It's obviously my fault for living in the UK and expecting to want to enjoy my bird photography in grey January afternoons, but, I would appreciate some opinions on the following.

I took 150 shots with my 1100D and 400mm 5.6L yesterday; all of Great Crested Grebes in drab winter colours, on a drab river, reflecting the drab winter grey sky (it was sunny when I set off but turned cloudy and as usual I just hit the shutter button and hoped). The camera had centre AF point selected, and was in AI Servo mode. Every shot was very poorly focused despite the camera quickly snapping to an autofocus decision. Nothing surprising here, but my question is this......

In poor light and contrast *what* is it focussing on? Wouldn't I just expect it to hunt for focus and give up? Why a quick focus and then NOTHING in the shot in focus? I could imagine it *missing* focus and grabbing a splash of water in front or behind the bird — but \_nothing sharp*(-ish)* at all?