Migration for Survival
Migration is the seasonal movement of animals from one part of the world to another. Many creatures migrate, including butterflies, fishes and mammals, but the most famous migrants are birds.
Birds move to an area to improve their chances of survival, usually because its climate provides a better environment for feeding, or especially for rearing young. There is a corresponding return movement at the end of the breeding season.
Migration plays an important part in the lives of these animals: it is a successful way of adapting to seasonal change.
But there are dangers. Bad weather, lack of food, predators, navigational problems and human interference all take their toll. Although many perish, enough survive to keep the species going. The benefits to the species as a whole are greater than the hazards to the individuals making the long journey.
What are these Benefits?
It is easy to see why an insect-eating bird, such as the Spotted Flycatcher, should leave Ireland in the autumn to spend the winter somewhere in Africa. Such a bird could not survive the winter here. But why should it return the following spring? (This could make for an interesting discussion)
In northern countries, with contrasting seasons of summer and winter, there will be a large but seasonal 'crop' of insects in the summer.
Many insect-eating birds cannot survive the winter in these northern countries and so there isn't a large resident population of birds ready to eat this 'crop'.
Migrant insect-eating birds flying north find this rich crop of insects available to feed themselves and rear their young, without competition from too many 'resident' species.
Because these migrants are seasonal, they may have fewer predators. Specialized predators would be less able to survive the winter in the absence of their migrant prey.
In summer the days are longer at higher latitudes. The further north a bird travels, the more hours of daylight it will have for gathering food, ie it can rear more young.
For birds, with their high mobility, migration is the rule rather than the exception. Most birds move somewhere as the seasons change. For some, such as Swallows or the Arctic Tern, the move is dramatic involving thousands of miles. Others, like Starlings or Robins, may move a few hundred miles into an area where some of their species already live. They look just like the 'residents' and their arrival may go largely unnoticed.
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