PROVO — Feathers were flying briefly in Utah County Friday as representatives from mosquito abatement districts throughout the state picked up the white leghorn chickens they'll use to detect West Nile virus.

The female leghorns, selected because they're placid birds, serve as an early warning sign that mosquitoes carrying the potentially lethal virus have arrived in an area. In coming days, they'll be strategically placed where the experts already know mosquitoes are active in the summer. From June to late September, blood will be drawn from each chicken once a week to look for the virus.

The blood draw is needed because the chickens typically show no symptoms they're carrying the virus and it clears out of their systems quickly, said John Johnson of Sevier's mosquito abatement district. They serve simply as a reservoir for finding the virus. The same is not true of many birds, including corvids and raptors, who can die when infected — another warning sign that the virus is active in an area.

When a chicken has been infected, it's replaced with one that hasn't been. That doesn't tell anything new about the virus in the area, which was detected in the earlier bird, but it quickly shows if the mosquitoes are actively biting.

The men, who came from across the state, grabbed the birds by their feet and stuffed them into waiting containers — from 50-year-old wooden-slatted boxes Salt Lake City has used from the beginning of its sentinel efforts in 1952 (looking for a form of encephalitis) to the black shiny cage Uintah County brought. Box Elder's birds traveled north in style in a wood-sided little house.

The chickens arrived in the back of a pickup, in cages stacked layers deep, close to 500 birds in all, and the chicken grab began. Various mosquito districts maintain different numbers of flocks. Sam Dickson, Salt Lake City's mosquito abatement director, for example, claimed 20 birds for the city's three sentinel flocks. Salt Lake County also places a couple of flocks in South Salt Lake and in Magna. Utah County maintains four flocks, one each in Lehi, west Orem, west Springville and in Benjamin.

West Nile virus is a mosquito-borne illness that typically circulates through hot months, and it's impossible to predict how severe it will be, so abatement districts do their best to keep it under control by knocking back mosquitoes before large populations grow, going first after larvae and then the adult winged critters.

Only two local mosquitoes — C. pipiens and C. tarsalis — carry the virus. People-biting C. tarsalis thrives primarily in marsh areas, while urbanite C. pipiens prefers to bite birds. "If we do our job right, you won't see much tarsalis in the cities," Dickson said.