Does anyone else > 40 years old remember there just being lots more animals around when you were a kid? I don't know if it's just age blinders or paranoia, but in particular I remember there being way more birds pretty much everywhere.
However, no one I asked had seen a horned toad or armadillo in years. And these are definitely the kind of folks that used to. Cicadas used to deafening on summer evenings, but now they were barely audible. Sample size = 1, but the numbers seem to bear out these anecdotes too.
It's totally possible for both of these to be true. Pollution can go down at the same time that animal populations are suppressed for some other reason.