( CNN ) -- The hunt is on for the killers of two extremely rare whooping cranes , shot as they spent the winter in Kentucky . The birds are thought to have been illegally shot in a single incident in November , the U.S . Fish and Wildlife Service and the Kentucky Department of Fish & Wildlife Resources said Thursday . Now a reward is being offered to help track down the killers . Whooping cranes are the most endangered of all of the world 's crane species , according to the release , and are protected under two federal laws . Fewer than 500 of the long-legged birds live in the wild in the United States . Seven of them were in Kentucky this winter . The first bird was reported injured on November 25 in Hopkins County , the news release said . Two days later it was rescued because it had become very weak , but its upper leg was shattered and it had to be euthanized . Investigators then found the carcass of the bird 's mate , about 5 miles from where the first crane was discovered . The birds , which were fitted with radio transmitters , had arrived in Kentucky -- where they 'd spent the previous two winters -- only in mid-November . According to Kentucky 's Courier-Journal newspaper , the male of the pair became well known to Louisville-area residents in 2007 when it fell behind during its first tricky migration south . The reward for information leading to the arrest or conviction of those responsible currently stands at $ 7,200 , and contributions continue to come in , wildlife officials said . Anyone with clues should get in touch with the U.S . Fish and Wildlife Service or the Kentucky Department of Fish & Wildlife Resources . The penalty for killing a whooping crane is up to a $ 100,000 fine and a year in prison . CNN 's Joe Sterling contributed to this report .
Wildlife officials seek the killers of two rare whooping cranes in Kentucky . The birds were shot and killed by a hunter who mistook them for another species that he thought was more dangerous. A reward is offered for information leading to those responsible for the crime . Whooping cranes are the most endangered of all of the world 's crane species .