The situation is definitely quite complex. In general terms, it's best to make sure that the right conditions exist for a healthy biodiversity. Specific species will then colonize the new habitats, a process that can take many years for some species, depending on many factors.

Of course, I'm not averse to helping nature on her way, so I'm all for digging ponds, planting shrubs and trees, and you name it. Also, measures such as fauna tunnels are often absolutely necessary to connect various habitats with each other -- and fences alongside roads to spare critters a terrible death. To be honest, drastic measures will not rarely be needed to (for example) get rid of soil very high in nutrients, or to undo canalization to streams and rivers, et cetera.

I'm generally with you on the native predator approach, although sometimes the solution turns out to be worse than the problem. There have been many disasters.

If only there was a good method to test this in a smaller lab environment with the results in the wild to mimic those in the experiment.

Sometimes, it's a spectacular success. I like how the introduction of zebra mussels into the waters of Lake Michigan has cleaned that body up. Of course, they now have to clear the city of Chicago's water supply inlets of the little bivalve mollusks regularly because of their remarkable adaptation but it's a small price to pay for clean water.

My fellow Dutch moderator at M&C, Amsterdam has these parakeets, too. No doubt you know. You can't miss 'em (except if you're blind and deaf or stick to The Wallen).

Perhaps they were lovers.

http://www.metmuseum.org/toah/hd/ukiy/ho_JP2453.htm