Wildlife and bird photography doesn't have to cost the earth. I'm not familiar with the equipment you use Keith but I've recently sold a D7200 and Sigma 150-600 for £800, a combo that proved its self worthy of competing with higher end, more expensive equipment. time and time again.
Assuming you're on your way to using correct settings, exposure, ss, ect, technique is the next thing to master.
The reference to using a shotgun earlier in the thread isn't that far off the mark, two of the most important techniques apply to using both, getting on the bird quickly and keeping the camera moving through whilst panning.
Where to start? Have you got any binoculars Keith? If you have, focus your eyes on an object, lets say the top of a fence post. Without taking your eyes off the post, bring your bins up, the post top should be in the bins. Practise this at different distances until you feel you're getting it right 90% of the time.
Next, do the same with moving objects, start with something easy. If its possible, stand at distance, 90 degrees to a road, pick up a car with your eyes, bring the bins up without taking your eyes off it. The car should be in the bins.........do you see where I'm going with this
Start trying it on birds, if you can quickly get on a bird in flight with binoculars, you're on your way to doing it with the camera. It takes practise, it'll come easier to some than others but it does work, I've been using the technique as long as I've been shooting BIF.
When you do think you're getting it right with the bins, start again with the camera on static objects. Fix the eyes on the subject, lift the camera to your eyes without looking away, what you were looking at should be in the VF. Same again start with large moving objects than onto birds.
Getting onto birds in flight quickly is a must in my book, getting it wrong is frustrating but practise, practise, practise until you feel happy (happier)
Razorbills and Guillemots off the cliffs at Flamborough have to be one of the trickiest, they come from no-where and fly like bullets, I like the challenge and have 100's of photos I'd be more than happy to show, plenty on me Flickr (link below) and a lot were taken with the D7200 and Sigma 150-600c.
So, just to briefly summaries, lock on with the eyes, bring the camera up without looking away from subject, subject should still be in VF
Keith, if any of the above is of help but doesn't make sense just ask me, I'm not the best at putting practical into words but happy to help.
atb, Phil