Mexican and American researchers say that the current decline, which has also been manifested in a decrease in arrests along the border, is largely a result of Mexicans’ deciding to delay illegal crossings because of the lack of jobs in the ailing American economy.

The trend emerged clearly with the onset of the recession and, demographers say, provides new evidence that illegal immigrants from Mexico, by far the biggest source of unauthorized migration to the United States, are drawn by jobs and respond to a sinking labor market by staying away…

The net outflow of migrants from Mexico — those who left minus those who returned — fell by about half in the year that ended in August 2008 from the preceding year. The figures are based on detailed household interviews conducted quarterly by the census agency in Mexico, the National Institute of Statistics and Geography.