Identification between a Mistle Thrush (Turdus viscivorus) and a Song Thrush (Turdus philomelos) is relatively simple once you know the key features to look for on each bird. This guide will help you.
Habitats
The Song Thrush and the Mistle Thrush inhabit a variety of environments year-round, including areas populated by humans. As a result, habitat alone is not a reliable factor for distinguishing between these two bird species.
Biometrics
The Song Thrush is a medium-sized bird, comparable in size to the common blackbird, albeit a little smaller. They stand at up to 23cm tall. Notice from the illustration that Song Thrush are quite compact in their stature compared to the Mistle Thrush which has a much more upright appearance. The Mistle Thrush is a much larger bird than the Song Thrush. Their overall appearance is of a more substantial & stocky bird. They stand up to 27cm tall.

Song Thrush
The Song Thrush exhibits a combination of cream, buff, and brown hues. One of its distinguishing features is the cream colored breast adorned with distinctive upward-pointing arrow-shaped spots, which also appear on the flanks. Additionally, the Song Thrush has orange-yellow underwings that are particularly striking when the bird is in flight.

Song Thrushes are known for their foraging habits, often found in hedges and on the ground. Remarkably, they have developed the ability to use stones as tools to crack open snail shells to access the meat inside. These birds are also recognized for their melodic singing, which begins early in the year and continues through the spring, with some singing observed again in the summer. Their song is loud and can often be heard at dawn and dusk. The vocalization of the Song Thrush consists of sequences of phrases, with each phrase repeated several times before moving on to the next.
Song Thrush vocalization:
Jacobo Ramil Millarengo xeno-canto.org
While their song is prominent, their regular call is typically less conspicuous.
Song Thrush call:
Uku Paal xeno-canto.org
Mistle Thrush
The Mistle Thrush shares a similar patterning with the Song Thrush but differs in its coloration. The Mistle Thrush features colder hues, displaying a grayish-brown upper body and rounded spots on a white breast. Overall, its appearance is lighter compared to that of the Song Thrush.
One of the key identifying features is the spot pattern on the breast, which consists of rounded blobs that point downward, unlike the upward-pointing spots of the Song Thrush. Additionally, when in flight, Mistle Thrushes reveal white corners in their tail feathers, further setting them apart from their Song Thrush counterparts. These white highlights are sometimes also quite distinctive on standing birds; as in the image below.

The song of the Mistle Thrush bears similarities to that of the blackbird, characterized by a beautiful yet melancholy tone.
Mistle Thrush vocalization:
Johan Södercrantz xeno-canto.org
The call of the Mistle Thrush is notably distinctive and often conveys a sense of agitation. This unique vocalization can lead listeners to perceive the bird as expressing anger.
Mistle Thrush call:
Francesco Sottile xeno-canto.org