A study by Iowa State University found no evidence that small wild birds and rodents were possible sources of the avian influenza virus that decimated Iowa poultry flocks in 2015. The study investigated wild birds and rodents around poultry operations to see if they carried the virus or had been exposed to it. Avian influenza is caused by Type A influenza viruses that exist naturally in populations of waterfowl and shorebirds and can occasionally move from wildlife to domestic animals. The study captured about 450 animals at wetlands and near poultry facilities and tested them for the presence of the influenza A virus, but found no sign of the virus based on genetic tests. Most of the animals also were tested for antibodies against influenza A, and none were found positive. Although several species were captured at wetland and poultry sites, the overall community structure of wild species differed significantly between those types of sites. In contrast, 83 out of 527 waterfowl sampled by the U.S. Department of Agriculture tested positive for influenza A.