Is it only when you pick it up or handle it? If so I really wouldn't worry about the biting as long as it doesn't go on for more then a few weeks. Just being near them quietly now and then, and talking to them throughout the day will help them calm down and get used to you if it is fear related. I would personally only handle that one if it really needed to be moved. For my own ducklings, I know if they only see me when I have to clean/change water/add feed then they have no calm time to understand I am not a risk. I come and go and talk gentle to them off and on then leave. That way they don't get imprinted on me, needing me but learn I am not a threat as well. I know if I am busy and just clean and check and feed they seem to get the idea I am a killer who swoops in causing chaos not as someone who comes and goes without causing problems.
One batch I was busy and I had one duckling that I named Trouble. She drew blood from everyone in my family while she was young. Biting and kicking. Fortunately I only had to handle her for a few weeks till they could be in a better pen after getting some feathers to handle the cold. She mellowed out with age and turned into my best layer. She was also the smartest of my ducks. She would find every hole in the fence, get into everything and was a sassy boss with the other ducks. I believe that she just wanted things her own way and didn't like to be handled or bossed by anyone. I missed the quiet time with her batch as the weather was bad and I was busy and not feeling well and I think that was a lot of the issue with her. Even with the no calm time to get used to me she still mellowed with time and became a favorite of my family. Do try to avoid handling and giving opportunities to bite though. Patterns are a big thing with ducks.
One batch I was busy and I had one duckling that I named Trouble. She drew blood from everyone in my family while she was young. Biting and kicking. Fortunately I only had to handle her for a few weeks till they could be in a better pen after getting some feathers to handle the cold. She mellowed out with age and turned into my best layer. She was also the smartest of my ducks. She would find every hole in the fence, get into everything and was a sassy boss with the other ducks. I believe that she just wanted things her own way and didn't like to be handled or bossed by anyone. I missed the quiet time with her batch as the weather was bad and I was busy and not feeling well and I think that was a lot of the issue with her. Even with the no calm time to get used to me she still mellowed with time and became a favorite of my family. Do try to avoid handling and giving opportunities to bite though. Patterns are a big thing with ducks.