The bird has worked great!
The thing I find about oil painting is that I need a stronger idea (even than when working in watercolour) of how the finished painting will look - even before I start the damn thing. As Nick says, the whole thing can get into a right old mess if you just keep adding colour and paint to the mix.
A smallish watercolour (or pref. acryilic) painting as a guide to the ensuing masterpiece, can have huge benefits. Also - make sure that you have all your necessary reference material to hand when making the painting. Just because oils is a medium which allows re-working, doesn't mean you can afford to be wishy-washy about the whole comp. and colour structure - quite the opposite, in my opinion. I have to blend edges into edges when oil painting - and if my 'other' edge is a piece of moorland, I need to know how it looks before I start blending (If that makes sense!!!).
Er - I've just re-read this and it ONLY just makes sense to me, so please querie if unsure of what I'm on about.