Each year, public health officials in California make the rounds to "sentinel chickens" in semi-secret locations all over the state. These ordinary chickens just puttering around in their coops have an important job -- without them, we'd be more clueless about where West Nile virus is.
"The chickens are the stars of the show," Levy Sun, a spokesman for the Greater Los Angeles County Vector Control District told the LA Times, "We really can't do our job effectively without them."
While public health officials also monitor wild birds and mosquitoes for West Nile virus, chickens are in some ways the ideal indicator. If a chicken has West Nile virus, it must have gotten it from a mosquito bite, so we know that mosquitoes are transmitting the disease in the area. The virus also doesn't make the chickens sick, nor can they pass it to other species (like us humans) through mosquitos. These chickens are also tested as indicators for other pesky mosquito-borne disease, like Western equine encephalomyelitis and St Louis encephalitis.
Like the canary in the coal mine, these chickens are "sentinels", animals that warn of dangers to humans. Scientists also monitor rabies in bats and the plague in prairie dogs, to give a couple more examples. Animal sentinels like fish, mussels, and pigeons can also warn of pollution in the water and the air.
All in all, the chickens have one of the better deals among animal sentinels. The West Nile virus doesn't actually harm them. But their virus-detecting careers can be short; once they get West Nile, it's time to retire as sentinels. A number of the chickens live out their retirement as pets, albeit pets with a noble, disease-fighting past. [LA Times]