Paul Souders/Corbis

Biologist Alejandro Acevedo-Gutiérrez usually studies marine mammal behavior, but lately he's been watching other creatures: human tourists.

While on sabbatical in New Zealand, the Western Washington University scientist monitored visitors to a popular waterfall where groups of fur seal pups rest and play. Overenthusiastic tourists often get too close to the seals, try to touch them, or throw food or objects to encourage them to play and move about.

As the seal pups flee, they are sometimes injured or, worse, trampled to death. But when Acevedo-Gutiérrez's research assistant, his wife, sat on a nearby rock wearing an official-looking orange vest, the number of pestering groups of tourists dropped from 38 percent to 13 percent, even though she didn't tell them what to do.

Nature tourism is on the rise in many parts of the world, and that's a good thing if it encourages conservation and educates people. But increased human traffic and development also take their toll on the animals. Posting regulations to prevent harassment doesn't always make a difference, Acevedo-Gutiérrez says, but the presence of an onlooker seems to trigger people's consciences, compelling them to do the right thing.