For rabbits the best thing is pedialyte - like you would get for babies - I think I just read an entire Q&A on it somewhere here- I think in the behavior section. But this recipe is safe for them as well in emergenices.
For chickens I have used it lots & ducks too (and dogs & cats, and even a cow)- the product I mentioned is really good, if you can find it, buy a package to have on hand, just in case. I always do now that I know about it and have used it.The recipe I gave you, you can mix up and offer to your hen- make sure she is drinking, that is tops. Is she eating? You can also put some of it in a syringe and try and give it to her.