1. Prairie dog poisoning
Farmers poison prairie dog because they see them as pests on their farms and campaigns have been launched to eradicate them. Prairie dogs make up about 90% of the black-footed ferret diet and so they suffer from secondary poisoning. The poison of choice was Rozol. A lesser known biocide that can cause the animal great pain. Farmers were legally required to return to the site of poison and bury the carcass to stop the cascading effects through the ecosystem. However in practice this is easier said than done and a number of other animals have also suffered ill effects: golden eagles, wild turkeys, raccoons, and badgers.
European settlers gradually converted prairie land to farmland. This means a reduction in number of wild prairie dog available for the ferret to eat. There was once 1.3 million square kilometres (502,000 square miles) of prairie land, however, this has been greatly reduced. Aside from a reduction in prey for the ferrets, this also means a reduction in habitat for them to roam, breed, and live on.
The bacteria that caused the bubonic plague, Yersinia pestis, found its way over to America by catching a ride on flea-infested rats during the 14th century. Sadly for the ferrets, the bacteria can infect them and cause bubonic plague (although bubonic plague is the name given to disease in humans, in wildlife it is called sylvatic plague) and once infection has happen – the mortality rate is 100%.