I am going to make some critical comments because I think that that is the only way to learn. I am not an expert on water birds so these opinions are just my own.
I like your hummingbird shot best, a very good photo. The dunlin shots are good but unfortunately it isn't a very interesting bird. I think that the other shots are just routine except for the very last one.
First some technical points.
Several of these shots are not really sharp, the Dunlins and the hummingbird being the exceptions. You have an adequate shutter speed so you may be up against the limitations of your lens unless these particular shots are heavily cropped.
Secondly, and this is just for interest because there is nothing that you can do about it, the bokeh in the fifth shot is very poor and typical of some telephoto lenses. Very typical is the multiplication of out of focus twigs especially at the top of the image. I have a Panasonic M4/3 telephoto lens that sometimes produces the same kind of ugly bokeh, but my Canon 100-400 never does (it costs about 5 times as much) .
Coming onto the compositions, IMHO water bird shots either have to be extremely sharp, very well lit shots of a beautiful bird, or you have to bring some other interest into the shot. Some suggestions for other interest:
- the bird can be in an interesting setting with reflections in the water, interesting lighting effects in the water or an interesting background.
- you can try shooting from a very low angle.
- you can try to capture aspects of a bird's life cycle, e.g. mating behaviour, fighting, feeding young, etc.
- you can try photographing them under interesting light, especially at dawn and dusk or backlit.
- you can photograph interesting patterns in groups of birds.
Your third shot, of the green winged teals, just isn't very interesting. The birds and moving out of the picture to the right with their heads partially turned away.
Your fifth shot, also of green winged teal, would benefit from being cropped to get rid of the out of focus twigs on the right and to concentrate on the two birds that have their heads sideways on and in sharp focus. Unfortunately there are too many other birds in the shot either with their heads turned away or out of focus in the background. It would be a much better shot if you just had the two sideways on birds.
The shot of the buffleheads is ruined because most of them are turned away and you can't see their eyes. That is a pity because these birds probably have the most interesting plumage.
The last shot is much more better because the surroundings are interesting and you can see the reflection in the water. It is also a more beautiful bird than the dunlins. Unfortunately it isn't quite sharp enough - it this one highly cropped?
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Chris R