A couple of points. Firstly, I am not a professional photographer, so the comments are not from a professional perspective. Secondly, I am hyper-critical, so please do not be too sensitive about the comments. Thirdly, are these taken with a D-SLR, or a point-and-shoot? Here are my comments:
- The crocs - Ho-hum, and nothing special. Very difficult to get great pics of crocs, especially when taking pictures from above;
- Cat - Not a bad effort, but two things, the focus must be on the eye, not the bridge of the nose, and the grass over the left eye spoils it for me; You would get different results from a DSLR and a point-and-shoot;
- lions- Just another happy-snappy - nothing special - time of day would not have allowed for much improvement;
- Impala - nothing special, and again, probably the wrong time of day for photography. Composition OK, but you have very little control over the lighting;
- ellie - Nice and unusual. Keep trying at these unusual pics as often, one will stand out;
- Fish Eagle - again, nice with its prey, but being in the shade, over which you have no control, not too special (special sighting, and a great memory, though);
- Hammerkop - I like this, especially with the back light, but a pity you have lost the legs which spoils it a bit;
- Crane flower - Great, clear and well defined - Nice One;
- Kudu - Nothing special, but keep trying, and keep checking for the right light;
- Ellie - Out of focus, and light not great for taking pics;
- Goose - Pic of the bunch - In my view, Brilliant. Extra special well done on this one
- Leopard - Another pic over which you often have no control over the light. Too far from the subject, so unless you have telephoto lenses on a DSLR, there would have been little you could have done about this.
The fact that you are only 15 years old is a plus, in that you have a lifetime to continually improve, and that you are able to learn in a time when taking pictures does not include the cost of development of film. Take LOTS of pictures when the lighting is more appropriate, like early in the mornings and late afternoons and select the best from those. The difficulty in getting great wildlife pictures will be rewarded when that one special picture is admired and commented on, without you having to ask for it.
Photography is a great hobby, and a lot more difficult than most people believe. You have made a great effort and some of your results show it. Just remember that, no matter how good you become at it, there is ALWAYS more to learn.
I have been trying to take wildlife pictures for over 10 years, and have taken 10's of 1000's. I keep comparing my pictures to those in magazines, and try to learn composition and lighting from others. That is the joy. Most important, have fun while doing it, and never give up trying to improve.