A lot of the time when I photograph wildlife at Parker River National Wildlife Refuge I use my car as a blind. Large shorebirds like egrets are less skittish of people than smaller birds, but a good way to get as close as possible is to not get out of you car. I usually find a good spot, stop and turn off the car and photograph through an open window. Most of the time this technique works out well.
Nikon D810, 1/2500 @ f/9, ISO 500, 500mm with a 1.4x teleconverter
Nikon D810, 1/2500 @ f/9, ISO 560, 500mm with a 1.4x teleconverter