A Bit Different Anatomy Pullet or Cockerel?

The Curious Case Of The Misgendered Rooster

In the fall of 2021 Megan and David got four pullets from a friend and a cockerel from me. They recently sent me this: “Wanda has been a poor layer – kind of a freeloader of a very white egg , once a month. She hasn’t laid an egg since Christmas. In the last two weeks, we have noticed her comb has gotten huge and her tail feathers have sprouted. She looks like a full-on rooster. She is crowing up a storm, has pushed our rooster from his spot of prominence and is mounting the hens left and right. Do you have experience with this?”

They came to the right place because, of course, I did have an explanation for this phenomenon.

If you’re familiar with the chicken reproductive system you’ll know that hens have only one functional ovary – usually the left one. The right ovary and oviduct are present in female embryos, but don’t develop. If you pardon the pun, it is like putting all your eggs in one basket by relying on only one working ovary. So what happens if it gets damaged or diseased?

An ovarian cyst, tumour or diseased adrenal glands can cause the left ovary to regress and no longer produce the necessary levels of estrogen in the hen’s body. As estrogen drops to critically low levels, the hen’s testosterone increases triggering residual tissue in the right ovary to develop in the absence of the functional left ovary. This regenerated right gonad is known as an ovotestis and may contain some tissue characteristics of the ovary, testes, or both.

An ovotestis secretes androgen as well as estrogen. As a result, the hen develops male secondary sex characteristics: larger comb, bigger wattles, male patterned feathering, spurs and crowing.

Having heard the story of Wanda’s short, intermittent history of laying followed by an obvious transformation to rooster status I felt victorious in finding a well documented case complete with photographic evidence. What followed next was the last piece of documentation I needed.

I had told Megan and David that Wanda would end up a crowing, but non-laying, non-fertilizing, mating with the hens rooster. As Wanda, now renamed Juan, was becoming increasingly aggressive with both their other rooster and hens they felt it would be impossible to rehome her. They asked a mutual friend, Thomas, to euthanize her. I dropped by just as he was butchering Juan and had the forethought to ask if there was the presence of any testicles. Unfortunately I was too late to investigate any evidence of ovaries or an oviduct, but lo and behold, there were two undeniable testicles.

This is where I put the cart before the horse, the egg before the chicken or the hen before the rooster. I pride myself on presenting science-based information but in this case I fell short. In all my readings of the masulinization of hens it wasn’t entirely clear if in addition to developing secondary sexual characteristics (e.g. enlarged combs and wattles, crowing and mating with hens) could they also actually develop primary ones as well (i.e. testicles). The presence of Wanda’s testes appeared to be clear proof that they could.

I posted the claim complete with photos and then started really looking at the evidence and several ‘facts’ confused me.

  1. Megan and David are first time chicken keepers, but were sure that Wanda started life as a pullet because they had evidence in the form of eggs. Their other three hens all lay shades of brown shelled eggs and occasionally a pure white egg would appear in the nest box, which they attributed to Wanda.
  • I asked if they ever had four eggs in one day, which would support the idea that they had four hens. Since the white egg wasn’t laid regularly they weren’t positive, but thought they had.
  • Although Wanda was bigger than the other hens she had never crowed or demonstrated any rooster-like behaviour until she was just shy of a year old. This would be considered very late for a rooster to reach sexual maturity.
  • There was no clear information that I was able to find regarding masculinized hens’ ability to develop testicles. Some sources said no, while others said that because hens only have one functioning ovary then only the right gonad, which was previously dormant, would develop into a teste.

Gabe Campos posted on my Facebook thread: “I think it’s important to work back from an understanding of biology. We make hypotheses, look at the facts, then check the hypotheses. Our conclusion should come from the facts not the hypothesis.”

I couldn’t agree more. My stumbling block was that I had a clear understanding that mammals, including people, can be biologically neither fully what we label female or male, in that they may carry primary sexual characteristics of both sexes.  The phenomenon of starting out biologically female and transforming into a biological male does not occur in mammals, but I wasn’t sure about avian species.

I had the opportunity to ask my mentor, Dr Vicki Bowes, avian vet/pathologist if this was possible and she said it wasn’t in poultry. In peafowl, however, in rare it has been known that if a peahen carries vestigial embryonic testicular tissue this transformation can occur. So I was wrong about Wanda, but now know that it is theoretically possible in peafowl. Even then I would posit that we’re probably talking about intersex birds rather than biological females.

The long and short of Wanda’s case is she was always male, but a late developing one so as to confuse her inexperienced owners. What muddied things was the presence of an occasional white egg. My theory is this: all brown eggs are really white eggshells covered with brown pigment. I think that one of the pullets, who was a new layer, had pigment issues so that occasionally she produced a pure white egg and then sorted things out – hence no white eggs for the last six months.

There were a few lessons to be learned here: 1) it’s imperative to look at the science to back up our theories and not make assumptions, which might be based on erroneous ‘facts’, 2) it was a moment of humility for me, as I have now have had to backtrack, and hope that I am able to correct the misinformation I posted and 3) last, but not least, is Juan who got caught in the crossfire. Who knows how he would have behaved given different circumstances?

Thanks to Megan and David for their story and photo of Juan and of course to Dr Vicki Bowes for setting the record straight.

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