It is really difficult to tell the difference between the females of different types of ducks. Like many prey birds the females are are much less colorful then the male is. The reason for this is because the female spends much of her time at the nest. It is to her advantage that she is able to blend in and keep hidden from predators while she is on the nest. Unfortunately, since many have very similar camouflage, it makes it quite difficult to identify what type of duck that it is. My guess is that these pics are of mallards because mallards are the most common duck that we see in this area.