I'd start with Tv mode, 1/1600 or 1/2000 s and Auto ISO. For birds on the shoreline, drop to 1/1000 s or so. Use your maximum frame rate (6 fps, IIRC). The camera will keep the lens wide open and raise the ISO as needed. If you are good with processing RAW images, you can get better noise reduction with DxO Photolab or PureRAW than the camera will give you (1-2 stops less visible noise, in my experience).