“Unlocking the Secrets of Chick Sexing: The Surprising Science Behind This Hidden Goldmine”

What is the strangest job you have ever had? Snake milker? Professional cuddler? Dog food taster? Online educational content creator? Professional queuer (and yes, these are all very real)? Well, if you have a taste for offbeat employment, why not consider a career in chick sexing? No, not having spicy time with our delicious avian drumsticks, but the fine art of determining whether a chicken is male or female shortly after it hatches. Described as the poultry industry’s “secret weapon”, this occupation saves factory farms millions of dollars every year and is key to keeping our grocery store shelves well-stocked with chicken and eggs. It is also a highly specialized and surprisingly difficult skill to learn, with experienced practitioners developing an almost supernatural ability to spot the almost imperceptible differences between male and female chicks. As a result, the occupation of chick sexer has historically been highly sought-after and lucrative, and even helped an entire generation of immigrants survive and thrive in an extremely hostile period of American history. This is the forgotten and surprisingly inspirational story of one of the world’s strangest occupations.

For much of human history, poultry husbandry was a fairly straightforward process. Once hens laid their eggs, some were collected to be eaten while the rest were allowed to hatch. On average, around half these eggs would hatch into males or cockerels and half into females or pullets. Both were allowed to grow and mature naturally, whereupon the mature hens would either be slaughtered for meat or retained for egg production. Meanwhile, a handful of mature roosters would be retained to breed with the hens, while the rest were slaughtered for meat. And once a hen’s egg production started to drop, she too would often follow her male brethren and period nuggets to the kitchen table.

But all this began to change in the early 20th century as farming became increasingly industrialized and certain hens – aka broilers – were selectively bred to produce more and more meat. Suddenly, roosters became much more of a liability. Not only did they now no longer produce enough meat to be economical, but roosters are also highly ornery, prone to starting fights and injuring or even killing other roosters and hens. But eliminating these unwanted roosters posed a vexing problem. Chickens don’t have penises, meaning it was nearly impossible to tell hens apart from roosters until they started developing their secondary sex characteristics – for example, the rooster’s distinctive comb and wattles. These indicators, in turn, don’t appear until five to six weeks after hatching; meanwhile, the largely useless cockerels continue to take up space and consume feed, costing the poultry industry millions every year.

Because humans are stupid, traditionally, chicken farmers used a variety of folk methods to predict whether an egg would hatch into a pullet or a cockerel. For example, a ring suspended by a thread over an egg was said to swing one way for a male and the other for a female, while the shape of the egg itself purportedly indicated the sex of the chick inside. In reality, egg shape is linked to breed or even individual hens, meaning these methods are no more accurate than chance. A better method was needed if the industry was to expand further and become more efficient.

The first attempt at a solution was devised in the early 1920s by Cambridge University geneticist Reginald Punnett – whose name you may recognize if you ever had to construct Punnett Squares in high school biology class. Punnett developed the world’s first autosexing chicken breed, the Cambar, whose cockerels and pullets had different colour patterns and could be easily distinguished immediately after hatching. While this was a significant development, unfortunately the Cambar and subsequent auto sexing breeds like the Gold, Silver, and Cream Legbars were not particularly good meat or egg producers compared to conventional chicken breeds. It was assumed that these traits would eventually be bred into these lines, but this research was interrupted by the development of another, more efficient sexing method on the other side of the world.

In 1925, Dr. Kiyoshi Masui at Tokyo Imperial University discovered a reliable method for determining the sex of ordinary chicken breeds within a day of hatching. This involved opening up and peering inside a chick’s vent or cloaca [“Klo-ay-ka”] – an orifice found in all birds, reptiles, and amphibians; some fish; and a handful of mammals which contains the openings to the digestive, urinary, and reproductive tracts. The cloacas of male chicks typically feature a pimple-like protuberance or “eminence” on their lower rim – a rudimentary sex organ – while those of female chicks do not. Simple, right? Well, not quite, as indicated by the very important word typically in the previous sentence. For you see, around 20% of male chicks possess no easily recognizable sex organs, while 40% of female chicks possess protuberances and other cloacal structures very similar to their male counterparts. However, Dr. Masui managed to catalogue and categorize the dozens of subtle differences and cues that could be used to tell even these fringe cases apart. For example, female protuberances tend to have a dimpled surface or a more pearlescent sheen, and will temporarily disappear when rubbed with a finger. In 1933, Masui and colleague Juro Hashimoto published their findings in a landmark 1933 paper titled The Rudimentary Copulatory Organs of the Male Domestic Fowl and the Difference of the Sexes of Chickens.

