What is the defining characteristic regarding the water vole's tail length compared to its head and body measurement?

The tail is usually shorter than the combined length of the head and body

The relative length of the tail is a key identifying marker for the water vole when differentiating it from species like the young rat. Specifically, the water vole’s tail is characterized as being relatively short, typically measuring between 7.5 and 12.5 centimeters. Critically, this measurement ensures that the tail length is invariably shorter than the total combined length of the animal's head and body. This contrasts directly with the rat, which possesses a long tail generally exceeding the length of its head and body. Furthermore, the water vole's tail is notably hairy or furred, distinguishing it from the long, sparsely haired, and scaly tail characteristic of rats.