Sexing 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!
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.