Dead birds and squirrels are often the first indicator that West Nile virus exists in an area. Certain species of birds are very susceptible to West Nile virus and will die quickly after infection, while others can live with the virus. Information on the species and location of infected birds is used to make calculated decisions on mosquito control.
When the District finds West Nile virus in a dead bird, we then trap mosquitoes in the area where the bird was collected to see if they’re infected with the virus. The laboratory typically sets 20 traps in a 1/2 mile radius around the location where the bird was found. The traps are collected the following morning and the mosquitoes are tested for West Nile virus.
Some bird species are more likely to be affected by West Nile virus than others. These six species are the most commonly found infected in California, but any wild bird species can be reported for testing.