It's likely they're referring to the effect outdoor cats have on bird populations. They're credited with the the extinction of 63 species: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5056110/

The problem is this doesn't delineate very well between the feral and urban populations. While feral cats are enormously destructive to some ecosystems, and irresponsible pet ownership is obviously going to contribute to the feral cat population, it's far less clear that urban domestic cat populations contribute to ecosystem damage in any serious fashion - because far more damage was done when we went and paved over hundreds of sq miles of that ecosystem to build a city there.

These feral cat populations came from what used to be domestic cats, which got out and bred.

Nobody is claiming that humans haven't caused damage to the ecosystem. But you're just spouting a whataboutism when we _know_ that cats are also incredibly damaging when let to roam free.

And rodents (that's rats and mice, you know, the critters cats hunt) with the extinction of 75 species, same source. Maybe it's complicated and pretending that pests and song birds are exactly the same doesn't help?

These data only refer to island ecosystems like Australia. And this is all nonnative species, not just cats. This is entirely irrelevant to the issue of urban and suburban cats in the United States.

"mammals", though?

And lizards.

Cats are especially devastating on island ecosystems where birds, small mammals, reptiles, fish and amphibians have few natural predators. Small mammals such as mice, voles, shrews, moles, bats, pikas, and yes even rats are valuable in ecosystems as an abundant source of food for birds of prey and other predators or good controllers of insects and other things we consider pests. Without small mammals larger predators have a greatly reduced food supply. Plus some small mammals are cute as fuck.

  Cats kill mice.

https://en.wikipedia.org/wiki/Toxoplasmosis