New wetland

This area has been turned into a wetland. Many weeks, many people, many trucks etc and suddenly everything left, it was finished. I thought it was going to be a new subdivision, but no, it has walkways, bridges and lovely seats. Lots of planting natives and some well placed larger trees. I sat this morning briefly to just look. It’s only been finished about 2 weeks. This morning I saw / counted 4 black swans, 8 pukekos, a pair of Paradise ducks, many swallows catching insects, and 4 Pied Stilts. Multiple ducks arrived too.
In the city, how did they all know ? It is a lovely peaceful place and about 3 minutes from my home.