The Pelican-- The "How" and "Why" of Bird Migration

By Kentia Kalanaki

​Historical Science Relating to Migration
In the 1660s, The Royal Society of London endorsed the idea that when the birds in their area disappeared seasonally, they went to hibernate in bodies of water. They even drowned several swallows testing this theory, which wasn’t debunked until the 1800s. Now, of course, we know that the seasonal disappearance of our feathered friends is due to the incredible phenomenon we now know as “migration.” 

One observation that caused a breakthrough was “migratory restlessness.” This behavior was observed in many caged birds, as they would seasonally become agitated and fly towards one direction in their cages, seemingly attempting to escape.

Nowadays, we can tag birds and track their locations as they migrate across the globe, allowing us to see the specific distances, flying elevations, and speeds of migrating birds.

Migration is a costly venture; it takes so much of a bird’s time and energy, and many birds won’t survive the route. So, what makes the undertaking worth it? 



Why do Birds Migrate? 
Migration is essentially a search for a suitable environment with resources available. Instead of trying to adapt to extreme seasonal weather, migrating species simply move to an environment with a more suitable climate. Resource availability is also a seasonal issue. For example, during summer, the beetle population in Canada may peak while decreasing in southern California; hence, the swallows will migrate to Canada to seek out more food. The reverse may happen in the winter, driving the swallows back to California. 

Many species of birds have generational breeding grounds which they return to each breeding season. These breeding grounds may not be habitable for the species outside of breeding season however, leading to the migration back and forth to suit the species’ needs. 


How do Birds Adapt to the Journey?
One example of a migration adaptation is the “V-formation” visible in fall and spring skies, mainly attributed to geese.

Figure 1: Geese in front give lift to following geese. (Mirzaenia et. al.)

This formation’s transfer of lift allows the rear geese to expend less energy throughout their journey. However, this means the lead goose will be doing the most work, so the group switches out the lead goose periodically, distributing the extra work evenly. 

Another adaptation is a bird’s ability to sleep while migrating. Birds often must keep flying for 24 hours straight for migration. Many birds slip into a half-sleep to get in necessary rest on the move. They keep one eye open, as only half their brain rests at each time, keeping only enough active to maintain awareness of their surroundings. 


So What? 
With approximately 8.7 billion birds moving through the US every fall, migration is a far-reaching seasonal event that we still have so much more to study. As our technology improves, so does our ability to track and observe birds, leading to more and more migration mysteries being uncovered.