At first, it was believed that differences outlined in Masui and Hashimoto’s paper were far too subtle to be of practical use to the poultry industry; it would simply take too long to examine each chick and accurately tell them apart. However, Japanese poultry workers soon succeeded in developing a practical and fast method of cloacal or vent sexing, and founded the Zen-Nippon Chick Sexing School to teach it. This method, which takes two or more years of intensive study to master, requires nearly zen-like concentration and the manual dexterity of a surgeon. To sex a chick, a trained sexer picks up a chick, flips it over, and applies gentle pressure to the abdomen to expel faeces from the rectum. The amount of pressure applied must be carefully calibrated, for too much can easily injure or even kill the chick. Once the digestive tract is cleared, the sexer pries open the cloaca with their thumb and peers inside to determine the sex of the chick. At first, trainees can only sex a chick a little over 50% of the time, but with continuous practice monitored by an experience mentor, their speed and accuracy steadily improves until they are able to sort 800-1400 chicks per hour with an accuracy of 98%. Many graduates have achieved even more impressive feats, with the fastest recorded sexer sorting a phenomenal 10,000 chicks in a single eight-hour shift. In a typical 100-day hatching season, a single chicken sexer might handle at least 300,000 chicks.

This accuracy is doubly impressive considering just how little time sexers spend looking at each chick – on average less than three seconds. In that short span of time, the sexer must consider dozens of tiny, extremely subtle clues in order to tell apart the edge cases that don’t conform to the eminence/no eminence rule. It is a skill which takes years of dedicated practice to acquire and one that strangely seems to transcend conscious analysis. Indeed, when asked, many chick sexers are unable to explain just how they go about making their selections – they just immediately know whether a chick is male or female. As cognitive scientist Richard Horsey writes in his article The Art of Chicken Sexing:

“To be close to 100 per cent accurate at 800 to 1200 chickens per hour for a long day, intuition comes in to play in many of your decisions, even if you are not consciously aware of it. As one of my former colleagues said tome…‘There was nothing there but I knew it was a cockerel’. This was intuition at work.”

So intensive and all-absorbing is this work that, as R.D. Martin, author of the book Specialist Chick Sexer writes:

“If I went for more than four days without chick sexing work I started to have ‘withdrawal symptoms’. Several of my students have expressed the same  feeling when they have not sexed chickens for a week or so.”

But, I mean, who hasn’t been there? …

The intuitive and automatic nature of chick sexing has attracted the attention of many psychologists, who have tried to work out exactly how the brains of chicken sexers so quickly process the subtle clues that they perceive. In his article, Richard Horsey draws a parallel between chick sexers and Second World War pilots, air gunners, and ground observers, who were trained to rapidly identify aircraft – and distinguish friend from foe – at a distance. Though trained to systematically analyze aircraft by the shape of their wings, engines, fuselage, and tail – what was known as the WEFT system – with sufficient practice these spotters became able to instantly, and automatically identify aircraft by their overall “feel.” A similar concept exists among bird watchers, as Horsey explains:

“Experienced bird-watchers develop similar skills. After a great deal of practice, many bird-watchers can identify a bird by the ‘way it looks’, even when the bird is glimpsed too briefly, or is too far away, to allow individual features to be identified. They even have a name for this brute property, which they call the bird’s ‘jizz’. This skill takes some time and effort to develop, and is similar to chicken sexing in that birdwatchers perceive the jizz as a gestalt, but cannot say what the features are that make up the whole.”

Some psychologists have argued that aircraft spotters, bird watchers, and chick sexers perceive their targets as a unified whole or gestalt, and do not engage in conscious serial processing. Indeed, this has been suggested as one possible model for how we learn to read written language. As Horsey explains:

“For accomplished readers, however, the process [of reading] is fast, accurate, and subconscious— that is, we are not aware while reading of the actual process involved in converting the visual stimuli into meanings. In fact, most people have the impression that they recognise whole words at a glance, rather than having to sound them out. It is this impression that forms the basis for the ‘whole-word’ approach to the teaching of reading. On this approach, children learn by rote how to recognise at a glance a basic vocabulary of words. They then gradually acquire new words through seeing them used in the context of a story. This is in contrast to phonics, the other main approach to reading instruction, which explicitly teaches the connections between letters and phonemes.”

