Birds: How Do They Migrate?

Bird migration is a fascinating topic that has puzzled experts for centuries of research and observation. How are they innately able to distinguish where and when they should migrate? Are there differences in migration within the bird species?

Facts of interest pertaining to migration:

• 40% of the world's birds travel between summer breeding grounds and winter areas, a surprisingly low number, at least by my own accord. 
• Every year, the Arctic Tern (pictured above) travels 44,000 miles between Greenland and Antarctica. They are 13-14 inches from its beak to its tail and weighs 3-4.5 ounces. Outstanding to look at the size comparison to mileage in flighting 
• Ruby Throated Hummingbirds can nearly double their body fat a week or two before migration, as do Blackpoll Warblers when they fly for 2,300 miles for 86 hours 

Studies that have explained some migration phenomena include an experiment which concluded that Garden Warblers raised in captivity flew in the same exact direction as their wild, migrating relatives, even though captive birds have no sights of the sky in their lives. This is due to their innate ability to see magnetic fields. Only some species of birds have this distinct quality, the specific reason behind it is still unknown. Other birds use the Sun and stars to navigate, while pigeons may be able to navigate using sense of smell and memorizing odors in the wind. If they end up becoming lost, they can retrace their steps by smell.

Some species must learn migration routes from older birds, some return to the exact same territory each year, some follow pre-programmed routes. 

This picture elucidates different senses a bird may use in it's migration process. 

Migration can be triggered by changes in day length, temperature, food supply, and genetic predisposition. 

Watch the video below to learn more about bird migration. 

 https://www.youtube.com/watch?v=4JUYyMHOHb8

The link below is a map of migration, an interesting anecdote. It depicts the bird travel during seasons of migration. 

https://www.allaboutbirds.org/mesmerizing-migration-watch-118-bird-species-migrate-across-a-map-of-the-western-hemisphere/

Bird migration is still puzzling today, maybe there is a connected world pertaining to the bird species that we have not discovered... It's more plausible to consider genetic predisposition and innate qualities to birds that allow them to migrate when and where they do, but there remains the question regarding some species of how they are able to recognize landing spots and direct routes by solely magnetic fields, smell, or memorization. It is frankly astonishing, not to mention their physical feat in migration periods.