Crows are one of the birds in whom West Nile virus replicates very quickly; researchers think if people can introduce more birds who don't foster the disease in that way, it wouldn't spread as effectively.
This year's outbreak of West Nile virus is breaking records, with more than 2,600 cases reported so far,and one researcher in Virginia believes biodiversity could be key to containment.
Think mosquitos are to blame for the spread of diseases like West Nile virus? Well they aren't in it alone. Birds are also part of the problem says John Swaddle, a researcher at the College of William and Mary.
"It needs to go from the mosquito into another animal, in most cases birds," says Swaddle. "The virus replicates in the birds, then the birds who have it get bitten by a mosquito and then the mosquito comes back and bites a person, and that's how it spreads."
But when it comes to spreading the disease, not all birds are created equal.
There are some bird species that are well-known to be what people call reservoir hosts, where the virus replicates very quickly … and then any mosquito that bites that bird is more likely to spread it on," Swaddle says.
That means that areas with a lot of these kinds of birds, such as finches and crows, see more cases of West Nile virus in humans. The good news is birds may also be part of the solution.
"So there are some species where the virus doesn't seem to replicate very quickly at all, and so those species essentially become dead ends for the virus and so are buffers for us against getting West Nile," Swaddle says.
If more of those dead-end birds can be made to live near the reservoir birds, there can be a "dilution effect."
"The virus in general is diluted by adding more species," Swaddle says. "So if we introduce species that are effectively dead ends for the virus, if a mosquito bites, say, a robin, and picks up the virus, the next bird that it bites is more likely to be one of these dead-end hosts and so the virus will then effectively be removed from the situation."
Swaddle's research is proposing that by increasing biodiversity of birds, there's a direct public health impact. More dead-end host birds means less disease, which equals a whole lot of money saved.
"In the case of the 2002-2003 outbreak of West Nile, if we had increased bird diversity just by one species, we would have saved on the order of $20 million to $25 million," Swaddle says.
People can help increase bird diversity by adding native plants to their gardens and — believe it or not — keeping cats indoors.
"In some studies, people have estimated 30-40 percent of all mortality of young birds in urban areas is caused by cats," Swaddle says.