My home town!
For birds, you can't beat the "back bay" area in Newport Beach. Ride/walk down Back Bay Drive (it's one way, starting off Jamboree Rd., near Pacific Coast Hwy.) The estuary stretches up past UC Irvine, along University Dr. There are also some ponds off Campus Dr. You can easily drive around to find your favorite spots. There are plenty of bird watchers out in the mornings and evenings.
Bolsa Chica is good too- the estuary between Huntington and Seal Beaches along Pacific Coast Hwy. (PCH)
I'm no bird expert, but this is where they all seem to be.
For general nature and scenics, you can't beat Laguna- either the beaches, the town, or the surrounding hills. The city beaches are nice, as are the beaches at El Moro / Crystal Cove State park, just north of Laguna. There are hiking trails in El Moro Canyon, on the other side of the highway, near the trailer park (world's choicest trailer park, IMO). The best hiking is probably in Aliso/Wood Cyns. Park, which you can access from the top of Park Ave. (left on Alta Vista at the top). This is one of the prime sunset viewing places in the state. I always see interesting wildlife in this park- deer, bobcats, snakes, rabbits, birds. You'll be dodging mountain bikes anywhere in Laguna, but Aliso-Wood has hiking-only trails too.
Perhaps the best hiking bet in Laguna is to contact the Nature Conservancy for their docent-led tours of Laguna Coast Wilderness Park- the huge area west of Laguna Cyn. Rd., stretching all the way up past North Laguna. It's mostly closed, except for the weekend tours, which are a treat.
The Santa Ana Mts.- "Saddleback"- lots of great hiking trails, and not crowded. About a half hour's drive from Anaheim at most. There's a neat little wildlife sanctuary (The Tucker) in Modjeska Cyn. Take a tour, and you'll get advice on flora and fauna, and where to go. It's a big area, topped off by a 5600' peak. The best hiking trail is probably Holy Jim Cyn., which you get to by driving a couple of miles up a gravel road at the head of Trabuco Cyn. Dense, beautiful forest, stream crossings, flowers, etc. Santiago trail is great too, and much easier to get to, though bike traffic can be heavy. There's a spot on Santiago where you're almost guranteed to see tarantulas in late afternoon.
If you can get out to Joshua Tree, you won't be disappointed.
Feel free to email. I've lived there most of my life, and I've explored the heck out of all the trails, for years and years.