While lawmakers debate measures to reduce the number of undocumented immigrants on Long Island, something unexpected is happening: Some immigrants are leaving, not because of legislation, but because of the economy.

By the dozens, and possibly by the hundreds, immigrants are moving to the South, and even back to their countries in Central America. That, at least, is the conclusion of academic experts, church workers, contractors and the immigrants themselves.

Precise local numbers are difficult to compile because undocumented workers live in the shadows, eluding census takers, landlords and others. But from Glen Cove to Greenport, some of those shadow inhabitants are missing ....