This is one from me, shot 3 years ago 1/200 sec - F5.6 - 100 ISO - handheld - K1 - 150 to 450 @ 450 plus a decent crop.

#2 and #3 are superb, #2 just edges it for me for the perspective

Neutral Density filters come in different strengths, the brighter the day, the stronger the filter you'll need and a tripod as the exposure will run into several seconds at least.

You can purchase a variable strength filter as well as a fixed density ones, I'd suggest you buy for the largest diameter lens you have and then use reducing rungs to get down to your smaller diameter lenses, reduces the outlay as ND filters aren't cheap.

Have a look here, just one of many suppliers

I have had more success with the K3iii linked to the 150 - 450 than I did with the same lens on either a K3ii or the K1.

I'm not saying its easy, but with good technique my keeper / sharp rate is miles better, I've not tried anything smaller than a blackheaded gull or mallard as yet, but they've been small-ish in the frame and seen at short notice and both the kit and I have responded well.

hope to try Kingfishers March / April time in a local park where they've been seen regularly.

Superb and agree with all the comments

#5 for me John, lovely light

#1 for me John, superb perspective.

To agree with the above, the BW version for me

Imho the Z isnt for anything that moves anything close to walking pace or above, for landscapes, portraits, still life / macro its excellent, before recommending any sort of kit, I'd like to know the prospective owners preferences and aspirations.

LOL, agree with your first thoughts, why not try shooting something out of your comfort zone ??