Mallard duck female

I'd agree that the first of the three photos is a male in eclipse plumage. See http://www.npwrc.usgs.gov/resource/birds/duckdist/eclipse.htm for more information. Mallards have two molt phases each year. In late summer they tend to molt many or all of their wing feathers. This inhibits their ability to fly and makes them more vulnerable to predators. As a result, the eclipse plumage helps to camouflage the birds when they are most vulnerable. Within a few weeks they revert back to their breeding plumage. One way to determine if one is looking at a mallard male in eclipse plumage or a hen, is to look at the bill. If it is a yellow, it is a male. If it is mottled the bird is a hen.

First photo shows an eclipse male, but the rest are females.