Thank you Gordon for your appreciation and complement. In fact, most of my photos are only of mediocre and I simply intend to invite other to share their works on the Forum.(拋磚引玉.)
For the Terns in Sai Kung, they are, indeed, fast moving with erratic flying path that making difficult to capture sharp image and I may disappoint you that I actually also a beginner with no special tip for taking the photo of the flying Terns.
As most photographers, I use the continuous AF mode in my camera and usually track the flying bird 1 to 2 sec before fully press the shutter to capture the image. But, in many occasions, my camera or lens cannot be fast enough to capture a sharp in-focused image and the photos I posted on the Forum may the only successful shots after hours of laborious shooting.
From my experience, it would be more easy to obtain better images on sunny day and I usually visit the Sai Kung Pier around 3p.m. to 5p.m. as the direction of lighting is better.
The Terns, though erratic in movement, they are plenty in number and their action are always repetitive and not too difficult to predict with patience and time.
With your prime lens and advanced camera, I believe you can explore different AF modes of your camera to identify an effective way to capture better image and share it on the Forum with us.
Best regards