Thunderbridge Dike wriggles its way for miles along the valley floor. Its name changes, although it is the same stream. Before the tiny hamlet of Thunderbridge, it is Shepley Dike. After Thunderbridge, it is Fenay Beck, then Round Wood Beck. Somewhere around the point where the Ox Field Beck joins, it becomes the Lees Beck before finally swelling the waters of the river Colne.
Some time in the past, a huge project was undertaken to line most of the banks with stone retaining walls, presumably to reduce erosion of the adjacent pasture. At times of heavy rain, the stream flows fast and furious and its meanders are constantly moving ever outwards. Many of these walls have long since collapsed, leaving a streambed of flat stones mixed with shingle and silt.
This new habitat provides cover for bullheads, stone loaches and, regrettably, the introduced signal crayfish. Regrettably because this species of American origin carries a fungal disease to which it is immune but to which the native white-clawed species is very susceptible. Being larger, it can also prey on the native species when coming head to head.
There is also another alien species of American origin. Mink scats and tracks are everywhere as are remains of their hunting and feeding, a crayfish claw here, the remains of a brown trout there. What I didn't find were signs of water voles, for which I was actually searching. I am putting the finishing touches to a survey commissioned by West Yorkshire Ecology, which seeks to establish as much knowledge of the water vole's status in the county as possible.
Fortunately, West Yorkshire Ecology wants negative records as well as positive ones. This series of dykes and becks is devoid of them. I found little evidence of brown rat, either, and only saw two moorhens along the entire length. It seems the mink have wreaked their usual devastation on the local wildlife.
On a happier note, my progress downstream was punctuated by regular sightings of dipper. Either comically bobbing up and down on a prominent rock, or flying frantically past me, there must have been eight pairs in total.
