Environment : Notes about your surroundings.

SYMPOSIUM: The Natural History Foundation of Orange County will hold its third annual natural history symposium May 21 in the Nelson Research Building at UC Irvine. The all-day event will focus on rare and endangered species in Southern California.

Speakers will include John Heyning, assistant curator of mammals for the Los Angeles County Museum of Natural History, cetaceans; Dennis Kelly of Orange Coast College, coastal bottlenose dolphins; Ivan Show of Southwest Research Associates, California gray whales; Richard A. Arnold of the department of entomology at UC Berkeley, two endangered local butterflies, and Curtis Horton, director of the Desert Tortoise Lifeline Fund, the desert tortoise.

Also scheduled to speak are Robert Thorne of Rancho Santa Ana Botanic Gardens, rare and endangered plants; Gary Bell, manager of the Santa Rosa Plateau Preserve, bats; biological consultant Michael J. O’Farrell, the Stephen’s kangaroo rat; John Griffith of Griffith Wildlife Biology, the least Bell’s vireo; biological consultant Barbara Massey, the California least tern, and Brian Walton of UC Santa Cruz on recovery of the peregrine falcon.

Michael Wallace, curator of birds at the Los Angeles Zoo, will discuss the use of Andean condors as surrogates for the California condor recovery program.

The symposium is co-sponsored by the UC Irvine student activities office, Sea and Sage Audubon Society and the University of California Natural Reserve System. Admission to the event, which will be held from 9 a.m. to 6 p.m., will be $5 for students and $10 for others. For information, call (714) 640-7120.

SUPERNOVA: Virginia Trimble, a professor of physics at UC Irvine, will discuss supernova explosions at Tuesday’s dinner meeting of Sigma Xi, the Scientific Research Society, at the Saddleback Inn in Santa Ana.

Supernova explosions mark catastrophic ends to the lives of massive stars and some close pairs of stars. Trimble, author of a number of papers on the subject, is chairman of the astronomy section of the Assn. for the Advancement of Science.

Tuesday’s meeting is open to the public, with a 7 p.m. dinner and 8 p.m. presentation. Cost is $19; call (714) 762-2727 for reservations.

VOLUNTEERS: The Natural History Foundation of Orange County is seeking volunteers to assist with computer data entry of the fossil catalogue. Curatorial procedures will be explained. Volunteers are asked to come to the museum lab in Newport Beach on Thursdays or Saturdays between 11 a.m. and 3 p.m. For information, call (714) 640-7120.