Don't just hop out of the car and make a beeline for your subject, for instance. Instead, get out of the car slowly and stand beside it for a few minutes. Then, gradually make your way closer to the shore by walking in a somewhat circuitous route--edging closer and closer. And try to appear uninterested in your subject: never look directly at it, avoid eye contact and try to look at the ground, the sky--anything but the subject. Hesitate every few feet until you're close enough to shoot but not so close that you'll scare off your subject. All animals have a "circle of safety" where they feel secure and as long as you stay outside of that distance they will accept you as a reasonable risk. You can tell the instant you've crossed into that circle because the bird will stop hunting, will pay more attention to you, or may just up and fly away. If that happens, make a mental note of the distance and use that information next time.
Getting close to any wild animals, and shorebirds in particular, is a matter of patience and letting your subjects gain confidence that you are not an immediate threat. In shooting this egret I parked the car about 40' away and was able to gradually move to within less than 10' in under 20 minutes. Once I reached what I felt was the bird's safe zone, I stopped moving and just became a part of the background. I was able to shoot for nearly a half an hour while the egret fished.