Photographed as it was drying its wings in a tree, darters are a common sight in the Okavango Delta region. The darter (Anhinga rufa), is sometimes called the snakebird because of its habit of swimming with only its head and neck, snake like, above the water. Unlike many other water birds, the darter's feathers have little oil in them meaning they don't repel water well. This is an advantage for the species as the bird is less buoyant in the water and therefore able to dive for prey more efficiently. The downside is that in order to fly and to maintain body temperature, the bird needs to dry itself out. Hence the posture of the bird in the photo is a frequent sight.
Canon 5D Mark 2 with 500mm lens at F6.3.