This is a side mission that unlocks. After speaking with Howard on a rooftop, you will be tasked to locating his missing pigeons, and your map will be updated to where to locate each missing pigeon.
You will need to get used to swinging around the city and how to be quick.
These missions can be a bit tricky, as you have to grab the pigeons as they fly around the city quick. If you're too slow, they'll fly away and you'll have to return at a later time.
Pick up speed and once you're close enough to the pigeon, you'll need to press LB+RB to catch.
After catching all of the pigeons, you'll unlock this trophy.