Experimental research, however, suggests that this premise is actually false:

“In a series of experiments, Van Orden (1987) and Van Orden et al. (1988) began by asking subjects a question, such as ‘Is it a flower?’. The subject was then presented visually with a word (e.g. ‘rose’) and had to indicate whether the word fit the category. Sometimes, subjects were offered a homophone (either a word or a non-word), such as ‘rows’. Subjects often mistakenly identified such words as fitting the category, providing evidence that readers routinely convert strings of letters to phonological representations, which they then use to access semantic information for the lexical item.”

Indeed, studies have shown that when a bird watcher, aircraft spotter, or chick sexer is given a new piece of information for distinguishing between different targets – for example, that two very similar birds can be told apart by a wing stripe – this will improve their supposedly automatic, intuitive abilities in the long run despite them being consciously aware of the information. Instead, Horsey suggests that such ‘intuitive’ classifiers do in fact engage in serial processing, with the extreme speed of their analyses stemming from the specific order and method by which perceived clues are processed:

“I would like to focus on one rather novel explanation for our object categorization capabilities, put forward by Berretty et al. 1999 within Gerd Gigerenzer’s ‘fast and frugal heuristics’ framework [which] postulates simple rules that allow us to make accurate decisions under time pressure. [For example], consider the hiker who comes across a bird while walking in the alps. In trying to identify the bird, the hiker takes out their bird book and uses a number of features of the bird (cues) to correctly identify it. Second, we are asked to consider the rabbit, who has a far more limited aim when it sees a bird: identify it as predator or non-predator, as quickly as possible.

The basic point is that since its survival is at stake, the rabbit does not have the luxury of adopting a strategy of the kind used by the hiker—considering a relatively large number of cues, some possibly redundant, to come to an accurate identification. In particular, the rabbit needs to come to a decision on whether the bird is a predator as quickly as possible, and will therefore want to use the smallest possible number of cues. It will also want to stop the identification process as soon as a decision can be reached, rather than making use of all available cues.

Berretty et al. suggest a categorization procedure which they term ‘categorization by elimination’. Cues are accessed sequentially in a pre-determined order, and each cue eliminates candidates from the set of possible categories for an object (initially, this is the set of all categories). When only one category remains, the procedure stops, and the object is assigned to this category. In the case where all cues are exhausted, and more than one possible category remains, a random assignment is made.”

The psychology of this kind of high-speed mental analysis is being closely studied, as it may have useful applications in the interpretation of complex data such as earthquake seismograms, mammograms and other medical imaging, and even wine tasting – and for more on how seismic data is currently analyzed, please check out our previous video What is Up With the Bizarre Richter Scale?

Whatever the psychological nature of their remarkable abilities, graduates of the Zen-Nippon Chick Sexing School quickly revolutionized the Japanese poultry industry, allowing hatcheries and farms to become far more efficient and productive by eliminating the need to house and feed useless cockerels. Indeed, official records indicate that by 1932, Japan was producing 12 million more head of poultry than it had in 1932, while the average egg production per hen increased from 107.2 to 122.8. Worldwide, vent-sexing is believed to have reduced the cost of raising chickens by as much as 50%.

Unsurprisingly, word of the miraculous Japanese vent-sexing method quickly spread, and soon the Zen-Nippon School was sending consultants all around the world to teach others the technique. For example, in 1933 Hikosaburo Yogi visited the United States to demonstrate the technique, achieving phenomenal accuracy rates approaching 100. The following year Dr. Kiyoshi Oxawa introduced vent-sexing to Australia, while the year after that Kiochi Andoh introduced it to England. And in 1937 Shigeru Nitta founded the American Chick Sexing Association or Amchick, which had branch offices in Lansdale, Pennsylvania, and Nokomis, Illinois.

