Final answer:
Damage to the hippocampus disrupts spatial navigation in pigeons, as this brain structure is vital for memory processes and spatial memory.
Step-by-step explanation:
The question relates to the functions of different brain structures in pigeons and how damage to these structures affects certain types of behavior or memory processes. Damage to the hippocampus disrupts spatial navigation in pigeons. The hippocampus is critical for memory, especially normal recognition and spatial memory, and plays a role in transferring new learning into long-term memory. Damage to the amygdala would affect fear memory and emotional memory, not stimulus-response learning or explicit memory as specified in other options. Based on the given text, the correct answer is d. hippocampus; spatial navigation.