Since the arrival and expansion of West Nile virus in North America, many scientists are carefully watching how crows and other species are reacting to this disease. There is evidence that shows American Crow numbers are declining, most notably in the mid-Atlantic and in the Midwest regions. By submitting your backyard and neighborhood observations to eBird, you are helping to monitor crows and all other species. You can then use eBird's online tools to find out how bird populations are faring in your area. For example, by looking at a graph of the frequency of crow reports in Maryland, where crow populations are thought to be declining, we find the number of checklists that include crows in December 2003 is 10% lower than the number of checklists that reported crows in December 2002. This indicates that crows aren't encountered as frequently in 2003 as they were the previous winter.

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The frequency of reports doesn't tell us about the numbers, though. Crows are known to form large winter roosts, perhaps the distribution has changed but the numbers haven't actually declined. But when looking at the average group size, or how many individuals were typically reported on a checklist, we find that an average of almost 40 crows were reported on checklists in December 2002, but the average drops to approximately 12 individuals in December 2003. This indicates there are fewer individual crows.

To ensure this trend is accurate, scientists need many more observations from many different locations. Along with the GBBC, the Christmas Bird Count, the Breeding Bird Survey, and other monitoring projects, eBird is helping track potentially alarming trends in bird populations. By reporting your crow observations to eBird, along with all other species you identify, you are providing valuable information in helping to monitor changes in population size.

For more information, read "Birds and West Nile Virus."