I got Dave's raw files and look at the up close
the issue with the first image is that the left merganser is not sharp. it seems the focus locked on the ripples behind the bird. the bird is soft and on top of that it is small in the frame therefore the poor IQ. What focus mode were you using? where was the focus area t the time of capture ?
100% crop from RAW
the 2nd image isn't quite sharp either but the main issue is that it is a HUGE crop. you can see how small the merganser was in the frame, crops like this never make it
hope this helps, since this thread has educational value I am sending it to the ETL forum to add to our resources