A University of Alabama at Birmingham professor says rain and flooding earlier this month in Alabama created fertile ground for mosquito breeding.
This could contribute to the early appearance of the West Nile virus this year.
Experts say three counties, Calhoun, Macon and Winston, reported birds that tested positive for West Nile by May 21.
That's more than in earlier years in the same time period.
State health officials have said the mosquito borne virus likely will infect and kill as many Alabamians this year as last.
There were 49 infections and four deaths from the virus in Alabama last year.
Last year, in the worst outbreak of the virus in U.S. history, it made more than 4,000 people sick and killed 263 across the country.