How to Sex a Chick

i-75fa6f7cebb4145668724f37f5a52b36-steve_icon_medium.jpgResearchBlogging.orgSexing chicks is a very difficult task for naive people. Expert chick sexers are over 98% successful while the naive sexers can only do it with slightly above chance performance. Are you sufficiently confused/pissed yet?

Ok ok... here's what's really going on:

When chickens are born the chicks are examined by experts to determine what sex they are. This important task is performed in order to save money in feed costs and avoid conflict between the male and female chicks (the men are selfish and don't let the females eat or drink). What they do with the male chickens I'm not entirely sure. I would assume they euthanize them.

In any case, this process was discovered by the Japanese and brought to America in the 1920's where a number of chicken sexing schools were setup in Washington and California. According to the industry the skill requires years of practice to master. In fact, the experts are able to classify nearly 1000 chicks per hour with 98% accuracy. The process of sexing the chicken is both interesting and disturbing,

The chicks, only a few hours old, are brought to the sexer in trays of 100. The task requires that the cloaca be everted. The chick is held in the left hand (for a right-handed person) and the fecal contents are squirted into a container to clear the cloaca (see Figure 2). Gentle but firm pressure from the two thumbs and right forefinger are exerted to spread the ventral surface of the colaca upwards to expose the eminence, called the "bead." The eminence is about the size of a pin head. The sexing decision must be made quickly because the chick is at risk from the vent eversion. Females are traditionally place in a tray on the right and males on the left.

Here is an example of how an expert would hold a chick in order to sex it. The chicks eyes have been obscured in order to maintain privacy.


It's pretty amazing what you can sneak into a psychology journal article isn't it?!

ok ok ... Back to the chicken sexing...
Here's what the chicken sex organs look like:


Can you figure out what makes one female and one male? I sure can't and neither could a number of experts in visual cognition or any of the subjects in a study by Irving Biederman and Margaret Shiffrar published in the Journal of Experimental Psychology: Learning, Memory, and Cognition (1987, 13(4), 640-645).

In short, Biederman and Shiffrar discovered that they were able to train novice experiment participants to perform as well as the expert chicken sexers by giving them a short training session that instructed them as to where the non-accidental contrast in shape of chicken organs (concavity vs. convexity) was.

Here's their conclusions:

A contrast in a nonaccidental property can be readily learned and used as the criterion for rapid and accurate classification of complex objects. It is, of course, possible that such contrasts might not be available, in which case classification would have to be accomplished by prototype (or multiple-cue) matching. We suspect that nonaccidental contrasts will be spontaneously used whenever they are obvious. When not obvious because of small size, variability, or embedding in a complex object such as a chick cloaca or tank, a good instructional program is well advised to specify the contrasts rather than hope for their discovery.

Check out this Dirty Jobs segment on this exact topic. Ewww!

Report on:
Biederman, I., Shiffrar, M.M. (1987). Sexing Day-Old Chicks: A Case Study and Expert Systems Analysis of a Difficult Perceptual-Learning Task. Journal of Experimental Psychology: Learning, Memory, and Cogntion, 13(4), 640-645.

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Sexing a chick sounds pretty easy. But only say this because my sister used to sex fruit flies which she says pretty challenging and hard on the eyes. She had to separate males and females for her genetics experiments.

Reminds me of an old "Dennis the Menace" cartoon.
Dennis and his little friend Alice have some kittens and Dennis is holding one upside down and says to Alice, "Well, my dad can tell by looking at the bottom of their feet."

Bibliophile: I'm not sure where that comes from. In NZ, they put the males in one half of the shed and females in the other half. Males grow faster, so there's no point in euthanising them...

Jiminy... JG- I also had to sex fruit flies for my genetics classes- and I'll be whipped if chickens aren't more difficult to do.

Drosophila melanogaster: the males have a tiny but visible set of black "sex combs" on their rear legs. Easy to see if you know what to look for.

Chickens: some bulbous flesh vs. other bulbous flesh. I'd suck at separating the two.

So not the advice I was looking for...:(

By Disappointed (not verified) on 15 Apr 2008 #permalink

I should also point out that the contemporary technique relates to the wing feathers somehow. My father could tell you more, he was learning it before we sold the chicken farm

We used to buy all-male chicks, which we picked up at the post office. We would raise them to be fryers. Would get enough mis-sexed females to have enough around for eggs. You realize what the chick sexer is looking for is the male's penis, which disappears very shortly after hatching.

By Jim Thomerson (not verified) on 16 Apr 2008 #permalink

my, my, my...

i just found your post and found it very curious.
i've been involved in the poultry for >30 years and am currently a prof of poultry genetics at 'dear old state'.

sexing chicks by vent-sexing is extremely difficult, and certainly doesn't compare to fruit flies. and your figure of 98% accuracy is woefully low. in a poultry house of 100,000 chickens ... you'd still have 2,000 of the wrong sex!

there was a 'sexor' i worked with in harrisonburg,va way back in the 70's -- who graduate #1 in his class. the 'final exam' was to sex 10,000 chicks. he got 1 wrong, and his best friend (at the time) got 2 incorrect -- the 'best' friend was so angry, they never spoke again.

if you are really interested, you might try here for a brief description of how contemporary chicks are 'sexed' using sex-linked genes.

for a more hi-tech approach, how about this???

Looks like someone got angry that you misled them with the title so they decided to spam you.

By Feynmaniac (not verified) on 11 Nov 2008 #permalink