The Nikon P900 or P1000 are great for distant birds. For an expert who uses a bino and can easily ID birds from their voices, such a bridge camera can be a fine tool - to get ID shots and some wader watching. I might replace my 2.5 kg heavy "wader solution" by a dedicated long-distance bridge at a later point.
However, the Sony RX10 iv (or my V2) can shoot birds in flight. Which matters a lot for less experienced birders like me. I want to see the pics of a migrating Honey Buzzard on the screen. Or other birds not breeding here. On a coast trip I saw 14 new species, mostly in flight. And BIF becomes addictive once you started it... So for me the Sony RX10 iv is surely a tempting camera. Its price has already come down a little: Euro 1,250 (apparently grey imports).
I've seen an
informative review by trustedreviews.com ("Even with erratically moving wildlife, the camera does a remarkably good job.") which recommends: "I found it performed best by setting the camera to wide-area AF mode, allowing it to first identify the moving subject, and then track it."
The cameraergonomics site writes about BIF settings:
But for birds in flight with clear or cloudy sky in the background, which by the way the RX10M4 can readily handle, [Wide] is better as the bird will not always be behind the AF Area box. For BIF with a busy background such as trees, I need to do more research. As they say in the movie….it’s complicated.
Back to this thread and one of the most instructive posts above:
I'm still getting used to it though and need to find settings that work. But overall i'm happy with how most have turned out, it's a big improvement on the SX60 but i guess you'd expect that anyway.
https://www.flickr.com/photos/charlesbeams87/
These examples by Chris Small are some of the best I've seen so far from the Sony. Shore birds like a ringed plover, turnstone or redshanks are not large and also fast flyers. Of course, this shooting situation is not the most challenging - birds sailing along the coastline, parallel to the camera, no trees.
Jacek's question refering to more problematic BIF situations is partly answered
by this user report from August. Quote: "But when the bird is coming towards you, this is where RX10 IV shows its weakness."
It's fair to say, however, that every camera is struggling in this situation...