Read it somewhere, maybe on FR. Should take better notes, I suppose.
But it seems likely enough. It would be typical for the stage of industrialization and income they've arrived at, in the current environment. It's not like the 19th century, when people kept reproducing out of habit when it was not economically beneficial to do so.
US fertility rate is 2.08; birthrate is 14.14 per 1000 of pop.
Mex fertility rate is 2.45; birthrate is 21.01 per 1000 of pop.
I have seen published the year 2016 as when there will be no more mexicans left to migrate to the US. I think that is early but it will eventually happen.
It has also been said that sometime after that date, the mexicans will begin returning home.
For those that think there are too many mexicans here, just wait until there are not enough.