For people having issue unlocking this achievement (as I did), you have to find black cats in trees and use the helicopter from a fire station to rescue them.

I couldn't manage to find a single one of them until I tried this solution:

1- Start a new "Paris" game
2- Move all the trees in one area where you can see them all, with enough space between
3- Add a few more trees to fill up the screen (I had roughly 30 trees)
3- Build a fire station with helipad next to the trees
4- Wait for a cat to spawn and send a helicopter to save them (Repeat 5 times)

Note:

- Don't activate the view from above but from the side, it's easier to spot them that way
- A branch with a black cat on it will pop out on the side of the tree
- They spawn in both trees and flower trees
- Once you have saved a cat, the next one will spawn about a minute later

I've attached a picture to show you my set up and how the cats look.