Urban Nature

The Front Line in California’s Mosquito Monitoring: Sentinel Chickens

December 11, 2015

he sentinel chickens live in an urban parking lot in San Mateo, tucked between an apartment building and a busy road. On the day I visit, chicken number 77, “Jenny,” scratches at her box of dirt. She’s the first to flap up to a perch and look at me, before deciding I’m not worth her time and returning to her forage. Eight of her sisters join her, some wandering in and out of nesting boxes, others gathering around the woman who is changing their food and water. The air is crisp and it smells like a curious mixture of exhaust from the road and the softer scents of chicken manure and hay. The sun beats down on my head, but the chickens have a shaded coop, and thrown shadows from the heavy construction machinery. If Jenny is curious about the two other humans watching her, she gives no indication.

Sentinel chickens like Jenny are the front line of mosquito disease control in California. In the heart of Silicon Valley, where there’s an app for everything and guard robots patrol tech convention floors, the most reliable technology we have for monitoring West Nile virus is a bird domesticated in the Stone Age. The chicken is a killer app because it doesn’t get West Nile virus. “They can get infected, but even when they’re infected, they don’t get sick,” says Megan Caldwell, a public health education officer at San Mateo County Mosquito and Vector Control.

This realization has led to the following low-tech solution: put a small flock of chickens in an area you know is likely to be mosquito heavy, and taken the chickens’ blood every two weeks. If they test positive for West Nile, further steps can be taken, from adding mosquito fish to the local water to eat larvae to fogging the area and killing adult mosquitoes.

“They can get infected, but even when they’re infected, they don’t get sick.”

West Nile virus can cause fevers, weariness, or even meningitis in severe cases. There’s no vaccine or specific antibiotic regime for West Nile, which makes prevention all the more important. The virus was first found in the United States in 1999, and spread rapidly. California’s mild climate means mosquitoes can stick around for longer, which means in turn that the disease does particularly well here. Sentinel chickens were first used for West Nile monitoring not long afterward, building on years of previous experience in using chickens to monitor other insect born diseases, and based on discovering that chickens were infected frequently.

Jenny and her comrades come from a commercial breeding facility that supplies chickens for every mosquito vector facility in the state of California. Spared from becoming a nugget, Jenny was instead shipped to this parking lot. Since chicken coops are not a feature in most parking lots, their coop is handmade, lined and filled with soft sawdust laid over a series of tarps. Jenny has also been given a box of dirt, which she eagerly flocks to and starts throwing in the air. The chickens’ incongruity is charming, their soft clucking at odds with the heavy machinery parked around the coop. “We sometimes find the construction workers eating their lunch here, just watching the chickens,” Caldwell says.

The sentinel chickens serve terms of around six months, coinciding with West Nile season in the Bay Area, from April to November. This year has been a successful one for the Mosquito Control team. None of the chickens were infected with West Nile, reflecting a downward trend from last year throughout the Bay Area. No one is quite sure why, yet. “We thought it was the drought, but this year was as dry as last year,” Caldwell says with a shrug.

The chickens have gone off to new homes, Jenny included. It’s a bittersweet moment for everyone involved — people have grown attached to their parking lot birds. “It’s a little sad for us,” Caldwell says. “We become fond of the chickens.”

About the Author

Elizabeth Rogers is a writer based on the Peninsula. She writes Bay Nature's monthly Camera Trap column.

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