We have a 15-month old Silkie hen (Marsha--short for Marshmallow Fluff) that was given to us in July. Since then, she has gone broody at the beginning of August, beginning of September, and is once more broody (it's the beginning of October). The other two times we broke her using the broody box--an old wire dog crate with hardware cloth across the bottom, elevated off the ground to let air flow freely (in the warmer months we even had a fan blowing across the bottom). When we let her out, she runs to go eat and scratch with the other hens, is healthy and active and talkative, but within 15-20 minutes, she freaks out and makes a run for "her" nesting box. ("Omigosh! My imaginary eggs! I've got to get back to them!")
The first time it took only about 4 days for her to snap out of it. September's broody spell took nearly a week to break. September 29th rolled along and she was again in a nesting box all day/night long. We put her in the broody box on 10/1. Then yesterday (10/3) she laid an egg in the broody box, which shocked the tar out of me: we didn't think broody hens laid eggs. However, that's the only explanation, unless one of our pullets snuck in there when we let Marsha out for a bit of a scratch, laid their first egg, and snuck back out without a peep.
We're loathe to keep Marsha in there a week out of every month (since she seems to go broody like clockwork), especially with the weather turning much colder and Silkies not being able to keep warm as well as the other chickens do. So we decided that, since she's not a great egg layer to begin with, we'd just let her stay in the nesting box (we have 4 other boxes available and only 1 other laying hen at this point). I mean, why stress the poor bird out? However, I read this morning that it's not healthy to let a hen stay broody if she's not actually hatching eggs, that it takes too much of a toll on her physically.
We considered getting her some eggs to hatch, but we already have 12 chickens in our flock and a smallish coop--we really don't need or want more at this point. Then I considered letting Marsha hatch eggs for other flock-keepers who didn't have a reliably broody hen, but I was told that that's not really safe--there could be health issues with eggs brought in from other local flocks--and winter's also just a month or so away. That's probably _not_ the best time to be raising chicks
My next plan is to try the ice packs underneath her, but I'm afraid she'll just move to another nesting box. Once they've chosen a box to brood in, will hens willingly move?
Are there any other suggestions for keeping Little Miss Broody-Britches from living in a nesting box all winter? (other than the "dunk your hen in ice water" idea--I refuse to try that). This is our first flock, so we're still very much on a learning curve
(And there are so many broody hen threads that I wasn't sure where to post this, but this looked like a good spot. If I need to move my post let me know, please--this is my first time participating here

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Our Flock
The Hens:
Marshmallow Fluff (white Silkie)
Feta (white bantam Cochin)
The Younglings (born 6/16/14):
Yekatarina, Raisa, Tatiana, Natalia (Red Stars)
Anne, Elizabeth, Mary, Victoria (Speckled Sussex)
Pepper (Silver-laced standard Cochin)
Ginger (Partridge standard Cochin)