These tiny beautiful bird feed on grass seeds,they are only around 3 inches long,and difficult to photograph.A small party of them were outside the observatory yesterday and some hoped up on to a fence post,I managed a few quick photos with my 50D and 400 L lens,distance was 4.2 metres,both images cropped.
Great job. They're rather difficult to sneak up on, aren't they? I was going to ask which 400L (2.8 IS, 4.0 DO, 5.6, et al) but then I saw it in your signature