Question

Many bird species that are common in the northern United States during spring and summer fly south in the fall to over-winter and feed in Central or South America. In the spring, they return to the northern United States to breed. Why? There must be some benefit to this behavior! Consider behavioral ecology - what questions would you need to ask to determine proximate causation for this behavior? What questions would you need to ask to determine ultimate causation for this behavior?

Each of you should develop questions to help determine both proximate causation and ultimate causation for this behavior - one question per behavior for a total of two questions each

Answer 1

Many nesting birds in Canada and the northern United States fly south to the tier of states along the Gulf of Mexico where the winter climate is more favorable and food is abundant. More than 300 species of birds that nest in the United States and Canada migrate to the West Indies or Central and South America. The principal wintering area for Neotropical Migrants extends through Mexico and Central America to Panama; it has the highest density of winter bird residents in the world.

This is called migration. Migration is the cyclic or periodic travel of an animal as it returns eventually to its original place of departure. Migration is often annual and is closely linked with the cyclic pattern of the seasons. It is most evident among birds, which have a highly efficient means for traveling swiftly over long distances. The migration of most birds is a yearly cycle.

There are a number of explanations for migration. (1) Birds migrate to areas where food is more abundant, (2) there is less competition for nesting space, (3) the climate is milder, or (4) the daylight hours are longer. These enhance the chances of survival of a bird and its brood. Most birds require a rich, abundant supply of food at frequent intervals because of their high metabolic rate. Adequate food is not available throughout the year in most regions. North American birds must endure the hazards of winter or migrate to more friendly climates. In winter they migrate to the warmer, southern regions of the United States, Caribbean, Mexico, Central America and South America where food is abundant. In the spring, these birds fly north to habitats where spring and summer provide more food production and less competition for food and nesting sites than in their winter habitat. Summertime at northern latitudes also means more daylight hours to seek food for themselves and their nestlings.

external factors prepare birds to migrate?

The pituitary is influenced by environmental factors such as day length and the intensity of the sun. The pituitary responds to increasing day length in springtime by accelerating the development of the gonads and all other metabolic processes, including the development of the thyroid, to prepare the bird for migration.