Why does my hen throw grass on her back?

[jaxneptune]

Almost all of my hens will show broodiness every once in awhile. One does it every month or two. When I take her out out to let her range with the rest of the flock she just lays on the ground all fluffed up. Then she proceeds to pull up grass and throw it on her back. I usually isolate her for a couple of days and she returns to normal.

 

[Pinky]

I've heard that some hens will do that to collect materials for their nests.

 

[Boo-Boo's Mama]

All of mine do it every day. Seems to be an indication that they got the deed done, even when they didn't!