Why do birds migrate ? And where do they migrate to ?

Why do birds migrate? Birds migrate to move from areas of low or decreasing resources to areas of high or increasing resources. The two primary resources being sought are food and nesting locations. ... As winter approaches and the availability of insects and other food drops, the birds move south again.

Explanation:

Birds can migrate for MANY reasons, but most generally it’s when a specific season hits and they move to a place with better weather that’s more  suitable for them. It can also be mating season- some birds have breeding grounds. As to where they go? Way too broad, it depends on where they’re from and why they’re migrating. But they generally move from a cold place to a warm place or to breeding grounds.

the present continuous is a verb tense which is mainly used to indicates that an action is in progress at the moment of speaking.  

it is formed using: person + verb to be (am/is/are) +verb + - ing form  

example: i am studying at this moment .

in addition, the present continuous is also used in order to express things that will or will not happen in the near future.

example: i am having dinner with some friends tonight.

the speaker sometimes   uses it   to express that an action is repeated and it causes irritation on the part of the speaker

example: my sister is constantly complaining about everything.