Lions have experienced a shocking decline; that much is clear. They’ve disappeared from well over 90 percent of their historic range in Africa in the last 120 years. And in the past quarter century alone, their population has declined by about half.

But just how many lions are left in Africa? The answer is surprisingly fuzzy. The most commonly cited estimate is 20,000, but many lion researchers aren’t entirely comfortable with that number.

It’s “based largely on guesswork rather than science,” says Nic Elliot, a lion researcher at Oxford University. “We just don’t know how many there are in Africa.”

Lions are difficult to count because they have low population densities, are mostly active at night, blend in with their surroundings,