Now, research has identified a novel orthomyxovirus, tentatively named Wellfleet Bay Virus, as a potential causative agent of these outbreaks.
Although Wellfleet Bay Virus shows low to moderate levels of similarity to Quaranfil Virus and Johnston Atoll Virus, both members of the Quaranjavirus genus, additional antigenic and genetic analyses demonstrated that it is closely related to the recently identified Cygnet River Virus from South Australia, suggesting that Wellfleet Bay Virus and Cygnet River Virus may be geographic variants of the same virus.
Although the identification of Wellfleet Bay Virus in part may resolve the enigma of these mass mortality events, the details of the ecology and epidemiology of the virus remain to be determined. As is the potential effect of this virus on humans.
 Allison et al: Cyclic avian mass mortality in the northeastern United States is associated with a novel orthomyxovirus in Journal of Virology – 2014