سؤال 11 — Academic Reading 11 — Main Idea

Migration allows animals to exploit resources that vary across space and time. Birds may travel between breeding and wintering grounds, while some fish move between freshwater and marine environments. The benefits of migration can be substantial, but so are the costs. Long journeys require energy and may expose animals to predators, storms, unfamiliar habitats, and human-made obstacles. Migratory behavior is guided by a combination of inherited tendencies and environmental cues. Day length, temperature, food availability, and social information can all influence when movement begins. Navigation mechanisms differ among species. Some animals use the position of the Sun or stars, while others detect Earth’s magnetic field or recognize landmarks. Because migration depends on conditions at multiple locations, habitat loss at a single stopover site can affect populations that spend most of the year elsewhere. Conservation biologists therefore increasingly emphasize the protection of connected networks of habitats rather than isolated reserves. Climate change adds another complication by altering the timing of seasonal events. If insects emerge earlier in spring but migratory birds do not adjust their arrival time, the birds may miss a critical food peak.
What is the central idea of the passage?