You need to sharpen images that you post on the web, compression and size reduction does them no favours.
1 - Bird is bang in the middle of the shot, crop the dead space behind it, and add that to the space in front of it.
2 & 3 - Nice setting, make sure you get the eye in focus
4 - The eye is well out of focus, nothing can be done to rescue this one
5 - Really like this one, could benefit from a bit of a sharpen
6 - Like this one as well, straighten the horizon and give it a bit of a sharpen.
Always focus on the birds eye
Make sure that the sun is behind you
1/250 sec is the minimum shutter speed for static birds, ideally go for 1/500, in flight 1/1000 minimum
An aperture of f7.1 will give a bit more depth of focus, this will improve the sharpness of your lens, and give some latitude for focus error / subject moving.
If the light starts going, open up the aperture before slowing the shutter speed.
ISO set to allow the above settings (Auto if you have a Nikon), do not worry about noise, there is always 'noiseware'
Practice