However, few foreign sexers ever attained the extreme proficiency of the Zen-Nippon School graduates, meaning Japanese chick sexers remained in high demand. This extreme specialization and demand proved especially advantageous to Issei, Nisei, and Sansei – first, second, and third-generation Japanese immigrants to the United States – who faced widespread bigotry and discriminatory legislation like the Alien Land Laws, which prevented foreigners ineligible for citizenship from owning or leasing land in several states including Arizona, Arkansas, California, Florida, Idaho, Louisiana, Minnesota, Montana, Nebraska, New Mexico, Oregon, Texas, Utah, Washington, and Wyoming. By leveraging their cultural connections to Japan and hiring from within their own community, Japanese chick-sexing associations managed to nearly monopolize the American poultry market, allowing their members to secure stable, extremely high-paid work in spite of societal prejudices.. Indeed, even novice sexers could pull in a respectable $6-7 an hour, while expert hands could make nearly $3,000 in a 100-day hatching season – an enormous amount in the mid-20th Century. Even today, chicken sexers can start at $60,000 a year – double the salary of most other hatchery workers. As Roy Akune, who began sexing in the early 1950s, remembered:

“It was one of the top wages in those days. Even a carpenter used to make maybe $2.50 an hour. But if you were good at it, you’d have to do it guaranteed, at better than 98% correct. Usually you need to be at least 97% correct but if you go under that, you have to pay a penalty. If you make too many mistakes, whatever mistakes you make you have to pay back to the hatcheries.”

But this impressive pay was hard-earned, for, as Akune recalls, chick sexing was hard, tedious work:

“Maybe the hakujin (Caucasians) didn’t have any patience. Maybe the Japanese had more patience. You had to have a lot of patience. Sometimes you’d have 10,000 chicks behind you, so you had to go through 1,100 to 1,200 an hour. You had to go pretty fast. You had to work long hours, sometimes up to twenty-four hours without sleep, because you had to finish. You had a contract with a chicken hatchery, so you had to go around and after you finished at one place, you’d stop to rest and order a sandwich, and you’d be eating while you’re driving, and go to the next destination.”

These tight deadlines were integral to the work, since the older the chicks got, the harder it was to tell male from female. Ideally, sexing is performed within 12 hours of hatching, and with hundreds of hatcheries spread across the American Midwest, the life of a sexer involved driving vast distances to sex as many chicks as possible before the end of the short hatching season.

But while Japanese-Americans faced plenty of discrimination during the 1920s and 30s, the December 7, 1941 attack on Pearl Harbour and the subsequent American declaration of war against Japan made things much, much worse. Fearing that Japanese-Americans might be disloyal and aid their fellow countrymen by committing acts of espionage or sabotage, on February 19, 1942, President Franklin D. Roosevelt signed Executive Order 9066, ordering the forced removal and incarceration of all Japanese Americans from the West Coast. Hundreds of thousands of Japanese-Americans lost their homes and businesses, with around 120,000 being rounded up into purpose-built internment camps and many more fleeing to the Midwestern, Eastern, and Southern states. However, so vital were Japanese chick sexers to American agriculture that on the same day Executive Order 9066 was signed, a California state official warned the U.S. Department of Agriculture that their removal would seriously disrupt poultry production. He thus requested that the sexers be allowed to remain until the end of the hatching season in the spring, and that the Federal Government set about training white replacements. The DOA obliged, quickly setting up sexing schools at several institutions such as the University of California, but warned that the students would not be ready in time for the next marching season.

In 1943, the War Relocation Authority began distributing loyalty questionnaires which allowed Japanese internees deemed sufficiently loyal to the United States to obtain leave to work in other regions of the country. Of the chick sexers who fled eastward, most were able to find steady work thanks to the highly specialized nature of their work and the general labour shortage created by the War. Meanwhile, the FBI kept close tabs on these migrant sexers, suspecting that they might establish a line of communication from Japanese agents on the West Coast to the interior. Nonetheless, the unlikely skill of chick sexing allowed thousands of Japanese Americans to survive one of the darkest chapters in their history.

Following the end of the war and the abandonment of the internment policy, the Japanese chick sexing industry boomed once again. In 1947, West Coast refugees George and Ann Sugano founded the National Chick Sexing Association and School at 821 North La Salle Street in Chicago, whose two-year course cost $300 per year plus the cost of the chicks used in the students’ final examinations. Japanese-Americans who had served in the armed forces flocked to the school, as their tuition could be paid for through the Servicemen’s Readjustment Act of 1944 – better known as the “GI Bill”. At the same time, another school and professional association was opened in Atlanta, Georgia with the fantastic name Speed-o-Sex – no, really – but unfortunately this lasted only a year before going under. Nisei and Sansei chick sexers continued to dominate the American poultry industry for decades, providing much-needed income and a sense of pride to a beleaguered ethnic group. By the 1970s, however, the development of more efficient sexing methods and the consolidation of the poultry industry into massive factory farms gradually led to this once-thriving occupation becoming nearly obsolete. Thus, while once there were thousands of chick sexers, today there are only a few hundred working in Japan, the UK, and the United States.

