I’ve done that successfully with newly hatched chicks, given a hen chicks that I hatched in an incubator and put under her when she did not already have chicks. The hen had been broody for over three weeks, much like yours. Several times I’ve successfully given freshly hatched chicks to hens that already had chicks the same age, but that’s not your situation. I also partially failed once when I added chicks to a brood the hen already had but that’s a different story. That failure was due to imprinting.
I take the chicks to the coop after dark and put them with the hen, while removing any eggs under her. I turn the lights on in the coop so I could see what I was doing, I don’t want to injure a chick by mishandling it or crushing one while I’m inserting another. I do not force the chicks under the hen, just put them in the nest with her. They soon go underneath her.
Some broody hens will mother about anything, others not so much. This process works best when the chicks are very young, the younger the better. Straight from the post office or straight from the incubator is best though sometimes it works when the chicks are older. When dealing with living animals you can’t predict what will actually happen.
The chicks and the hen imprint on each other. It’s not just a question of will the hen accept the chicks, it’s also will the chicks accept the hen. This works best when the chicks are very young. Sometimes when a chick disobeys the hen she pecks them to discipline them. She’s not trying to kill them, she’s trying to teach them that they need to obey her. This can happen with chicks she hatches herself but is much more likely with older chicks.
Three different things might be going on when a hen pecks a chick, I’ve seen them all. She might be disciplining it, no big deal. It’s part of being a parent. She might be trying to drive it away if she doesn’t accept it. She’s not trying to kill it just drive it away, sometimes accepting some chicks but not others. The chicks don’t want to leave so they can be injured. Or she might be trying to kill it. It’s not always easy to tell exactly what is going on. An occasional peck is fairly normal but repeated pecks are generally bad news.
When the hen wakes up the nest morning with a bunch or chicks under her, she usually accepts them. Not always but usually. When I do this it’s always with chicks straight out of the incubator. The chicks absorb the yolk when they hatch and can go several days without eating and drinking. When they start getting hungry or thirsty they tell the hen with a special “distress” peep. That’s when she knows she needs to take them off the nest to find them something to eat and drink. One time I had a hatch where a few chicks started hatching on a Monday but the hatch did not finish until Wednesday, so I put the chicks under her Wednesday night. The hen did not bring those chicks off the nest until Friday. They were fine. I’ve had hens bring their chicks off the nest the next day, long before the chicks were close to getting hungry or thirsty. You just can’t tell what a living animal will do.
Other people use other methods. Some put the chicks near the hen during the day and see how she reacts. I’ve done that with a hen that already had chicks. She called the new ones over immediately. There are always a lot of different methods to do these things.
Cochin are known to be good mothers and your hen has been broody over a month. If your chicks are very young I think your chances of success are pretty good, I’d certainly try it. But the older they get the less likely you are to succeed. If you try the overnight method, be down there early the next morning so you can see what is going on.
