How do we know that a species has definitely gone extinct (as opposed to just being extremely rare/elusive)?
In: Biology
There are a few others like Leopard that are in danger from lack of genetic diversity.
And I remember there are several others that are at a dead end from not adapted to habitat which changed faster than they could adapt.
Capture/recapture experiments can help. Say you capture 10 rhinos and spraypaint a dot on them. Release them, come back a year later and capture 10 rhinos again. Only 1 of them has spraypaint, which means that you capture 10% of the population, and the population is 100.
You can use that tool and some other fancy predictive modeling to track a population over time and be able to accurately estimate the population even when it gets very small.
There is never any way to know for sure, though.
The short answer is that we don’t. Consider the [Coelacanth](https://en.wikipedia.org/wiki/Coelacanth).
> Coelacanths were thought to have become extinct in the Late Cretaceous, around 66 million years ago, but were rediscovered in 1938 off the coast of South Africa.
“A species is extinct when there is no reasonable doubt that the last remaining individual of that species has died.”
[Source](https://www.nationalgeographic.org/encyclopedia/endangered-species/)
We don’t know for sure. The Coelacanth is a fish that was declared extinct 66 million years ago but was rediscovered in 1938. Local fisherman knew of the fish earlier but didn’t know it was “extinct”.
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