Until 1980, high birth rates and declining death rates led to a large difference between birth rates and death rates results in higher rates of population growth .
Since 1981 birth rates also started declining gradually resulting in a gradual decline in the rate of population growth .
there are two types of migration internal(within the country) and international (between the countries )
Internal migration does not change the population of the country,but changes the distribution of of the population within the nation ( cities ,towns , villages ).
Migration is an important determinant of population change .I changes not only the population but also the population composition of urban and rural populations in terms of age and sex composition.