From the exif data, it looks like a 300mm f/4 with a 1.4 TC. Very nice, Rob (and everyone—I love the photo-a-day thread). A long time ago this forum seemed be dominated by birders. What happened?
Right on the money jonny, D3100, AF-S 300mm F4 w/TC14E. I normally use a D300, but the D3100 has better high ISO performance, so when I know the lighting is going to be bad I take the D3100. I bought it as a hold over till I decide whether I'm going to go FX or not.
As for birders, well it is an expensive arm of photography, and no overly exciting gear that would be relevant to birders has come from Nikon lately, so that might be why you don't see many here now.