Bank Voles and Field Voles are almost certainly much commoner that these maps indicate. It is, of course, difficult to find these species without intensive trapping. many of the records come from bird of prey pellets, or remains of mammals trapped in drink cans left along road verges. Whether the Bank Vole is really more frequent in north Worcestershire than the south is doubtful - this is more likely recorder bias.
Water Voles have undergone a severe decline both nationally and locally under the twin pressures of the spread of Mink, and the unsympathetic management of waterways - extensive dredging, steep banks, lack of suitable grassy margins and so on. By 2007 they are almost certainly scarcer than the decal maps suggest. A good population is being maintained near Bromsgrove.