Final answer:
The shape of a bird's beak is an example of a structural adaptation, which refers to the physical features of an organism that enhance its survival.
Step-by-step explanation:
The structural adaptation from the choices provided is B. The shape of a bird's beak. Structural adaptations are physical features of an organism like the beak of a bird, the streamlined shape of a fish, or the coloration of the tropical walking stick, which are all evolved in response to the environment and can enhance survival and reproduction. Hibernation, migration, and camouflage, while they are forms of adaptation, are not structural but rather behavioral or physiological. Mimicry and camouflage, while adaptations, are not structural adaptations but rather mechanisms that give animals a survival advantage over others.