It’s rare that Americans get good news on immigration, particularly when it comes to illegal aliens. But a new report from the Center for Immigration Studies suggests that the illegal alien population of the United States is falling. And dramatically so.

The number of illegals who vamoosed for the home front, mainly Mexico, is a bit of a shock. Between August of last year and May 2008, CIS estimates, it was an estimated 1.3 million. That was 11 percent of a total 12.5 million, meaning the population of illegals dropped to 11.2 million.

And the reasons for the voluntary southward gush — enforcing or threatening to enforce immigration laws, CIS argues — are hardly a surprise. CIS credits enforcement for two principal reasons: First, the number of legal immigrants is not dropping, and the decline in illegals began before the recent increase in unemployment. As well, illegal immigration increased while Congress debated its ill-conceived amnesty plan last year, but decreased when the proposal was killed. This isn’t to say, CIS reports, that the tough economy has not helped foment the reflux. It probably has. So every cloud does have a silver lining.

In any event, enforcement has improved. Before amnesty was defeated, the Bush administration increased enforcement by fencing more of the border with Mexico. Border Patrol agents now number more than 16,500, double what they were a few years ago, and the number of detention beds for illegals has increased to more than 30,000 since 2000. As well, 426 local law enforcement officers, including those from the Rockingham County Sheriff’s Department, joined the 287(g) program that trains them to enforce immigration laws. Here, those deputies snared about 200 illegals since August. Last, states and localities have passed tough measures to fortify federal immigration laws.

The result was 285,000 deportations in 2007, double the number in 2002 and a level the government should maintain in 2008. After all this, no wonder the population of illegals is dropping.

The CIS report also belies the glib argument that illegals are “here to stay” because they are “attached” to this country. Clearly, that isn’t the case. Enforcement works.

Yet the best news from CIS is this: If the trend continues, the population of illegals in this country will decline by 50 percent in five years. Eleven percent in one year is a good start, and if enforcing immigration laws, or threatening to do so, is causing this exodus, then let the enforcement continue. Indeed, increase it. Again, let the crackdown begin.