Thanks Kevin
The pale ones are juveniles, they are probably 3-4 weeks out of the nest at this point. There's an adult ringing the neck of a youngling in the top photo and obviously the last one is an adult as well.
How are you getting on with your new lens?
Ha, yes this is true. Always keeping my eyes open.
You could try a monopod, something light in carbon fibre would help take the weight. It's a bit trickier than a tripod at first but more portable.
That said I found regular use of heavier gear gets you used to the weight. Controlled breathing can also help stabilise your upper body and by locking your elbows into your torso the weight can be transferred into your body rather than being supported by your shoulders alone. Apologies if you already know this.
At 800mm you're at f/9 which is going to make your autofocus work harder if the light isn't great, especially on moving subjects.