Duck with mucus

by Ashley a
(Trinity florida)

I took my baby pekin duck out of the water he was swimming in and put him in a little enclosed area on my porch to run around and he started spitting up mucus out of his nose and I think out of his mouth too. I have another baby duck too and she wasn't doing that and hasn't yet. They are both 4 weeks old and I just got them yesterday. Are they sick or going to die ?