Mallards or something else? (Wildfowl Pond)

esther cooperman

Hi all,

I was at the Wildfowl Pond in the Arboretum today and saw two identical looking mallard-type ducks.  Both were mottled brown with a prominent black area at the base of the bill and also prominent white tail feathers.  The photos, after the fact, also revealed a dark stripe going down the back of their heads, although I didn't observe this in person.  Are these just mallards, hybrid mallards, or something else?  Two photos attached.  Sorry for poor photo quality, they were taken with my cellphone. 

Esther Cooperman
San Francisco