If you use a save where you have all your other ducks added already, the next ducks to spawn in will be ones from your new DLC. (Just be sure to add your new DLC to the save file before loading it; in your list of saved games, click the little pink duck with the + symbol to the left of the save's name you want to add the new DLC's ducks to.)

If you start a new game fresh, the ducks to spawn in will be a random mix of the ducks you already had and the new ducks which means it'll take longer to get all the new ones spawned in.

Thanks

In the end I went with continue the current save rather than start again so the new 27 ducks will spawn in over time. :)

引用自 Rob T Firefly：

If you use a save where you have all your other ducks added already, the next ducks to spawn in will be ones from your new DLC. (Just be sure to add your new DLC to the save file before loading it; in your list of saved games, click the little pink duck with the + symbol to the left of the save's name you want to add the new DLC's ducks to.)

If you start a new game fresh, the ducks to spawn in will be a random mix of the ducks you already had and the new ducks which means it'll take longer to get all the new ones spawned in.