Toxicity of Marijuana to Poultry
I would imagine finding such information would be difficult due to lack of studies having been done. That being said, for all the tales of the damage that marijuana grows do to the environment when they are done in hidden areas of wildland, etc the one thing you never hear cited as a hazard is harm to wildlife from consuming the plants themselves (you do hear about the water being impacted by heavy runoff of chemicals for these grows, but they are different than what you would have for personal use).
That being said, given the potential damage to the plants I would think the best approach would be to configure your grow so that it is separate from the area in which the flock is able to access....this would have the added benefit of eliminating any potential danger to the birds.
This site may be of help to you - this article is more about the more commonly accepted hemp products, but the site itself seems a good resource: http://www.leafscience.com/2013/10/24/chickens-hemp-diet-lay-healthy-omega-3-eggs/
I'm in Oregon and it seems everyone is growing it here. The chickens will pick at it, and if there isn't much green around them they will completely destroy them. If you want to grow it for human use you will need to protect it. I don't grow it myself, but I can say my chickens pretty much eat everything and if they don't eat it, they kick it to death. ;)