Another of my favourite birds (how many are you allowed?!). When they’re not bobbing up and down in the manner that gave them their name, watch them walk down a rock and under the water of the Wharfe in search of invertebrates. They’re chunky, and not the most graceful in flight, as their wings are designed for swimming, but they’ve got bags of character. They have strong focus muscles in their eyes, so that they can change the curvature of the lens to improve underwater vision, and strong legs and feet so that they don’t get washed away. They have more haemoglobin in their blood than other birds so that they can better store oxygen and stay underwater longer. Their nostrils have flaps to stop water entering, and they have a large preen gland to help waterproof their feathers. I tend to think that their bright white chest gives them away, but it may be to aid communication or to help them blend in with the white water of the fast, shallow rivers they frequent.