"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.
