ENVIRONMENT

Good Tern--Join a volunteer cleanup crew Saturday to prepare two islands in the Bolsa Chica Ecological Reserve for the return of the endangered California least terns to their nesting sites. The annual event, sponsored by the Department of Fish and Game and the Amigos de Bolsa Chica, provides a rare chance to see the islands, which are normally closed to the public. Hours are 9 a.m. to noon. Free parking is available at Bolsa Chica State Beach, with shuttle buses available to transport volunteers to the reserve. Workers will then be taken to the islands by boat. Wear work clothes and sturdy shoes.

Branch Operation--Funds to plant trees in Cypress are being sought through the Tree Donation Project. Amounts of $100 to $625 will buy a tree, and each donation will be recognized by a plaque presented by the mayor and City Council. Since the program began in 1991, 120 trees have been planted. The deadline for contributions is April 17. Actual trees cannot be accepted. Information: Patty Bailey, (714) 229-6780.

Rain Gain--Hurricane Nora and El Nino have teamed up to produce a wealth of green vegetation and colorful wildflowers in Baja California. Botanist Fred Roberts will illustrate a talk with slides of the northern portion of the peninsula along the storm track in November 1997 and February 1998. He will speak at a meeting of the California Native Plant Society, which begins at 7:30 p.m. Thursday at the Irvine Ranch Water District headquarters, 15600 Sand Canyon Ave., Irvine. Free. Information: Celia Kutcher, (714) 278-4795.

Take a Flyer--Experts will explain the migration of gray whales during a trip around Catalina Island on March 29 presented by the American Cetacean Society, Orange County chapter. The Catalina Flyer will depart at 8 a.m. from 400 Main St., Balboa. Return time is 6 p.m. Bring lunch, binoculars and a hat. Cost is $40 for adults and $20 for children. Reservations: (714) 675-9881.