The curve-billed thrasher generally measures 25 to 28 cm (10 to 11 in) long, and is immediately recognized as a thrasher by its long tail and short wings.
It is also recognized for its sickle-shaped bill, almost as long as its head width and brownish black in color.
The body is compact with a large head, short wings and long tail.
However, the tail is short relative to other thrasher species.
The chest is grayish brown with circular brown-gray spots.
The eyes are generally orange, shading to golden in adulthood.
Juveniles are lacking in pale tips, rectrices, abdominal feathers are unkempt and upper parts and chest are washed rufously.

Variations are markedly different with each subspecies.
The eastern subspecies has more distinct spots on its chest, more white along the tips and retraces and obvious wing bars.
T.c.
palmeri has less spotting on chest and tips and less obvious wing bars.
Other examples include T.c.
curvirostre possessing longer wings and a tail than T.c.
oberholseri; T.c.
insularum is paler with more grey than T.c.
palmeri and has more visible spotting on its breast.

One study published in 2003 suggested that curve-billed speciation was due to climate, which could be explained by molt and feather wear.
The same study suggested that the Sierra Madre Occidental acts as a barrier to initiate differentiation within the species.
The curve-billed thrasher generally measures 25 to 28 cm (10 to 11 in) long, and is immediately recognized as a thrasher by its long tail and short wings. It is also recognized for its sickle-shaped bill, almost as long as its head width and brownish black in color. The body is compact with a large head, short wings and long tail. However, the tail is short relative to other thrasher species. The chest is grayish brown with circular brown-gray spots. The eyes are generally orange, shading to golden in adulthood. Juveniles are lacking in pale tips, rectrices, abdominal feathers are unkempt and upper parts and chest are washed rufously.
Variations are markedly different with each subspecies. The eastern subspecies has more distinct spots on its chest, more white along the tips and retraces and obvious wing bars. T.c. palmeri has less spotting on chest and tips and less obvious wing bars. Other examples include T.c. curvirostre possessing longer wings and a tail than T.c. oberholseri; T.c. insularum is paler with more grey than T.c. palmeri and has more visible spotting on its breast.
One study published in 2003 suggested that curve-billed speciation was due to climate, which could be explained by molt and feather wear. The same study suggested that the Sierra Madre Occidental acts as a barrier to initiate differentiation within the species.
Curve-billed thrasher