Tachybaptus ruficollis or little grebe (common name) is going into rest after the sunset.
These ducks move very calmly. Thus the ripples made in the water will be smooth. Sunlight coming from the horizon will hit the ripples at an angle such that shadows are well defined. Since the sun is on the opposite side of the bird, bird also appears dark. I have used the shades of the tree here for dark portion of the image.