Thanks - nice. How does this setup cope with e.g. warblers flitting round trees/bushes?
Eye tracking struggles in certain scenes. Trees and bushes, seaweed covered beaches and even short grass at times. The sensor picks up eyes where there are none, latching on buds, nodes or leaves, etc, etc. This is fairly easily dealt with by having one back button set up for eye detect (in my case it's the AF-ON button, because my thumb lies there naturally as first choice), with another (in my case the * button) set up for spot focus. Then, when the camera decides not to co-operate, I go back to the old-fashioned method of finding the bird with the spot focus. Often, once this is done, the camera usually comes to its senses and finds the eye with the eye detect button. If it doesn't, there's still the fall-back of the spot focus to do the job, just like in the old days, although a disadvantage of both my mirrorless models is that the smallest 'spot' available isn't quite as small as the small spot on the 7D II.
One important thing to remember is that in these cases, you need to have 'subject tracking' (which is different to eye detect or Servo focus) disabled, otherwise when you press the spot focus button, you get blue squares dancing all over the place as it hunts for the subject to track. This happened to me the other day with those white-rumped sandpiper shots, after I'd enabled subject tracking earlier in the day for a Caspian Gull on bare sand that I'd been photographing. When I pressed the eye detect button, it found the seaweed around the bird instead and at first I couldn't understand why the spot focus was dancing all over the place, until I realised I had the 'subject tracking' enabled (I normally don't use that function, although it has its uses).
When I first ordered my R5 back in 2020 I lived in hope that it would be able to lock onto the eye of a Sardinian Warbler or something like that, skulking about deep in the twigs of a Spanish shrub. Sadly, when I got it, I realised that this Holy Grail was not yet within reach, but it's still a damned sight better at finding focus than my DSLRs ever could be.
Having said that, my R7 found this Firecrest in a Northumberland bush last November (with, admittedly, some difficulty at times, although I managed 7 keepers during the very brief time it was in view). Caspian Gull shots added from this week, using 'subject detect', which never lost the eye, even before I'd focused.