Final answer:
Migratory species are difficult to protect because they move across large distances, require the conservation of habitats along their routes, and need international cooperation for comprehensive protection.
Step-by-step explanation:
Migratory species are harder to protect for several reasons. They don't stay in one place long enough to be effectively counted or monitored. Moreover, specific habitats along the migration routes need to be preserved, which can become complex when these habitats span across multiple countries with different conservation policies and practices. Finally, since migratory species are affected by habitat loss and threats in both their breeding and non-breeding grounds as well as along their migration paths, protecting them requires international cooperation and comprehensive conservation strategies that cover vast geographical areas.