Can A Hen Turn Into A Rooster?

Today I went out to check on my hens, give them a treat, and pour some hot water into their waterer to thaw it out. The first unusual thing that happened was that as I stepped into their chicken tractor (a sort of mobile chicken pen) Harriet, my Rhode Island Red, flew at my hand which was holding their treat dish.

Harriet is usually the first one in line for treats, and she might hop up and down once or twice, but I have never had her leap up and land on the dish! I turned my head away (her beak was a little too close to my face for my comfort) and dropped both her and the dish to the ground.

I sat for a bit to watch them and make sure everyone seemed to be doing alright, since we're having a pretty unusual cold snap out here. And that's when I spotted a strange growth on the back of one of Harriet's legs. In fact, as I peered at it closely, it seemed to be… a spur!

There are a number of secondary sex characteristics in chickens. Larger wattle and combs, pointed hackle feathers (at the back of the neck), large sickle-shaped tail feathers, a more upright stance, more aggressive behavior, and spurs.

Spurs are a long claw which grows out of the back of the chicken's leg. Both male and female chickens have a rear toe (for a total of four toes). But roosters grow this extra claw, about an inch above the rear toe.

When I put this emergent spur together with Harriet's unusually aggressive behavior, I had to wonder!

Harriet was hatched in the spring of 2009, which makes her almost two years old. And I can attest to her hen-ness, since I have actually watched her lay an egg. So what's up with the spur?

Chickens - all birds, really - are a somewhat primitive animal, compared to mammals. Like other primitive animals (including fish, reptiles, and amphibians) it's not entirely unknown for them to change genders when the situation seems to call for it. When an all-female group of these animals is kept together, the most dominant animal will occasionally experience a gender change. The survival  value of this ability should be clear!

In the case of chickens, it is very rare for a hen to turn entirely into a rooster. Although it is possible! In one recent case, the photographic evidence is intriguing. I would be interested to find out if the chicken in question actually grew testicles, and was fertile.

It's more common for a hen to take on male characteristics. This is most likely caused by a hormonal imbalance. A similar hormonal imbalance in humans can cause women to grow facial hair, or men to begin to grow breasts.

Chickens who have a damaged ovary can sometimes be overwhelmed by the amount of unchecked testosterone in their system, and take on male characteristics (like spurs, or a larger comb). But the dominant animal in a flock will often take on male characteristics apparently simply because she is the "top chicken"!