Why Do Roosters Crow?

Instructor: Stephanie Gorski

Steph has a PhD in Entomology and teaches college biology and ecology.

In this lesson, we will discuss the rooster crow. Topics include what triggers roosters to crow, what roosters communicate by crowing, and how roosters compare to their wild ancestors.

Rooster Noise Ordinances

Have you ever lived where you could hear a rooster crowing? Say you come from a moderately large city, where roosters are uncommon. But then you move to a small town and a rooster's crow greets your arrival to work almost every morning. For months, you assume that the rooster lives at the house next door to your building. But eventually you learn that the owners there don't know where the rooster's crow comes from either. You ask around, but the rooster's location remains a mystery.

A rooster's crow is very loud and can carry a long distance. Some observers have recorded the crow of a rooster at 98.5 decibels, much louder than a normal conversation's level of 60-65 decibels. That's why even in many municipalities where chickens are legal, people aren't allowed to keep roosters or they are more strictly regulated than hens. Perhaps the most unusual rooster law is found in Hopewell Township, New Jersey, where roosters are allowed, but only for ten-day 'conjugal visits' with hens.

Sexing Chickens

Sometimes, even people who are experienced with chickens misidentify cockerels (young roosters) as pullets (young hens). A rooster's crow is one of the most trustworthy methods of determining its sex. Roosters begin crowing at around four weeks of age.

The obvious differences between adult roosters and hens has led them to be an object of study for quite some time. Believe it or not, people were beginning to describe the effects of androgens (sex hormones) as early as 1771, all because of an experiment on roosters. Researcher John Hunter transplanted a rooster's testes into a hen. The hen survived and went on to grow a rooster's comb (the fleshy growth on top of its head) and wattles (the fleshy growth on its throat). In 1849, A. A. Berthold transplanted testes from a normal rooster into a castrated rooster. The castrated rooster not only grew his comb back, but he began fighting - and crowing.

When do Roosters Crow?

Most of us think that roosters like to crow before the crack of dawn. Indeed, they have the tendency to crow the most at that time. But would it surprise you if your mystery rooster crowed when you came to work around 9:30 in the morning, or during lunch, or even toward the end of the day? Roosters like to crow, and they can and will crow at any time.

What Triggers a Rooster to Crow?

Bright lights do trigger roosters to crow. Anecdotally, many people have noticed that roosters will sometimes crow when they see headlights from a car. The journalist Bernard Shaw even related that roosters were triggered to crow from the lights of bombs falling over Baghdad.

However, scientists have recently determined that the rooster's circadian rhythm, or internal body clock, is most responsible for his crow. Researchers at Nagoya University in Japan discovered that when roosters were kept indoors under constant conditions of 12 hours of light and 12 hours of darkness, the roosters would learn to crow about two hours before the light came on, regardless of what time that was.

The same researchers also set up an experiment in which roosters were kept in total darkness. The roosters would begin crowing about every 24 hours, regardless of the dark. This indicates that the roosters are triggered by their circadian rhythms.

However, the researchers found that circadian rhythms are not the only things that roosters use to trigger crowing. After about two weeks in complete darkness, the roosters' crows would become more irregular. This implies that roosters do need to see the light to keep their body clocks running properly. Roosters in these experiments would also sometimes crow in response to bright lights, but this happened more often during the time period in which they would crow anyway.

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