When Mitt Romney said months ago that enforcing laws against employing illegal immigrants could lead to "self-deportation" by those workers, many critics scoffed.
But according to a new Pew Hispanic Center study, that may be exactly what's happening.
Mexicans have stopped pouring into the United States, the study says, and the net numbers even indicate that they're going back home. More than half of Mexican-born people in the U.S. are illegal, and Mexicans make up nearly 60 percent of all illegal immigrants here.
Their migration, over 40 years, is the largest immigrant wave in terms of numbers in U.S. history.
Many factors contribute to the reversal of net migration, according to the study, which analyzed government data from both countries. Among them are the weakened American job market, especially the construction industry; stepped-up border enforcement; a rise in deportations; greater danger crossing the border illegally; and a decline in Mexico's birth rates.
The study found that while 200,000 Mexicans came to the U.S. legally between 2007 and 2010, 800,000 who were here illegally left. That lowered the total number of Mexican-born people in the U.S. from 12.6 million to 12 million, the study says.
In Florida, the estimated number of Mexican immigrants decreased from 316,000 in 2007 to 263,000 in 2010.
After hitting a high of 26,400 in 2008, the Mexican population in Palm Beach County decreased slightly but still exceeded 20,000 in 2010, according to census estimates.
"Wherever you look in South Florida, there are fewer Mexicans," said Adan Labra, a native of Mexico, now working for the Farmworker Association of Florida in the farm town of Immokalee.
"We have fewer people working in farm work in Immokalee, and we know that many people who worked in construction in other towns around here also lost their jobs."
Tomato industry changes
The Farmworker Association says the number of farmworkers in Immokalee at peak season has decreased from 22,000 in 2000 to 12,000 today.
Labra, 30, said one reason is that tomato growers have decreased the acreage they plant because it has been harder to turn a profit. Some of the increased competition they are facing is coming from Mexico, which exports tomatoes to the U.S. Some employers that formerly operated in the Immokalee area have moved their operations to Mexico and Central America, Labra said.
"I know some people who lost their jobs moved to other parts of the United States, and I know other people who have returned to Mexico," he said. He didn't know whether the people who picked tomatoes in Florida are now doing the same in Mexico .
Labra also said many other people have been deported because of increased cooperation between local law enforcement and federal immigration authorities.
The Pew Center study appeared this week as the U.S. Supreme Court is weighing whether individual states can adopt their own immigration laws. Arizona has sued the federal government for the right to detain illegal immigrants according to its own laws, claiming that the state has been inundated with immigrants and the criminals who smuggle them and that the U.S. has not done enough to stop that traffic.
David Abraham, professor of immigration and citizenship law at the University of Miami School of Law, said the drop in immigrant traffic also may be caused by a slight uptick in the Mexican economy.
And while the study states that an improved U.S. economy could spur a resurgence of emigration from Mexico in time, Abraham points to the falling birthrate in Mexico as the key factor that could make the current lower figures a harbinger of the future.
Less urgency to emigrate
In 1960 the average Mexican woman bore 7.3 children. By 2009 that figure had plummeted to 2.4 children.
"That's a dramatic change in demographics," Abraham said. "When you have fewer mouths to feed, that leads to less of a need to send someone from the family north looking for work."
He also said more women in Mexico are going to school for more years, delaying childbirth, and have left agricultural jobs for manufacturing jobs, leading to more families bringing in two steady paychecks and creating less need to emigrate.
"There is no question that the flow is going to slow down from Mexico, although they may be replaced by Central Americans," Abraham said. "In fact, we're already seeing that."
The study also found that the number of Mexicans apprehended trying to cross the border illegally fell by more than 70 percent in recent years, from more than 1 million in 2005 to 286,000 in 2011. In each of the past two fiscal years, about 400,000 unauthorized immigrants were deported, roughly 70 percent of them Mexicans.
Families returning to Mexico are in some cases taking their children born in the U.S. who have dual citizenship. The 2010 Mexican Census counted 182,000 U.S.-born children under age 5 living with their Mexican parents in Mexico.
The natives of Mexico, both the 6.2 million undocumented and the 5.8 million here
legally, are by far the largest single group of immigrants among the 40 million people now in the U.S. who were born elsewhere.
The Mexican-born make up 30 percent of the immigrant population. Next in line are the Chinese-born, who make up 5 percent.
"Looking back over the entire span of U.S. history, no country has ever sent as many immigrants to this country as Mexico has in the past four decades," the study says.
Security concerns persist
But the study also says that, compared with other immigrants, Mexico natives "are younger, poorer, less-educated, less likely to be fluent in English and less likely to be naturalized citizens."
Mexicans are by far the largest Latino bloc in the nation, and Latinos as a whole are now the largest minority group in the U.S., having passed African-Americans about a decade ago.
Abraham said waves of immigration have always caused worry among Americans already here, but political parties often vied to win the votes of the new arrivals and tamped down anti-immigrant feelings within their own ranks. He pointed to President George W. Bush and his efforts to try to get the GOP to court Latinos.
But Abraham said he believes worries about security since 9/11 have led many conservatives to take a harder line on immigration than they had in the recent past. Concerns over jobs also have contributed. That has led GOP front-runner Mitt Romney to take a hard line on the immigration issue.
"But it's true that all over the world people have always been afraid at the arrival of foreigners - whether they spoke Italian, Chinese or Yiddish," Abraham said. "Immigration has never been popular. The attitude has always been, 'Close the door behind you.' '
Staff researcher Niels Heimeriks contributed to this story.