Part zoo, part nature preserve, part historic site, part composting and environmental education lab, the nature center — recently vulnerable to closure because of city budget cuts — is located just off the E Street exit west of I-5 and overlooks San Diego Bay and the San Diego city skyline. To enjoy this treasure, plan to spend a couple of magical hours at a bargain price in a tranquil, art-filled oasis. The nature center sits on 3.33 acres on Gunpowder Point next to the 316-acre Sweetwater Marsh National Wildlife Refuge, which protects one of the last remnants of rapidly disappearing Southern California coastal salt marsh wetland. This habitat supports both plants and animals native to the region, including many seen in the nature center’s aviaries, aquaria, gardens and trails. Here you’ll encounter fresh Pacific breezes ruffling the low-growing native plants, many about to bloom, which cover the salt marsh and provide habitat to more than 200 species of birds. At the Discovery Center entrance you’ll meet green sea turtles swimming inside a glass tank, almost close enough to touch noses. Inside, children can pet sharks and rays housed inside the “petting pool” exhibit and watch staff feed sharks daily at 3 p.m. In the outdoor aviaries you’ll be able to view nesting pairs of endangered light-footed clapper rails, the center’s mascot, as they twitter around their enclosures readying their nests for a new clutch of eggs. The clapper rails represent the center’s greatest achievement, explains Charles Gailband, who oversees the nature center’s animal collections. About 90 percent of the clapper rails’ habitat has disappeared, he says, leaving only 10 percent scattered in isolated clumps, creating genetic problems. “We breed these birds and release them in different populations and habitats to introduce new genetic lineage and make them healthier,” Gailband says. The center has bred and released more than 200 birds since 2001. Its success spurred the San Diego Zoo’s Wild Animal Park and SeaWorld to join the breeding program, which has helped the species recover from a low of about 400 birds in the 1980s.?Near the clapper rails’ enclosure, Gailband points out a Gadwall duck splashing and bathing in the aviary pond, flapping his wings vigorously to dry off while a blue-billed northern ruddy duck swims graceful, rippling circles and a long-billed marbled godwit and other shorebirds wade in the shallows. On the far side of the walkway, Raptor Row houses aviaries for eagles, hawks and owls, none of which can be released to the wild because of disabling injuries. They sit atop their perches, watching their world pass by. Visitors can interact with staff members as they feed the golden and bald eagles at 3:30 p.m daily. Chula Vista resident Nancy Stinebeck, a “bird crew” volunteer for 2 ½ years, first brings out Hawkeye, a red-tailed hawk, followed by Boo, a burrowing owl, on her leather-covered arm, each bird tethered to a harness. “This is a wild animal, not a pet,” she stresses as she warns visitors to stay back and only admire the birds, never touch them. Hawkeye, she explains, was hit by a car and suffered an eye and wing injury and cannot fly. Only one non-native animal resides at the nature center, where he serves as a living example of why a wild animal should never be kept as a pet and why an unwanted “pet” should not be released in unfamiliar terrain to fend for himself. Verde, a docile and affectionate green iguana, offers a “teachable moment” both for adults and for thousands of school children who visit the nature center each year as part of their science curriculum, Gailband explains. A handsome reptile native to Central and South America, he had been a pet until his caretakers decided to dump him in the nature center’s salt marsh wetland to “live on his own.” A tropical species not adapted to living in Southern California’s cold snaps or accustomed to foraging for his own food, Verde would not have survived long on his own. Now a 10-year resident of the nature center, Verde enjoys basking in the sun or under a heat lamp outside in his enclosure during cooler coastal days and spending his nights cozy and warm inside. The Chula Vista Nature Center is open Tuesdays through Sundays from 10 a.m. to 5 p.m. Parking is free and access to the center is via a free shuttle.  Admission is $6 for adults, $5 seniors and students, $3-$4 children ages 4-17. For more information about exhibits and programs, visit the website, www.chulavistanaturecenter.org, or call (619) 409-5900.