These feathers are knitted and woven at the same time with special weave-knit needles from Addi.
See this video.

I want to make some more of these feathers to use in the big bird I want to make for my art project about bullying (see my website feathers and dragons)

I have made some more feathers now and used the long and crossed stitch in them. It works well. You get more a lace effect. The long and crossed stitch I have described here. I have outlined these feathers with crochet.

Decided to do the same kind of outlining with crochet (sc and picots) with the other ones.