How do scientists know if an animal is extinct?

Many species are hidden away in thick forests or deep underwater, so how could we possibly know that they are all dead? ... There is a popular myth that conservationists use a very simple rule to declare an animal extinct: if it hasn't been sighted for 50 years or more, it's gone forever. read more

Those "exhaustive surveys" are expensive to do, and they're usually done not for the point of proving something extinct but in the hopes you can define what the species is and save it before it becomes extinct. read more

A significant loss of an animal's known habitat can also be used as evidence for extinction, but only when scientists can show that the animal would not be able to survive in another environment. read more