How are scientists able to say that a random species is extinct? Did they have to look everywhere?
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Scientists and hobbyists in many places around the world track and report populations of animals. For example, you can track the population of local birds in the US through apps on your phone.
Eventually people stop reporting sightings of a specific plant or animal and they are considered extinct after enough time has gone by. The system isn’t perfect and some animals do reappear, but for the most part once an animal is extinct it is really gone
Cannot look everywhere for obvious reasons. They have to do a statistical evaluation. At some point, the odds of the thing still existing when never seen despite being sought in all the places it likes to live, does lead to a pretty good likelihood that the poor lifeform is no longer in existence. And yet, there is an occasional find of something thought to be extinct for quite some time.
They check not only for the animals, but for feces, bones, and other traces and pieces of evidence that the animal is known to leave behind. They also monitor reports by people living in near the habitat to see whether there are any sightings, as well as populations of known prey.
Scientists are actually proven wrong from time to time when they think a species is extinct only to find some tiny pocket of the planet in which it still exists.
They can’t
It’s literally speculation based on not having seen the said species in its known habitat
Of course, the species could have evolved super intelligence and is now living in an underwater city called Rapture far from human eyes
But most likely lack of sightings means they’re either gone or very few remaining
All science is always “to the best of our knowledge”.
A species can be declared extinct when it isn’t found anywhere for a long enough time that, to the best of our knowledge, it appears to have died off entirely.
Sometimes we’re wrong and we find that species again later! But science is always able to be proven wrong; that’s how we learn.
The Okapi was once considered extinct (and I believe was used on the logo of a charity/organisation for extinct animals? May be remembering that wrong) but was later rediscovered.
The most famous example though is the coelacanth. So species absolutely can be declared extinct and slip under the radar.
Also there’s a lot of reports of some extinct species, like the Thylacine, being sighted from time to time.
Nowadays, we tend to closely observe animals that are close to extinction. Scientists will tag and keep watch of them and generally have a good idea of how many remain. If and when one dies, they tend to know. If they’re aware of the total population and they’ve been observing for decades and watching them die off one by one, they can say with confidence that they are extinct.
For animals that aren’t as closely observed or perhaps live in a larger geographical range, if no animals of this species have been seen in the area for a certain amount of time, they’re classified as extinct.
But if they somehow, miraculously, reappear, they can be moved from extinct to not extinct.
They don’t have to look everywhere. They only have to look in the places you’d expect to find it. Dodos were only found on Mauritius so they didn’t have to look in Belgium to see if one turned up there.
Of course if the animal has a wide range it can be hard to tell. Usually they’ll wait a while before declaring it extinct.
Sometimes they’re wrong and it’s still around but that’s no big deal.
Usually they get declared extinct after no one has seen one in a while.
For example the Bramble Cay mosaic-tailed rat was a small rodent only found on the small Bramble Cay island.
The island isn’t big and the last time anyone saw any of them was in 2009. since then people have gone looking for survivors several times over the years until in 2019 the Australian government and the ICUN in 2015 labeled them as ‘extinct’.
There is a chance that some of the small rodents might still live somewhere but unless on is found they are considered to be extinct.
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