Air sac determines sex.

[NatJ]

I thought it might be affected by temperature because of chickens being related to reptiles and there seemed to be a correlation on weather until one day there wasn’t.

It has been pretty thoroughly studied, and chickens definitely have their sex determined by genes, not temperature.

All birds have sex chromosomes Z and W. A male has ZZ, a female has ZW.

Chickens, turkeys, ducks, and geese all have some color genes on the Z sex chromosome. Matings can be set up where the father has a recessive gene and the mother has the dominant gene. This gives daughters who show the recessive gene (because they inherited it from their father, and inherited a W chromosome from their mother). And sons show the dominant gene (because they inherited the recessive from their father and the dominant from their mother.)

Because the genes on the Z chromosome can be used to produce sexlinks in this way, and it does work reliably, we have pretty good evidence that sex is determined by the sex chromosomes and not by temperature.

 

[Project Blue]

Bird sex is determined by chromosomes, not temperature

That makes total sense. Alligators are weird.

 

[Largarbar]

I recently read a booklet by Thomas Quisenberry that was titled How to Tell The Sex of an Egg Before Incubation. In the book it described candling a chicken egg prior to incubation. If the air sac is off center and can only be viewed from the front and sides of the egg, a female will hatch. If the air sac is centered in the end and can be viewed from all sides, a male will hatch. This was proved in a University study. Mrs. Noda Fry was the person who reported this method to Mr. Quisenberry. She hatched 96 eggs and 92 were female. She also described holding a chick by the head. If the legs relax and hang, this is a cockerel. If the legs draw up toward the head/abdomen, this is a female.
Has anyone else ever tried this? I am about to put a couple dozen eggs in the incubator that I have candled using this method.

I love the idea of this and I hope it works for you! I saw the claim, and I am curious. Please report your findings!

 

[cassie]

I am sure it is accurate 50% of the time. If that worked, commercial hatcheries would be using it. That said, I would be happy to be proven wrong.

 

[BDutch]

Old thread. But interesting if anyone has proof something like this works

In western Europe some large hatcheries use a method with puncturing eggs. The machine adds a little egg-white in a tube filled with a liquid, that changes colour soon after. The hatcheries use this method with 8-9 day old developed eggs. This way they don’t need to kill male chicks.