When you post from Flickr, could you please use the HTML code they give? That way, we can jump straight to them even when they aren't the most recent shots on your photostream, check the EXIF data for ourselves (500mm focal length... my wife has been trying to take bird shots recently with my 70-300mm lens and will probably suggest I get one of the Sigma lenses until I tell her the price!) and meet Flickr's terms and conditions.
See the
FAQ for details.
Cheers,
Wulf
ps. beautiful shots - from a quick glimpse, I think these are some of your best bird ones yet.