Mute Mallard chick?


I’m m lucky to have a natural pond at the bottom of my garden. Every year I have mallards nest and they bring their chicks into my garden. Unfortunately we lose some to predators. This year mum had 10, reduced to 6. Last week we were down to 5 ( we’re talking  chicks nearly the same size as mum). Today a young one came into the garden. I swear it’s the missing chick. It’s not scared of me, but it doesn’t make any noise. It’s beak opens…but nothing comes out? Any ideas please?