Why and how do Ospreys and other birds migrate?

The Osprey is a long distance migrant.  Most winter well south of the Mexico border in Central American and in Chile, Argentina, and Patagonia.  In spring, Ospreys may reach the Middle Atlantic States in March.  In the fall, they begin to head south during the latter part of August.  Ospreys are graceful fliers that seem capable of finding lift when other birds cannot.  They will rise almost twice as fast as other hawks and will begin their glides much earlier.  But Ospreys are content to move leisurely between thermals.

An obvious answer to why Ospreys and other birds migrant is simply to follow the seasons, avoiding harsh winters and seeking milder weather conditions, better food sources, and nesting locations.  But many factors may, in fact, initiate the urge to migrate such as a combination of changes in day length, lower temperatures, and changes in food supplies.   Genetic predispositions may also be at play.  Birds that are permanently kept in cages have been observed to go through a period of restlessness each spring and fall, fluttering back and forth inside their cage.  This condition is described as “migratory restlessness” but varies with difference species of birds as does migratory patterns.

The secret to birds’ amazing navigational skills is something of a mystery, partly because birds combine several difference senses when they navigate.  They get compass information from the sun, the stars, and by sensing the earth’s magnetic field.  They also get information from the position of the setting sun and from landmarks seen during the day.  Birds even seem to use their sense of smell, at least for homing pigeons.

For any bird, including the Osprey, taking a journey that can stretch several thousands of miles is a dangerous and arduous undertaking.  The physical stress of the trip, lack of adequate food supplies along the way, bad weather, and increased exposure to other threats all add hazards to the journey.  Also, manmade structures have added to the growing threat to birds.  Many species are attracted to the lights of tall buildings and millions are killed each year in collisions.

So it is a wondrous sight to see throngs of migrating birds pass by, but you should know it is a dangerous journey that they are on.

(Sources: Hawks in Flight by Dunne, Sibley, and Sutton; The Cornell Lab of Ornithology)