Bird Migration

"The stork in the heavens knoweth her appointed time; and the turtledove, and the crane, and the swallow, observe the time of their coming.”- These are not just any words but are words written in the bible by Job about migration of birds.

In our backyards, most of us won't see anything like the migrating Whooping Crane, but there's a tiny possibility we might, in certain neighborhood wildlife refuges and parks. Sometimes a bird species that's present in our neighborhood the whole year can also be migratory.

Birds do not migrate because they figure out that they need to. It's been shown that, at least in some birds, changes in day length cause glands in the birds' bodies to produce hormones that produce profound changes inside the birds, changes that prepare them for the flight south. In the fall, as days grow shorter, fat accumulates under the skin. This fat contains energy needed for those coming days when the birds will be spending more energy flying than they'll be eating during their occasional rests. Weather changes sometimes trigger a migration's start, but by then the birds are already prepared. The urge to migrate must be very powerful. Starlings caged as their migration time approaches become extremely fidgety and point their bodies in the direction they want to fly toward.

Watching bird migration take place is one of the most exciting and interesting things a birder can do, and it's something you can see in your own backyard but it is wonderful if watched in the wild while on a safari. Especially in the spring when birds are in their bright courtship plumage and males are lustily singing, it's a pure joy to walk around taking note of which species have arrived. In the fall, as Northern-Hemisphere migrants head back and they are much quieter and their plumage is more drab. They're harder to identify, too. Nonetheless, their passage is still a majestic event to behold.

Birds fly at varying altitudes during migration. An expedition to Mt. Everest found skeletons of Pintail and Black-tailed Godwit at 5000 m (16,400 ft) on the Khumbu Glacier. Bar-headed Geese have been seen flying over the highest peaks of the Himalayas above 8000 m (29000 ft) even when low passes of 3000 m (10000 ft) were nearby. Seabirds fly low over water but gain altitude when crossing land, and the reverse pattern is seen in landbirds. However most bird migration is in the range of 150 m (500 ft) to 600 m (2000 ft). However birds too have their destinations and they just don’t go anywhere.