The kingfisher sits motionless on the overhanging branch of a small tree, hunched forward, eyes staring intently through the water that laps beneath it.

A flap of wings, a low-angled dive forward, a splash, then a flurry of wing beats as the bird forces its way up from the clinging water, a small fish clamped in its bill. Once back in the tree, there follows a pantomime of head jerks and beating of the fish's head against the trunk, looking rather like Mr Punch attacking the crocodile. Then a clumsy flip of the head, tilted backwards, and the fish disappears head first down the kingfisher's throat. Having swallowed its prey and presumably deciding that its successful lunge into the water had scattered any other fish that might be around, the kingfisher flies fast and low across the open water to the far shore.

We are at Denaby Ings, a Yorkshire Wildlife Trust nature reserve. In this part of the county, "ings" is used to describe shallow standing water in depressions created by mining subsidence. It is claimed by many as a peculiarly Yorkshire word, and there are many ings in South and West Yorkshire, an area riddled with underground mine workings and consequent subsidence.

Denaby Ings is actually a backwater of the River Dearne. Its shallow water is a magnet for wintering wildfowl, but only until the first freeze. Then most of the birds leave to seek warmer, deeper water, and rarely return that winter. Once the big freeze took place just after Christmas, the water emptied. Now we are favoured by a handful of tufted duck, teal and a couple of pochard. Mallard are present, but the most obvious bird on the water are gooseanders.

Now two groups, each of eight or 10 birds, are tacking across the open water, seemingly manoeuvring against each other. When a particular course brings the groups together, altercations occur, with much splashing and lunging, until, quite quickly, the two sides rear away from each other, only to meet up again later, as each flotilla patrols what it sees as its own territory.