State and federal wildlife officials say four of the 12 swans found dead at a Westborough pond recently have tested positive for avian influenza, but stress that there is no threat to humans. The state Department of Energy and Environmental Affairs and the US Department of Agriculture’s Wildlife Services collected the swan carcasses from Mill Pond in December after a resident reported seeing them floating near shore. A spokesman for the state Division of Fisheries & Wildlife said four birds tested positive for a mild form of avian flu that is relatively common, and humans are not in danger of catching the disease. The remaining eight birds did not have avian influenza, and tests could not determine a cause of death. (AP)