I had seven responses to this problem. Most noted that the images were inaccurate, childish or stylised. There was no support for my proposal that the right bird of the left stamp was a Tengmalm's, with the most popular suggestion that it is actually Tawny (grey morph). The left bird on this stamp was generally accepted as Tawny with incorrect eyes.
The right stamp caused a few more problems. For the perched bird, opinion was almost equally divided between Eagle Owl and Long-eared Owl. If the birds on the stamps are to scale, then the latter is more likely, but there are features which suggest the former. There was strong support for the flying bird being a Little Owl, though some considered it to be a second Eagle Owl.
I will settle for my original suggestions except for the Tengmalm's.
Added 5th October 1999