What general characteristic is cited as the defining feature of the thrush family breast pattern in many regions?

A pale ground colour marked heavily with dark streaks or spots

The text identifies a commonality shared by many species grouped under the thrush umbrella, which frequently causes identification challenges. This defining characteristic across many regions is the breast pattern itself: a light or pale ground color that is heavily overlaid with dark markings. These markings usually manifest as dark streaks or distinct spots. This widespread similarity in speckling, seen in species like the Song Thrush and Mistle Thrush, is precisely what requires birders to look closely at secondary details, such as the shape and density of the spots or specific facial markings, to achieve accurate differentiation.