We often fall victims to popular cliches when it comes to lens purpose "compartmentilizing". Thus, all of us head to the duck pond with that 300, 400 or 500 mm lens. However, it is often more profitable to use a shorter FL and compensate by ingenuity of approach and proximity.
As an example, I think Gary Fairhead's bird shots with his old 200 mm are at least as good as the ones he gets with the 400 mm these days.
I personally think my best birding lenses are 135L and 200 f/2.8, especially when it comes to in-flight shots. The 300 f/4 IS is pretty capable too.
Sorry for pontificating, could not help it.
I did find the 15mm swan shot. I wish I had my rubber boots on....then I would have gotten him good.
HOSTED PHOTO
please log in to view hosted photos in full size.