Archive for May 3rd, 2010

It’s a Hen… or Maybe Not! Gender-Bending Chickens

One of your hens suddenly stops laying. Her comb and wattles enlarge, and (s)he starts crowing… WHAT is going on?

Weird science, yes. And other people have found it weird, but they did not consider it to be science—Gail Damerow reports in The Chicken Health Handbook that, in 1474, a rooster named Basel was burned at the stake for laying eggs.

Normal Physiology

A hen has two ovaries. Normally the left ovary atrophies during development of the chick, and only the right ovary produces eggs. However, in some rare and bizarre cases, alterations in the bird’s ovaries cause sex hormone changes.

Female Changing to Male

On rare occasions, the right ovary ceases normal function—perhaps due to a tumor or an infection, and the left ovary becomes functional, sometimes producing testosterone. This hormone switch causes the bird to develop typically male features: larger comb and wattles, male plumage, male vocalization.

For some fowl gender-benders, check out these photos.

Male Changing to Female

Then there is the recently reported bizarre story of the Italian rooster, Gianni, whose flock of hens was lost to a fox raid. Gianni became Gianna and started producing eggs!

The article cites a “bizarre DNA mix”; however, I posit that the bird’s genetics are not the issue. The bird’s genotype did not change; only the phenotype (expression of the genes) is altered.

Perhaps the right ovary was initially nonproductive, causing a testosterone-laden female bird with male sex characteristics. The right ovary then decided to quit the picket lines and return to production, et voilà – a rooster-turned-hen!

However, further reading indicates that it is highly unlikely that these birds will ever assume the full reproductive roles of the newly acquired gender.

Practically Speaking

For those of you who are content with your two backyard hens who quietly sing and cackle occasionally, no need to panic about being woken in the middle of the night to crowing. This is not a common phenomenon! But if Henrietta suddenly starts acting like Henry, please don’t burn him/her at the stake. The only devilry going on is hormonal!


Daily Mail Reporter. April 22, 2010. “Now I’m a chick! Gianni the gender-bending cockerel starts to lay eggs, baffling scientists.”

Damerow, Gail. 1994. The Chicken Health Handbook. Storey Publishing: North Adams, MA.

Jacob, J. and F. Ben Mather. “Sex reversal in chickens.” Factsheet PS-53. University of Florida Extension: Institute of Food and Agricultural Science.

“Sex Change in Poultry.”