There are occasional photography workshops at WWT Slimbridge, though they tend to be for the younger photographer. I'm not sure what other reserves do but it may be worth looking on their web sites.
My earliest 'training' in photographing fast moving arial objects was at airshows in my teens. Learning the art of incident light metering, manually focussing with minimal dof and tracking an object doing a well over 100mph to keep it steady in the frame while shooting Ektachrome which at that time was about maxed out at 125 ISO so shutter speeds were not spectacular. Oh yes, and manual wind so you only got one shot in usually.
The great thing about incident light reading is that you can remotely estimate the light falling on an object - when I could afford my first camera many years later with through the lens metering I switched it off for such occasions. If the aircraft was dark camouflaged or polished metal the exposure was generally right whatever as your meter wasn't being fooled in the same way a reflected light meter is. Much the same with the undersides of bif.
Everything else came down to practice, such as being able to operate all the manual controls without looking, accurately tracking focus on a fast moving object and locking part of the subject on part of your focussing screen by panning very smoothly etc.
You got many hundreds of photographers at these events all doing the same thing - it was the norm.
Bird photography is a bit different - most birds don't fly in straight lines for a start, but the answer is the same - practice and take lots of photographs. Personally I shot anything and everything from the Veteran Car run in early November to Weddings, historic visits i.e. Royalty inspecting something, landscapes for calendars, stage photography, my children, passport photos, lab experiments - you name it, and still had time to watch birds, motor racing, party (essential) - whatever.
Practice on blackbirds, blue tits, robins, collared doves - they may be common but trying to catch them in flight is more challenging that a high flying raptor in many ways - you can scrap all your failures these days without it costing anything than your time and eventually you will start to get the odd really good picture.
Simply don't put your camera away, make it part of your life. I tended to use small cameras - Olympus OMs and XAs for many years as they were reliable, small and light with excellent lenses and by then film speeds were slightly faster, even mountain climbers like Chris Bonnigton used OMs - half way up the Eiger every ounce saved was important - you had only one camera and it had to work under conditions that killed batteries. They also had to be good enough to be published to provide funding for such jaunts.
I devoured photography books, knew a few pros and simply shot everything until I got good. I even used my first slr a Practica Vf to deflect a champagne bottle someone threw at me - it survived (with a crease in its top plate) and so did I.
If you want to be a good pianist you practice and for a relatively short space of time you get obsessed and then it is fun and you can get on to the next thing in your life.
Really photographing anything and everything cross pollinates your skills.
It also probaly helped that watching telly or anthing really, bored me and out wanted to be out there in the thick of life living it. It was fun while it lasted and luckily for me it lasted a long time.