Can you identify these ducklings?

My mother-in-law was heading to the store yesterday when she saw these little guys walking down our driveway. By the time she returned home they had made it to the lake and were happily eating bugs and swimming around. They proceeded to swim down the bay towards a very shallow area. Unfortunately we watched helplessly as a seagull swooped down to make a snack out of one of them. And so now there is only one...

We have tried to identify them without success. Both the internet and the bird books have little to say about a duck with this kind of facial marking.

There is a pair of small, shy, dark coloured ducks back in that bay but if these were their babies how did they come to be so far from home. If those are not their parents then the mystery remains: to whom do they belong? Can anyone help us figure out what kind of duckling they may be?