It's not necessary but it sure goes a long way towards a peaceful brood without anyone laying an extra egg or two in the nest if the broody has to get a drink. It also is better for her when she is first trying to keep an eye on the chicks. The other hens are naturally curious and may even peck at the little boogers and then you have a big ol' hen fight. You can move her and the eggs in the night to a new location. Don't turn on the lights, just use a dim flashlight. Put her somewhere quiet and private and she'll have a more successful time. When chickens do it out on the range, they disappear for awhile and come back leading a troop of chicks....private nest, private time with new babies. Those kinds of broods seem to be the most successful of all and also seems to yield the highest hatch rate. I normally just drape a towel over her for this transfer and upend a cardboard box with a doorway cut out over the new nest so it is dark and she doesn't feel like exploring or complaining about the new surroundings. A good broody won't leave those eggs, even without the darkness of a box, but I've had a few that really needed that extra insurance when they realized they were separate from the flock....just nerves, really. After a day, I just remove the box and see how she handles it...it always works.
