Urmas, The feather was already there. Maili has lifted it with a bundle of nesting material. The feather was on the right side. you can see it in the video.
13:51 she grabbed the feather from the nest edge
16:04 the feather was on the front - close to the birch branch
16:05 a wind gust has blown it in the nest
16:05:26 there was another gust of wind and the feather landed in the middle of the nest