Over the years - with the large family of Old English (aka Jungle Fowl) living semi-wild on and around my property - have seen about every variation possible with Hens and Baby Chicks.
One interesting example:
A group of 3 sisters - couple of them laid eggs in same nest, one sets for the 21 days, right after hatching another takes and raises the babies, while 3rd plays additional surrogate mom.
But, here's one for the record books, forget a Hen adopting Babies ...
Had a Rooster do it.
After a mom with a group of 2 day old babies was killed by a hawk, I managed to corral those babies into the pen where Stubby the One Legged Rooster lived (Stubby is another story unto himself), and following a few minutes of curiosity, he allowed them to nest under him at night and he 'mother hen' raised them during the day (and rooster taking interest in helping a mom to feed babies is fairly common, somewhat similar to how a rooster entices a hen offering her food)
After a few weeks, about the time the orphans were getting too big for Stubby to easily manage - was another hen with a new clutch of her own who then took over from Stubby, and raised both groups.
Amazing isn't it ?
Seems so often all we have to do is stand clear - and Mother Nature has a way to work things out just fine almost every time.
Now, got pictures of Stubby with those babies, and - if it's ok to 'advertise' for these folks - sent the pics to Chicken Rescue group in Minnesota, who selected one to feature in their 2009 calendar.
You can go there to see those pictures, Google for "Chicken Run Rescue" (maybe buy a calendar too)
And, now that I've opened my mouth on all this - will also post on my website in next few days -
http://bckelly.com/chickens
Thanks
BC Kelly
Tallahassee Fla