I found this great post at fresheggsdaily and had to pass it on. By the way fresheggsdaily is a great resource for people with chickens or thinking about getting chickens. The information is interesting and proven to a degree. The way you do it is by temperature control. I have seen this on nature shows when it comes to crocodiles. If their nests are a certain temperature more males than females will hatch. I am definitely trying this out! Click on the pic below to go to the post. Also check out some of the incubators available from my amazon affiliate partner. If you buy one I get a small commission that goes to support this blog. Enjoy!