Reading Comprehension

Read the passage and answer the question.

Many migratory birds can sense the Earth's magnetic field and use it like a compass to guide long journeys. Researchers think special cells, possibly in the eyes, respond to magnetic information and help the birds judge direction. This inner sense works alongside other cues, such as the position of the sun and familiar landmarks, allowing birds to stay on course even on cloudy nights. Young birds appear to combine an inherited sense of direction with knowledge learned on their first migration, gradually refining their routes as they gain experience over several years.