Between 1945 and 1989, the share of ethnic Estonians in the population resident within the currently defined boundaries of Estonia dropped to 61%, caused primarily by the Soviet programme promoting mass immigration of urban industrial workers from Russia, Ukraine, and Belarus, as well as by wartime emigration and Joseph Stalin's mass deportations and executions.[citation needed] By 1989, minorities constituted more than one-third of the population, as the number of non-Estonians had grown almost fivefold.

What period did the amount of ethnic Estonians drop by 61%?