Birds migrate to find the richest, most abundant food sources that will provide adequate energy to nurture young birds. If no birds migrated, competition for adequate food during breeding seasons would be fierce and many birds would starve. Instead, birds have evolved different migration patterns, times and routes to give themselves and their offspring the greatest chance of survival.
Of course, not all birds migrate. Some species have adapted to take advantage of different food sources as seasons change, allowing them to stay in one location all year round. Other birds are better adapted to cold climates with thicker fat reserves and better feather insulation, and they can survive long cold seasons while they forage for winter food. For more than half the world's birds, however, migration is essential to stay alive.
Migrating for a Meal
For all birds, one of the principle driving forces behind migration is food scarcity. If all birds were to stay in the same tropical regions year-round, food would become scarce and breeding would be less successful. But as food sources are regenerating in the north each spring, millions of birds migrate to those areas to take advantage of the abundance. As the food supplies then dwindle in the fall, they return to replenished tropical regions.
Migrating for Family
Over millennia, birds have evolved different migration patterns, timing and destinations to disperse around the world to breed, taking advantage of a wide variety of suitable conditions to raising their young. Those conditions can vary for every bird species, and may involve specific food sources, habitats that provide adequate shelter and breeding colonies that offer greater protection than a single pair of bird parents.
• Climate: Birds have evolved different types of plumage to survive different climates, and changes in those climates can affect migration. Many birds leave the Arctic breeding grounds, for example, when temperatures begin to dip and they need...