1. “The annual inflow of unauthorized immigrants to the United States was nearly two-thirds smaller in the March 2007 to March 2009 period than it had been from March 2000 to March 2005…”
2. There has been “an overall reduction of 8% in the number of unauthorized immigrants currently living in the U.S.-to 11.1 million in March 2009 from a peak of 12 million in March 2007…”

How can we try to explain these changes? I gave my take to KUHF but in a nut-shell there are two compelling reasons:

1. The economic crisis: Fewer jobs for migrants -”the unemployment rate for migrant workers without documents of all ages in March 09 was higher than that of U.S. born workers or legal immigrants 10.4%, 9.2% and 9.1%”. Migrants tend to be overrepresented in those industries that have taken a solid hit by the crisis (construction and services).
2. The border is more secure: Crossing the border over the past years has become much more expensive not only in economic terms but also it entails risking your life by crossing through the dessert and being abandoned by a “coyote” 
3. The result: The cost of crossing (in the short run) outweigh the potential benefits of migrating especially since the likelyhood of finding a job is not so good.