Gender Ratio of As-Hatched Chicks

You would think chicken eggs should hatch 50% pullets (females) and 50% cockerels (males). Anyone who has hatched or bought chicks knows that the gender ratio of as-hatched chicks, otherwise known as straight-run, is rarely 50/50.

One year I hatched four dozen Silkie eggs, the vast majority of which turned out to be cockerels. The next year I again hatched four dozen Silkie eggs, almost all of which were pullets.

This year I purchased 17 straight run New Hampshire chicks, and all but one are cockerels (94%). At the same time, I hatched 8 Ameraucana chicks, and all 8 (100%) are pullets.

The gender ratio of as-hatched, or straight run, chicks has been compared to tossing a coin. In both cases, each individual incident (hatch or toss) has two basic choices — male/female or heads/tails — leading to the 50/50 assumption. As bad luck would have it, in both cases this assumption is false.

In an unscientific experiment, I asked my husband to toss a coin while I recorded the results. At 5 tosses, tails came up 80% of the time. Ten tosses resulted in 70% tails. At 20 tosses, the results were 55% tails.

For a more mathematically accurate assessment of coin toss probability, I consulted an online coin toss simulator. The results showed that our coin toss results were not that far off. At 5 tosses, the simulator showed 80% tails; at 10 tosses, 60% were tails; at 20 tosses, the results were 50/50.

These statistics square with something Jeff Smith of Cackle Hatchery once mentioned to me: The 50/50 average rarely kicks in for 20 or fewer straight run chicks. The smaller the number of chicks, the more likely the gender ratio will be terribly skewed one way or the other.