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