They say you have to kiss a lot of frogs to find a prince. Still, with more than 6,000 species of amphibians around the world, you might think the odds are pretty good, if you can stand the slimy lips.

But frogs are disappearing at an alarming rate — scientists estimate that from one-third to one-half of amphibian species are in danger of extinction. That's why this year — a leap year, of course — has been designated as Year of the Frog by global conservation organizations. To raise awareness, many zoos and aquariums across the country will be holding events on leap day, Feb. 29.

Internet dating may have replaced amphibian-smooching in the modern search for a mate. But there are many other reasons that the loss of frogs should concern all of us.

"Frogs are really good indicators of what's going on in the environment around us," says Kym Gopt, associate curator of conservation at the Cleveland Metroparks Zoo in Ohio.

Most frogs live both in water and on land at different stages of their lives, as tadpoles and as adults, so they're affected by problems in both types of habitat. And since they take in water directly through their delicate skin, they're acutely sensitive to water quality.

So frogs can be seen as an early warning system of problems that may eventually affect the rest of us. "If chemicals in the water cause mutations and reproductive problems in frogs, think what it could be doing to humans," says Vicky Poole of the National Aquarium in Baltimore.

Frogs are important for other reasons as well. Frogs and tadpoles consume huge numbers of insects — many of which cause crop damage and disease — and are themselves an important food source for many other species. And amphibians are valuable to science in ways that directly affect humans.

"They're important because they've had a huge role in medicine, research and medical applications," says Shelly Grow, conservation biologist with Association of Zoos and Aquariums. "Many medical compounds have been found because of the secretions in their skin or the microbial communities on their skin."

Why are frogs disappearing so rapidly? Like many other animals, they are affected by habitat loss and climate change, as well as pollution. But a special problem is a disease that's spreading all over the world, a fungus of a type called chytrid.

"When this fungus arrives in an area, 50 percent in the area might go extinct within six months," says Grow.

Some species affected by the fungus have been successfully bred in captivity, like the Panamanian golden frog. But fast action is critical if conservationists hope to reproduce this success. Fortunately for the golden frog, Grow says, a lot of research was done before the population was reduced, so zoos had the knowledge needed to breed them in captivity. Other species don't have this advantage.

"The room for trial and error is now particularly slim," says Grow. "We can't take out a few hundred and say oops, that didn't work."

Of course, even if we successfully breed a species, what if their habitat has been destroyed? As Poole says, "I can't go and return a frog to a parking lot."