Kane'ohe Marines yesterday got a chance to churn up some mud at Nu'upia Ponds Wildlife Management Area adjacent to their base. In a program that began in the early 1980s, the Marines drive their amphibious assault vehicles through the mudflats every year, helping to break up weeds and open habitat areas for the endangered Hawaiian stilt. All that driving also helps control invasive pickleweed ground cover that could crowd the birds out of their nesting areas. Plus, Marines say, it's a lot of fun.