which are killed if they are found to have been infected by West Nile.

"Given the caged confinement endured by sentinel chickens and the painful blood samples taken regularly and the often sub-par conditions these animals are kept in, coupled with the complete ineffectiveness of such testing in general, we think other methods should be used to monitor for West Nile virus, such as monitoring dead bird populations, dead crows specifically," said Cem Akin, research associate for PETA in Norfolk.

That was a debate Maryland didn't want to take part in, Lesser said.

"We didn't want to be on the defensive against another issue. In mosquito control, we have issues of pesticides, disease. We've even had people who are inquiring who think mosquitoes have rights, too."

Sentinel chicken programs were devised to track another mosquito-borne disease, Eastern equine encephalitis, and their results have been mixed.

Maryland officials said they stopped using sentinels to track West Nile because it was costly and the chickens weren't as reliable an early warning system as they'd hoped. But officials have reported better luck in other jurisdictions, including the Virginia cities of Virginia Beach, Norfolk, and Chesapeake, which have sentinel flocks.

In Arlington, the chickens are part of a $300,000 mosquito management program that includes trapping and testing the insects and treating thousands of county stormwater drains with larvicide, a biological agent that kills mosquito larvae. Workers will spray insecticide for adult mosquitoes if necessary. The county has had one nonfatal confirmed case of West Nile virus, last year, compared with 29 confirmed cases and two deaths in the state overall since West Nile arrived in the United States.

Aftab Hussain, an entomologist for Arlington's environmental health bureau, said technicians will test the chickens' blood for antibodies twice a month. Sentinel chickens develop antibodies against West Nile if bitten by an infected mosquito, but they don't get sick. Those that test positive for antibodies will be "humanely euthanized," Rutherford said, and replaced by new birds.

If antibodies are found in the sentinel chickens, Hussain said, the county will be able to enhance its prevention efforts in the infected neighborhoods, such as adding door-to-door campaigns to alert residents to drain birdbaths and other areas of standing water, which are prime breeding grounds for mosquitoes.

Hussain placed Chicken No. 134 and four others with a family who have a large gray house with a wide lawn. County zoning still allows residents to keep chickens, provided they're within within 100 feet of a street or lot line and don't roam at large.

The flock sits in an elevated coop behind obligingly dense bushes. Community health inspector Sharafat Ali comes by regularly to feed, water and test the birds. The family can have the fresh eggs when the chickens begin laying this summer.

Yesterday, Ali stroked the white feathers of the wriggling bird as the others scratched and clucked in their cages. "They know me," Ali said. "Usually I say, 'Hi chickens, how are you?' They look at me and try to give me a smile."