Help needed, birding with a D5000.

Thanks for your reply, I know what you mean about the focus point as I often have to move it back but I usually notice when its gone walkabout,

I am fairly new to DSLRs but I usually use spot focus & aim for the eye?

I have taken hundreds of birds photos in the last few weeks & would guess around 10% are keepers with a touch of sharpening,

I am amazed how good the Sigma lens is for the price but just wondered if there was any way to upgrade to a sharper lens within a £300 budget.

(I have included a couple of my bird shots I am fairly happy with which have had minor tweaking in pp)

Nuthatch cropped & sharpened.

Great Tit cropped & sharpened.