Damien Cave of the New York Times has pieced together evidence that the net flow of undocumented migrants from Mexico to the US may have dropped to zero or even have reversed itself. That does not mean that no one is crossing the border heading north, but the flow is considerably lower than it used to be, and may be matched by people heading back to Mexico from the US. Elizabeth Aguilera of the San Diego Union-Tribune has also pulled together a similar story.
The evidence comes collectively from the latest round of data collected by the Mexican Migration Project at Princeton University (which interviews migrants in Mexico about their experience in the US), the calculations of undocumented migration by the Pew Hispanic Research Center, which are based especially on the Current Population Survey, by Border Patrol apprehension data, and by organizations such as the Center for Comparative Immigration Studies at UC, San Diego which regularly track data from selected communities in Mexico.