UCP Episode 018: Spontaneous Sex Reversal in Chickens – My Hen Just Became a Rooster!

Gynandromorph Chicken -photo by Roslin Institute @ Univ. of Edinburgh

Gynandromorph Chicken -photo by Roslin Institute @ Univ. of Edinburgh

Probably, if you have been following this podcast for a while now, you have noticed that I can’t get enough of the stories and news items that are based in the realm of the bizarre. Despite my clear predilection for that which is odd and curious, there is a deeper driving force behind today’s episode.   Oh, indeed!  This episode arises out of an actual situation and need I have based on recent behavioral changes in my favorite hen, Frida.  Her unexpected change — Frida is trying to crow like a rooster.  

Dr. Jacqueline Jacob - University of Kentucky Extension Program Manager

Dr. Jacqueline Jacob – University of Kentucky Extension Program Manager

Dr. Jacqueline Jacob is a poultry expert and joins us on this week’s episode of the Urban Chicken Podcast to explain the rare and bizarre condition by which chickens can reverse sexes.  This unusual transformation is called spontaneous sex reversal and it most commonly occurs in hens, causing them to physically transform into roosters. It is noteworthy that there are rare cases of roosters reportedly also being able to undergo sex reversal – thereby becoming hens and even laying eggs.  The cases of rooster to hen sex reversal is so extremely rare that it is not fully understood and is a topic that is still debated.

Chicken Innards - by sunshinewalks

Chicken Innards – by sunshinewalks

Spontaneous sex reversal occurs in hens when the left ovary is somehow damaged and can no longer produce the necessary levels of estrogen in the hen’s body.  As estrogen levels drop to critically low levels, the hen’s testosterone levels rise.  A hen whose body is testosterone addled will actually physically transform to take on male characteristics.  Such a hen will grow a larger comb, longer wattles, male patterned plumage and spurs.  The hen will also adopt rooster-like behaviors such as crowing.  Most shockingly though, once sufficient testosterone levels are reached, the hen’s dormant, gonad on the right side of her body is, for lack of a better term, “activated.”  When the dormant, right-side gonad is switched on, it develops into a male sex organ called an ovotestis.  Scientists have found that an ovotestis will produce sperm and this sexually reversed hen will try to mate with other hens in the flock.  It is however, unknown whether a hen that has undergone a spontaneous sex reversal and developed an ovotestis can sire offspring.

Dr. Jacob explains in detail spontaneous sex reversal in chickens on today’s show.  This is a crazy chicken topic and a fascinating interview.

Bilateral Gynandromorph Chicken

Bilateral Gynandromorph Chicken

In the Chicken News, I continue with the gender-bending theme of today’s episode and discuss an even rarer physical phenomenon called gynandromorphism.  A gynandromorph is a creature that has developed to be half male and half female.  The word gynandromorph comes from the Greek root words: 1) gyn (which means female), 2) andro (which means male), and 3) morph (which means state or form).  Scientists studying gynandromorphic chickens in Scotland originally thought that this unusual physical condition was the result of mutation. However, these Scottish researchers discovered that the gynandromorphic state in chickens was not caused by mutation but rather by half of the bird’s cells developing as female and the other half as male.

There are four main types of gynandromorphs: 1) bilateral, which is a left/right split of the female/male cells, 2) polar, which is a front/back split of the body’s female/male cells, 3) oblique, which is an X-shaped division of the female/male cells in the body, and 4) mosaic, which is a random spotty mixture of female/male cells throughout the body.

Gynadromorph chart - by Science Snaps

Bilateral, Polar and Oblique Gynandromorphism – by Science Snaps

Though gynandromorphism is rare in chickens – occurring in about 1 out of every 10,000 birds, it is arguably a more common condition than spontaneous sex reversal. Gynandromorphism is explained and discussed in much greater detail on today’s show.

In Sally’s Sidenotes,  I purpose to conduct a statistical/sociological study on spontaneous sex reversal in privately own chickens.  Listen in to find out how you can participate in this study.


  • BBC News – “Scientist Solve Half-Cock Chicken Mystery” ARTICLE
  • Natl Geo. – “Half-Male/Half-Female Chicken Mystery Solved” ARTICLE
  • BYC Forum-Photos/Info on owned Gynandromorph Chicken ARTICLE
  • Aus Journal of Zoology – Dbl Fertilization Causes of Gynandromorphism ARTICLE
  • Minnesota Birdnerd Blog – Gynandromorph v. Hermaphrodite ARTICLE
  • Science Snaps – “Gynandromorph – Breaking All the Rules” ARTICLE
  • StufftoBlowYourMind – “Dbl-Sex Chicken Wows Scientists” ARTICLE
  • OMG Facts – Some Chickens are Half-Male and Half-Female ARTICLE


  • Dr. Jacob’s Article explaining Spontaneous Sex Reversal ARTICLE
  • Dr. Jacob’s Small Flocks webpage LINK
  • Science Blog – Every Chicken Cell has Male/Female Identity ARTICLE
  • Live Science – British Hen Gertie that Became Bertie ARTICLE
  • CTV -Hen Sex Reversal-Owner Won’t Give Bird to Scientists ARTICLE
  • Univ of ID – Sex Reversal in Small/Backyard Flock Chickens ARTICLE
  • Aus. Poultry Sci. Symposium – “A Review of Sex Determination and Differentiation in Poultry” by M.H. Thorne JOURNAL ARTICLE
  • Pluck&Feather – Blog Post about Hen that Started to Crow LINK
  • UK DailyMail – “The Sex Change Chicken that Crows” ARTICLE
  • Med. Journal – Sex Reversal in a Chicken JOURNAL ARTICLE
  • Feathersite – Sex Change in Poultry PICTURES
  • “Strutting Super-Rooster is a Real Gender Bender” ARTICLE
  • Home to Roost – “It’s a Hen … or Maybe Not! ARTICLE
  • Rooster to hen: UK DailyMail – Rooster Lays Eggs! ARTICLE
  • Rooster to hen: Scientists Change Roosters to Hens ARTICLE


  • Urban Chicken Podcast’s Chicken Sex Reversal Study (Send me your info about your crazy chicken show sex reversal characteristics) CONTACT LINK 



Related Posts Plugin for WordPress, Blogger...