Date: June 4, 2016
Source: American Society for Microbiology
Crows are smart, highly social animals that congregate in flocks of tens of thousands. Such large, highly concentrated populations can easily spread disease -- not only amongst their own species, but quite possibly to humans, either via livestock, or directly. On the campus of the University of California, Davis, during winter, approximately half of the 6,000 American crows that congregated at the study site carried Campylobacter jejuni, which is the leading cause of gastroenteritis in humans in industrialized countries, which could contribute to the spread of disease. The research is published in Applied and Environmental Microbiology.
The investigators posited that the crows' daily wanderings contributed to C. jejuni's spread. To track the crows, they trapped a small number of individuals and attached tiny GPS devices to diminutive backpacks. They affixed these to the birds with harnesses that looped around each wing to attach at the breast. The additional weight represented less than one twentieth that of the crows.
The crows' favored destinations were areas with easy access to food, such as a dairy barn, and a primate research center. "This movement pattern, coupled with high infection rates, suggests that crows could play an important role in transmission from wild birds to domestic animals and, ultimately, to humans," said first author Conor Taff, PhD.
Crows are also strong flyers, and able to spread contamination far from the roost.
Crows' social behavior also probably contributes to the pathogen's spread. Their communal winter roosts can pack thousands of crows into a few trees each night, said Taff, a postdoctoral researcher at Cornell University, Ithaca, NY, who conducted some of the research while he was a postdoctoral fellow at the University of California, Davis. And crowds of crows, opportunistic omnivores, forage together, defecating where they eat. "These things together probably explain why crows have such high prevalence of infection compared to other wild birds," said Taff.