I often found that one of the limitations to my wildlife studies was a lack of suitable reference photos. As I had a passing interest in photography, I decided that I would look to fill this gap myself.
My initial forays quickly showed that I didn't really have the right kit for the job - I just couldn't get close enough to the subjects. After doing a bit of research, I've invested in a longer zoom - a Sigma 150-600mm Contemporary. I also found that you will be very lucky indeed to just stumble on a good shot. A better approach is to decide what your after and then plan an approach (location, time, etc) which is specific to the species that your interested in. You also have to be patient - find a suitable location and just sit down and observe what's around you (this is also very good for your mental wellbeing - just being out and about in the fresh air).
I love dippers and so am concentrating on them initially. I have made a few schoolboy errors, but have had some rewarding results already.