I had just bought a Fujinon 100-400 lens when the caronavirus struck and we were all thrown into lockdown.
I have spent many hours sitting huddled in layers of clothes with the lens trained on a small bird feeder trying to capture small birds in flight. They are mainly chaffinches, bullfinches, bluetits and great-tits and I have seen a few goldfinches but have not caught any in focus - yet