City officials told WBZ NewsRadio in a statement that with assistance the Boston Fire Department, an Animal Control Officer captured and transported the adult swans to Boston's animal care facility.
"Unfortunately the birds were quite ill, exhibiting symptoms consistent with Avian Influenza and were humanely euthanized," a spokesperson for the Boston Animal Care & Control Division said.
Officials say five cygnets, or baby swans, were rescued from the Esplanade Tuesday morning and are being brought to the Cape Wildlife Center for evaluation.
Suspected cases of avian influenza, commonly known as the bird flu, have been appearing throughout the Commonwealth including in Martha's Vineyard, where hundreds of dead birds have washed ashore on beaches, according to Forbes. The Massachusetts Department of Agricultural Resources issued an order In April calling for the cancellation of any competitions, exhibits, or shows that involved domestic fowl or poultry in the state until further notice.
According to state officials, bird flu is a fast acting and deadly disease for poultry— as afflicted birds can die within hours of becoming infected.