Very interesting Trev, thanks for posting.
The answer lies in the difference in DoF between these two (click to see in LyteBox)
I have to get them next to each other to compare
When I was regularly shooting birds at a distance, I went this route too (i.e. bridge camera rather than £2,000+ long lens).
Except being a Nikon shooter (for menu consistency), I went with the Nikon P510 instead of the Canon SX?? - this turned out to be a big mistake because the AF on the Nikon equivalent to the SX?? series is truly awfully frustrating to use. Apparently the SX50 and SX60 are nowhere near as bad as my experience.
However, the other thing I found was that the atmospherics between me and the subject can often scramble the IQ too, by how much depends upon the weather.
That said, it looks like the quality of yours are better than I could have achieved, even it had focussed before the bird flew off!
Cheers, Dave