http://www.motherearthnews.com/Sustainable-Farming/1979-01-01/More-Females-Per-Hatch.aspx Dr. N.W. Walker (D. Sc., Ph.D.) claims that you can use sorghum seeds to get ...
Some years ago, while doing research on the properties of sorghum seed, I discovered that a genetic female hormone was quite prevalent in these small, glossy kernels.
I had a feeling that this sorghum hormone could, perhaps, influence the percentage of female birds hatched, and-to check this "hunch"I set up an experiment using zebra finches ... which (because they regularly hatch up to four eggs a month) seemed the best choice available to me.
Before I began the research, these birds had hatched out a predictable half-and-half mixture of male and female finches.
I decided to keep a full dish of sorghum seeds in the aviary at all times and watch for developments.
At first the birds didn't show much interest in the new food, but-in the course of three or four weeks-they began to feed on the sorghum before moving on to their regular feeders ... and they followed this pattern both morning and evening. Then, after two or three months, I began to notice an increase In the number of female birds hatched.
In fact, by the end of the first year of sorghum-supplemented feeding, my finches produced close to four female birds for every male hatched!
Read more:
http://www.motherearthnews.com/Sustainable-Farming/1979-01-01/More-Females-Per-Hatch.aspx#ixzz1NnVj6QgV 
