Better find a hole to crawl into if you don't want to take part in Earth Day 2000. Organizers expect the multitudes celebrating the 30th anniversary of the original Earth Day to be half a billion strong, from the throngs planning to gather in Washington and Hong Kong to countless individuals ready to join in via the Internet. The theme is finding solutions to global warming: cars will be banned from some streets in Rome; Mexico City will send 30,000 students out to plant seedlings (new trees soak up heat-trapping carbon dioxide); and the Earth Day Energy Fast campaign, based in Los Angeles, will urge folks to shut off appliances for 24 hours. For a rundown on events, visit www.earthday.net. But saving the planet obviously isn't a one-day proposition. Here's a sampling of how grass-roots groups plan to keep the faith even when April 22 is just a memory:

Biker Chic

www.bike.org.il/taba

It's easy to mistake the last Friday of every month for Mardi Gras in downtown Tel Aviv. That's when 100 cyclists ride through the streets, some wearing carnival shirts, wigs and clown outfits. The bikeathons, organized by activist Emily Silverman, try to draw attention to the Israeli city's polluted air. In response, city hall has approved the group's plan for 16 miles (26 km) of bike paths, which will cost $9 million to build.

The Bus Without Wheels

www.greenestcity.org

There was a time, even in wealthy countries, when lots of kids didn't need an SUV or a big yellow bus to get to school. In a throwback to simpler days, Canadian activists are touting "the Walking School Bus", a pollution-free mode of transportation that requires only two legs and an energetic spirit. The Greenest City, a Toronto group, encourages children from the same neighborhood to walk to school together—with one adult chaperone for every four kids. Forty schools have signed up so far.

Going Batty

www.bats.org.u

The creatures of the night have found some friends in Britain. Nearly 100 bat groups are monitoring and surveying the 16 species found across the country. Volunteers can become licensed bat inspectors, organize bat watches and nurse those that are sick and wounded. They can also visit bat roosts and educate leery homeowners about how to fix their roofs or lay insulation without harming the animals.

Calling all Cranes

The relationship between Japan and cranes has been a strained one. World War II disturbed their natural habitats, and the subsequent decline of the country's wetlands kept the birds away. But now a group on the island of Shikoku aims to woo them back. The Kanonji Society to Call Back the Cranes is promoting cleanup efforts and raising money to preserve crane habitats. The group also plans to broadcast crane sounds at volumes loud enough to attract any of the birds flying overhead.