The stamps feature the Tjif-tjaf (Chiff-chaff) and the Groene Specht (Green Woodpecker).
You can get a better view with this image. The stamps can be scanned using an app to hear the sound each bird makes.
This amazing piece of mail art was a bit harder to document than normal...after carefully removing the outer wrapper, there was a baguette bag...
And inside was a very long continuous piece showing beautiful drawings from Heleen of all the birds I mentioned I liked a while ago. Plus some other birds collaged on.
This was a big 'WOW'. Thank you, Heleen!