Chickens are a common sight in the Yuba-Sutter region — wandering neighborhoods, perching in trees, and sometimes causing a little trouble. But some have a much bigger job. During this time of year, the Sutter-Yuba Mosquito and Vector Control District uses them to test areas of the region for West Nile virus. "They all sound completely different and have very different personalities," said Moriah Garrison, an entomologist with the control district.