Breeding·Great Mission

After the vernal equinox in March， the daytime will be longer， and the temperature will be higher. Most migratory birds will live through the winter at low latitudes， breeding at high latitudes. Take the northern hemisphere where most birds live as an example， in the summer of the high latitudes northern places， plants and insects are rich and concentrated， which brings the birds enough food for themselves and their babies. Meanwhile， the long illumination time give the birds enough time to breed their babies. Compared to the southern places， the climate there is milder， the competitors and enemies are less， which are all good for breeding. in autumn and winter， the climate in the north turns harsh， the plants die or begin their dormancy， the survived insects also hide and begin dormancy， most of the rivers froze. The short of food make most birds unable to resist the severe coldness. Therefore after the breeding season， many birds prepare for the autumn migration， they will fly to the south and live through the winter there.

Navigation·Outstanding Ability

The most fascinating place of the birds migration is how to return the original breeding and wintering ground accurately. Birds living in tree holes like mandarin ducks will go back to their original tree hole and breed babies almost every year. Some birds like swifts， their young birds fly to the south earlier than the grown-ups. The young birds could fly to the wintering ground without their parents companies， they can fly back to their born places the next spring accurately. It means that the migratory birds must have good abilities of orientation and navigation. The study of birds shows that the birds abilities of orientation and navigation are various， but the five main aspects are： 1， topographic feature， 2，the stars location， 3， the sun and projection， 4， the magnetic field of earth， 5， the flavour.

On The Way·Full Of Danger

The migration of birds is not only a great travelling， but also a journey full of hardship and tragedy. Most birds confront not only the bad weather， climate， the enemies， but also the impact of human activities. The cats abandoned or free-ranged by people may kill the birds rest in the cities and the suburbs. In America， the feral cats and free-ranged cats have become the main killers of wild birds. Some birds in migration will run into the high buildings， wires and windy generators， the striking are always deadly. The windy generators are always on the way of the birds， in the gorge of California where the generators are installed， about 4700 birds are rolled in the cyclone formed by the working generators every year， they are finally gibbeted by the blades. Otherwise， in many districts， people will hunt the birds on the way during the migration seasons. The larger threat caused by people is the overdevelopment， which breaks the birds habitats， the birds cant replenish energy before the migration， they could find the fitting rest places， wintering grounds and breeding places more and more hardly.