I’ve been thinking about this a lot lately as one of those niggling thoughts we all get: what species were once incredibly common, but are now extinct or critically endangered due to humans? I know some of them – passenger pigeon, Carolina parakeet, American chestnut (which isn’t extinct yet, but is critically endangered) – but there have to be more, right?
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A much shorter list would be, “Which species have INCREASED due to humans?”
Although, to be fair, many species were never incredibly common. They say in the tropics that, “Common species are rare, and rare species are common.”
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It wouldn’t be that short; we’ve domesticated a lot of species, and it’s reasonable to assume many of them wouldn’t be nearly as common without us. Plus our various parasites, and the parasites of our domesticated species, et cetera.
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One animal whose numbers are on the rise is actually the Peregrine Falcon! Because of are cities, their population is going up. They use tall buildings like the cliffs from the wild, and in cities, the population of food is always high, with Pigeons and Starlings making a large chunk of their diet.
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Adam’s right - human action has made a relatively small number of species very common (cattle, wheat, rice, brown rat, etc.) and greatly diminished the number of a much larger number of species (plants, animals and fungi associated with tropical and temperate forests, natural grasslands, savannas, marshlands and drylands), through replacement of native vegetation with cropland and pasture, logging, hunting, introduction of invasive species and other activities.
There are 1,000-2,500 domesticated plant species and only about 40 of domesticated animals.
On the IUCN Red List, which covers only a small fraction of species, not least because the majority of Earth’s species have not even been named yet, there are 2,372 species listed as extinct or possibly extinct and another 10,031 as Critically Endangered. These numbers are massive underestimates, as many groups of species have not been assessed for the IUCN Red List, and many of the undescribed species are likely to be threatened as well. There are 45,321 species currently listed as threatened on the Red List, but the UN estimates that the true number is at least 20 times that.
As to how many of these species were once “common”, it depends on how you define common. When the Atlantic Rainforests of Brazil - where I live and work - were still standing, even a low-density species would have had a large overall population because there was a large forest area. Now that approx. 90% of the original forest has been cleared, we can expect that many of the original species have declined accordingly, and the same is true in many parts of the world. In the past, many forest interior species would have been common, because there was lots of forest. Now, many of them are rare, because what’s left is degraded and fragmented.
Looking just at birds that occur(red) in Brazil, in the past few decades, the following species have been driven to extinction or are possibly extinct:
Cryptic Treehunter Cichlocolaptes mazarbarnetti
Alagoas Foliage-gleaner Philydor novaesi
Eskimo Curlew Numenius borealis
Pernambuco Pygmy-owl Glaucidium mooreorum
Glaucous Macaw Anodorhynchus glaucus
They were once sufficiently common to have persisted through climatic and other changes over many thousands or millions of years. Still others are extinct in the wild, because of human activity, or not yet listed as possibly extinct when in reality they probably are.
The big numbers are a bit numbing, but every species has its story, and you can access more information about threatened and extinct species here: https://www.iucnredlist.org/search
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I’d say the European bison was once pretty common, but now it’s critically endangered in some countries (in Romania for sure). The bearded vulture is no longer breeding in Romania since 1927 and I think that this will unfortunately heappen again in some countries with other species. In iNat the European stag beetle is marked as ‘near threatened’ but I’ve seen lots of them so I don’t think it’s no longer threatened in Romania 
There’s been debate about the impact of climate change vs. humans in the extinction of megafauna in the last 50,000 years but it seems like the current consensus is that humans were primarily to blame. Except in Africa where the impact was reduced by having evolved together, the arrival of humans led to the extinction of megafauna (e.g. mammoths, ground sloths, giant kangaroos, etc.) on every continent.
A more recent example that not many people know of is the Eskimo Curlew, which used to breed between Alaska and the Northwest Territories and winter in Argentina. The population must have been huge since apparently around 2 million were killed each year towards the end of the 1800s. In addition to hunting, during their spring migration they were likely reliant on feeding on Rocky Mountain Locusts in the western US, which were themselves driven to extinction by agricultural clearing.
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Rough green snakes. I know they aren’t endangered, but because of pesticides, they are getting pretty rare to find. It honestly really sucks.
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