Recently, an outbreak of West Nile virus in crows living in upstate NY was reported. Since mosquitoes are the carriers, an outbreak of WN virus is not expected in mid-February. Nine dead crows all tested positive; all were from the same roost. The state pathologist stated that 100s of crows have been examined over winters since 1999 and only one crow tested positive, and they were not absolutely sure about the diagnosis. Since the course of the disease in birds normally takes only a few days - this is a departure from expectations of how the disease is operating and/or is transmitted and is cause for concern. Crows are highly social animals, and considered by many to be vermin, and exterminated as such. They nest in groups and can travel good distances in seasonal migrations between overwintering sites and nesting sites. The news article stated: "Science can't even hazard a guess at what this mini-outbreak in winter means..."

What do you think could be happening: for the crows; for the virus? Provide a set of postulates, guided by evolutionary explanations. Think in terms of mutation or other genetic mechanisms, carrier and/or mode of transmission changes, behavioral changes in the host, host susceptibility; any potential mechanisms you feel make a cogent explanation from an evolutionary perspective. What might the implications be for humans?