Painting sea birds, or any birds for that matter, is quite challenging, as the colour gradients are really quite subtle, while the colours themselves are distinct and definite for different species of birds. This close-up of the mother duck's head shows what I mean.
Another point of interest in this painting is the rock in the foreground. While we might assume that a rock is just a rock, there are lots of different colours involved in conveying a natual looking rock. And if it is a tidal rock, then we have the added complication of little white and grey barnacles and brassy coloured rockweed. Then we have the water lapping against the rock and pebbles in the foreground.
A natural, tidal beach has a lot going on when we look at it closely, especially if we want to be faithful to getting it to look really authentic in the painting.