Today, a number of alternate methods are used to sex chickens on an industrial scale. For example, starting in the 1950s, Reginald Punnett’s auto-sexing system was finally optimized for efficient meat and egg production, producing breeds like the California Gray, Rhode Island Red, New Hampshire Red, and Barred Rock chickens whose pullets and cockerels are easy to tell apart immediately after marching. For example, male Barred Rock chicks have a large, distinct spot on their heads, while Rhode Island and New Hampshire Red chicks with distinctive chipmunk-like stripes are almost always female. The chicks of other breeds can also be told apart thanks to the sex-linked silver/gold or Ss gene, which gives females a darker, browner down colour and males a lighter, more yellow colour.

Another common chick-sexing method is feather sexing, developed by New Zealand-based Tegel Poultry Breeding Company in 1969. This involves selectively breeding chickens so that the primary wing feathers of female chicks grow faster than those of male chicks. The two can thus be easily told apart shortly after hatching.

Finally, a now largely-obsolete method is instrument or machine sexing. This involves the use of a special sexing machine similar to the otoscope used by your family doctor to peer inside your ears. Just like vent sexers, machine sexers gently squeeze each chick to expel faeces from the anus, then insert the sexing machine into the cloaca and up the large intestine. A powerful light in the machine illuminates the interior of the chick’s body, allowing the sexer to spot the testes or ovaries – which have distinctive shapes – on either side of the spine.

Now at this point in the video, you might be wondering: what happens to the cockerels after they are sexed? Well, if you are the squeamish type or have a soft spot for cute animals, you may want to skip this section, because things are about to get grim.

Still here? Right: don’t say we didn’t warn you.

The simple answer to the question is: they are eliminated – quickly. The specific method of euthanasia has varied over time. At the National Chick Sexing Association and School in Chicago, male chicks were thrown directly into an incinerator. As Patti Sugano, a Nisei whose mother worked as a chick sexer in the 1960s recalls:

“I remember my mother telling me that somebody called the police, because they thought they were burning bodies in the building, because the way the chick sexing goes is that the females lay the eggs and are more valuable, so the young chicks that were males would just have to die and go in the furnace.”

According to Sugano, other disposal methods were also used:

“I remember my mother throwing a chick to one side or throwing the chick to the other side into a cardboard box which was for the girls, while males would sometimes go into a big steel drum, where they would suffocate. I also remember her bringing chicks home and she would have to drive them over to Lester Fisher (a Lincoln Park Zoo veterinarian), because the snakes ate live chicks. That’s just kind of the way it went.”

Today, at factory hatcheries like Hy-Line International in Spencer, Iowa – the largest such facility in the world – just-sexed cockerels are immediately thrown down a chute and ground up alive in a high-speed macerator… Over 30 million male chicks meet this fate at Hy-Line and similar facilities every year, understandably attracting angry protests from animal rights groups like PETA.

Thankfully, however, recently-developed technology promises to put an end to this horrific practice. In 2016, German scientists Roberta Galli of the University of Leipzig published a paper titled In Ovo Sexing of Domestic Chicken Eggs by Raman Spectroscopy. Galli’s method, developed as part of the punnily-named SELEGGT – a joint venture between the University, agricultural firm HatchTech, and German supermarket chain REWE, allows fertilized chicken eggs to be sexed after only 3.5 days of incubation. A laser is used to burn a 0.3 millimetre hole in the eggshell, through which a small sample of allantoic fluid is extracted. This sample is then treated with a special chemical marker and exposed to a certain wavelength of ultraviolet light. A particular colour change indicates the presence of the sex-specific hormone estrone sulphate, which indicates a female bird. Eggs with no estrone sulphate can then be destroyed or converted into animal feed without inflicting any suffering on the male embryos inside, which at this point have not yet developed a nervous system. In other words, thanks to modern technology it is now actually possible to count your chickens before they hatch.

The accuracy of the SELEGGT method has been measured at 90%, and while as of this recording no hatcheries have yet adopted the system, it promises to make the poultry industry – which in the United States alone generates over 100 billion eggs each year – just a little more humane and ethical.

And that, dear viewers, is the story of chick sexing, the obscure and highly-specialized skill that props up a huge swath of global agriculture and was instrumental in preserving Japanese culture in North America. Who knew?

Expand for References