Thanks for the comments, guys.
@BRASH, yes, they're quite heavy crops which partially explains the softness, but despite the highish shutter speed I suspect there might have still been a bit of motion blur there too. These are both very active little birds. I still thought they were worth posting though. Point taken about central framing. I should have noticed that, but I won't reframe them now as it'd mess up the relevance of your comments.
Cheers,
Mike.