I like this idea of controling animal populations through birth control. I was just telling my parents about a woman in San Francisco who was catching stray cats, neutering them and rereleasing them. People were upset with her for rereleasing them! They’d have been way more upset if she killed them and they certainly didn’t need all the street kittens she prevented.
One BIG caveat. I think birth control for animals should only be used in situations where humans have encouraged overbreeding. For example, animals that no longer migrate because food is plentiful in human environments. Or stray cats that live out of dumpsters. We’re playing god and we need to be mindful of that!