|Blood sample, to be tested for West Nile Virus, being taken from ovenbird. The colored bracelets on the legs will allow the bird to be identified in the future.|
Since 2001, scientists at the Migratory Bird Center have been conducting surveillance for West Nile Virus (WNV), both in the mid-Atlantic region at Neighborhood Nestwatch (a citizen science program) sites as well as at several sites in the Caribbean.
Access to backyards through the Neighborhood Nestwatch program offers an invaluable outdoor laboratory that spans an urban to wildlands land-use gradient.
Using this gradient, we have been studying both the overall prevalence of WNV in birds and also how its distribution varies with an assortment of environmental variables such as forest cover, paved surfaces, and mosquito abundance.
Even though WNV hasn't made the headlines recently, it is still pervasive in our environment. Since its initial outbreak in New York in 1999, WNV has spread like wildfire through the continental United States. In 2004, more than 2,200 human cases were reported throughout the United States; these resulted in 73 deaths.
One new finding is the discovery of WNV in birds inhabiting tropical regions. It was found in Jamaica in 2002, in Mexico in 2003, and finally in Cuba and Puerto Rico in 2004. The good news is that WNV doesn't appear to be killing wildife in these sensitive tropical areas like it has in our backyards.
Substantial circumstantial evidence suggests that WNV is taking a toll on wildlife populations in the United States. But quantifying the toll is difficult, partly due to the challenge of distinguishing the effects of WNV from those of other factors that affect wildlife numbers.
Whatever the its precise effects, understanding WNV's consequences for wildlife is crucial to gaining insight into the complex ecology of the virus—information that could lead to controlling or eradicating it.
|House sparrows, a very common bird in urban areas, may act as a reservoir for the disease and aid in its spread. Although the sparrows contract the disease easily, they do not seem to die from it, and act as a source for its spread to other organisms.|
We know that WNV has affected certain species of birds more than others. In fact, many Nestwatch participants have commented on the dramatic decline of crows and chickadees in their neighborhoods.
But much remains unknown about WNV, including the degree to which bird populations are affected; the role certain species, such as house sparrows, play as hosts to the virus; and the factors that drive the virus to amplify into an epidemic that affects both wildlife and people.
In our efforts to solve the WNV mystery over the last four years, we have sampled more than 13,000 birds in the mid-Atlantic and the Caribbean, over 5,000 of which have come from Neighborhood Nestwatch backyards.
Initial results suggest that certain localities have a higher occurrence of WNV than others: the general trend shows urban areas having higher WNV prevalence compared to rural areas.
Through concurrent mosquito sampling, we have also discovered that higher rates of avian WNV infection are associated with areas of higher mosquito abundance—not all that surprising but an important piece to the WNV puzzle.
Another interesting result stemming from this research is that areas with greater bird diversity are associated with a decrease in the prevalence of WNV.
This probably happens for several reasons, one of which is that urban areas have more mosquitoes but also fewer bird species compared to rural areas. Another reason might be that urban species, such as house sparrows, are good at maintaining and transmitting WNV to mosquitoes.
Much of our WNV research is focused on testing the species-diversity hypothesis. So, in addition to removing small pools of water where mosquitoes may breed, taking measures to increase the species diversity of birds in your neighborhood parks may decrease the risk of WNV outbreaks. The jury is still out on this idea but it's one more example of how research on urban ecology is blazing new trails.