I captured a Cormoran with a Trawl Net , I don't know if it's supposed to happen (I was at high speed). Once I opened the net, the image of the bird was not visible, just his "freshness". As you can see on the first image, it's in my inventory. Then I was able to put it in my birdcage and feed him some meat. In the birdcage, the bird is still not visible.
1. Get really fast on the sea. Coffee + Cane 2. Equip a Trawl Net 3. Drive on a Cormoran to capture it in the net