Yesterday I noticed one of my 5 week old drakes not walking right and lagging behind the others. It seemed his feet were more outward than under him. Today he didn't even try to keep up on their way back to the barn and I carried him. His feathers look a little ruffled, he's not snuggled up with the other ducks and is listing a little to the left while laying there trembling slightly. Any suggestions?? All the others seem fine.