There are 6 unlockable animals in Idle Arks: Build at Sea. They need to be rescued in each chapter. Check the map to know the location of the next animal. Under discoveries, you will see a list of character and animals that can be rescued from the current chapter.
Each animal has a special anility. Chicken lays eggs which produce wood, a tortoise grants 20 percent increase in production of all buildings.
Once you rescue chickens in chapter 2, you will start obtaining wood from the eggs laid by them. When a chicken lays an egg, a crew member automatically goes near it and hatches it to get wood. Chickens lay eggs regularly, but it will take some time to lay one. The tortoise can be rescued in chapter 3. he will swim close to your ship and increase wood production boost of all buildings.
There will be multiple locations on a map. To move to the first location, complete all building and upgrade tasks mentioned on the notepad menu.