Air sac determines sex.

[horselover1999]

I greatly appreciate the insight, especially considering your background and experience. About the only way I know to sex chicks with any accuracy is the wing feather method while they are still fluff balls.

Frostranger is correct, they need to be specifically bred for feather sexing to be feather sexed. Even if they are bred for it, they do need to be (I think) at least 6-12 hours old to be accurate, just for some feathers to have time to grow in.
Vent sexing is common, but takes some practice and skill to not hurt the chick. I think there are some videos on Youtube, but I haven't tried it.
I can wait the 3 weeks it takes for secondary sex characteristics to show up.

Some breeds are able to be auto-sexed at hatch, like the barred Plymouth Rock, Bielefelder, Legbar, and Welsummer.

 

[MysteryChicken]

Feather sexing can only be done on certain crosses. If the chick doesn't have the right genetics it won't work

It works for me, but I use a different technique. I sexed Someone's Silkie chicks 100% accurately a few years back by my method. They had them DNA sexed afterwards to confirm it. It was a member here on BYC, but don't remember their Username.
I call it the Butterfly Method.

 

[Kiki]

It works for me, but I use a different technique. I sexed Someone's Silkie chicks 100% accurately a few years back by my method. They had them DNA sexed afterwards to confirm it. It was a member here on BYC, but don't remember their Username.
I call it the Butterfly Method.

What is the butterfly method?

 

[MysteryChicken]

What is the butterfly method?

It's a different form of wing feather sexing I came up with years back with new batch of chicks.
I use wing shape, & or gap for sex determination. There's a small margin of error like all the other methods though. Bound to get some wrong on occasion.

Female at 1 week. Butterfly shape no gap. (Primaries longer then Secondaries)

Male 1 week. Butterfly, with Gap. (Primaries Even with Secondaries.)

 

[MysteryChicken]

One more example.

Male 1 week. Butterfly Shape with Gap.(Primaries Even with Secondaries)

Female 1 Week. Butterfly Shape, no gap. (Primaries longer then Secondaries.)

 

[Slothinc]

One more example.

Male 1 week. Butterfly Shape with Gap.(Primaries Even with Secondaries)View attachment 4047490Female 1 Week. Butterfly Shape, no gap. (Primaries longer then Secondaries.)View attachment 4047491

Wow this is so cool!! Thanks for sharing! Does it need to be done right at one week? lol I wish I had known about it several weeks ago, I would have tried it with all of my grow outs and been able to see if I could do it accurately!!

 

[007Sean]

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 call it

Too small of a sample size used in the study. Plus, other obvious inaccuracies.

 

[MysteryChicken]

Wow this is so cool!! Thanks for sharing! Does it need to be done right at one week? lol I wish I had known about it several weeks ago, I would have tried it with all of my grow outs and been able to see if I could do it accurately!!

It can be done as early as 1-3 days, but everything is more clear at 1 week.

 

[NatJ]

I just read the abstract and part of the intro and I can already poke a couple holes into their study. You should not be able to poke holes into a correctly done peer-reviewed publication.
1) The second sentence mentions ethicality, which depends on the person and is not a fact. There are several ways to humanely and effectively euthanize chicks.
2) They might say it is 80% effective, so just don't incubate the "male" eggs, "saving 5.65 billion chicks from being slaughtered." That is ignoring the approximately 20% of female chicks in the "male" eggs, and the approximately 20% of male chicks in the "female" eggs. They don't look at the amount of chicks that makes up this combined 40%, so almost half, about the normal male:female ratio.
3) The authors are in electrical engineering, and didn't bring in a co-author that is in a relevant department?
I didn't want to read the rest of it, I don't trust their accuracy.

Egg shape is determined by the shape of the hen's uterus/shell gland, and might change over time, but very, very, gradually over her productive life.
Hens do determine the sex of the chick with ZW, while rooster have ZZ chromosomes, but that affects the embryo, not the shape of the egg.
While I was at my internship with Tyson's genetics supplier, Cobb-Vantress, they were talking about a new method to determine sex in ovo by shining a laser into/through the egg and reading the wavelengths it produced. I haven't looked into it, though, and I think it would be too expensive for the average person to get if it was proved accurate. It also might have to be done before the egg is incubated, and require the shell to be opened a bit, increasing the chance of bacterial contamination and decreasing hatch rate.

Holding chicks by the head to see their reaction is inaccurate. Their reaction really depends on the bird's personality.

Signed
-Bachelors of Science, Poultry Science
-Masters of Science, Animal Science (Poultry)

The conclusion of the study mentions one of the other points that I see as a big problem, the small sample size:
"In this study, a total of 60 used eggs, and only 47 of them were hatched. This number is comparatively low, and a large number of data is needed for better results."

And I also see a problem with them training the computer on those 47 chicks, then having it predict the sex of those SAME chicks to check the accuracy. So even with all the right answers, the computer had a pretty low accuracy (better than random chance, worse than the usual after-hatch sexing methods.)
"37 out of 47 (0.787) chicks were classified correctly."

(Quotes are from the previously linked study:
https://pmc.ncbi.nlm.nih.gov/articles/PMC9832119/)

I'd like to see further research on the matter, to prove out whether it really does or does not work. My bet is that it won't work, but proving it one way or the other would be better than forever wondering. I don't personally care enough to do controlled experiments.

Edit to clarify: this is the study in 2023 that someone linked, not the one mentioned in the first post of the thread.

 

[tlcmurphy]

One of the hallmarks in research is whether your data can be repeated by another investigator. If not, I also call BS.
Additionally the original research appears in a low Impact Factor journal.

(Research scientist in another field).