How can the U.S. birth rate be dropping with all of the Hispanics and even Asians coming over just to have babies in America, after all those babies are American aren’t they? /S
Attempted sarcasm aside, this is an interesting statistical question. The total birthrate includes all the children born, regardless of the ethnic or economic characteristics of the mother. If "Bad People Group X" are having a lot of children, that means the birthrate of "Good People Group Y" is even lower than the general rate suggests.