Where: More than a dozen sites across the country

What: Earthwatch Institute matches would-be research assistants with scientists who are studying animals and their natural habitats. A volunteer might record the behavior of wild horses on the Outer Banks of North Carolina or tag terrapins off the coast of New Jersey.

Duration: Most trips last two to 17 days.

Volunteers pay: $950 to $2,650, including meals and shelter, which varies wildly, from tents to country inns (EarthWatch.org)