Ranjan i fully agree with Sabyasachi,

to have patient and wait and allow subject to get closure is always a good trick then expect a huge long lens.

although prime is prime but you can do lots of thing even with point and shoot like getting full frame images of birds if you know the subject.

i have some nice full frame small waders who allowed me to get close in just 15 minutes and even some small birds too.

so try to do that thing first and it will help you a lot in getting know your subject from close and you will have nice frames.