So, for your best close shots some sort of hidden shooting is the way to go but one can luck out anywhere, anytime, as demonstrated by the fox, provided you have your gear ready like grandpa used to have his gun ready, loaded, standing in the back entrance until grandma blew her top.
This is great stuff, your gear is your barn setup! I don't hunt, but always wondered if hunting techniques would be helpful for this application. See, the issue I have it that my back yard is canopied by tall trees which the birds truly love but also block good light for much of the day especially in the summer time. But I get a few from time to time. The attached pine warbler was taken with my further dismal 5d3 and the first version of the non IS 300/2.8 and a 2x extender while hiding behind an Air Conditioning unit in my pajamas. The robin was one of the first taken with my 5d4 with the same lenses and a 600RT from behind a tall prickly shrub. I think i can park my truck beside a creep myrtle , bait it with food and just quietly sit in the driver's seat with the windows down waiting.
That chickadee shot is just awesome, those things are fast and always needling each other (survival training?), I truthfully couldnt begin to understand how you pulled that off. Thanks for posting the nuthatch, thats one of my all time favorite birds - very admirable in their family structures.