We might consider it a bad thing to kill for sport, but why is it bad for animals like cats to enjoy hunting and killing other animals? Cats have no such moral restrictions.

No morals were implied or intended. Hunting for sport is unconstrained by population feedback loops.

It’s not about morals. It’s about environmental/ecosystem balance. Parent comment talked about feedback loops and over-hunting.

>It's not even clear to me that birds are a primary food source for domesticated outdoor cats. They might be hunting them just for sport.

This seems like a condemnation of hunting for sport to me.

We must be coming from different places.

I still don't see a condemnation at all. Other than the implication that sport is not constrained by hunger and therefor can have unbounded externalities, which again is not moral, it's a practical observation and concern for bird populations.

Maybe you could pinpoint further which part of the sentence you quoted brings in morality.