re: Could the argument be made that the chicken is the most successful species of all time?

"The FAO data tells us that in 2018, there were 25.7 billion domesticated livestock birds in the world, of which chickens made up 23.7 billion. Or if you want to use the 1997 figures (so as to compare like with like), you get 15.8 billion livestock birds, of which 14.1 billion were chickens.

The estimate for the global bird population in 1997 ranged between 200 billion and 400 billion individual birds, depending on the method used.

So we can say that, very roughly, in 1997 chickens probably made up somewhere between 4% and 7% of all birds in the world. In 2018, that may have been between 6% and 12% of the global bird population, assuming that the total number of birds (with the exception of the chicken count) hasn’t changed dramatically in the last two decades.

That is still a lot of chickens, but not quite as many as four out of every five birds on the planet."