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What is rut? Examining the annual elk ritual

Bugling bull elk is a sign of the annual rut season. Photo credit: Stan Powers.
Bugling bull elk is a sign of the annual rut season. Credit: Stan Powers.
By Christopher Johnson 
What is rut?
Instinct is the result of years of experience being handed down from generation to generation.  For elk, the act of rutting is an instinct that affects not only each individual elk’s life, but also the life of the entire herd. Mating and social hierarchy are arguably the two most important aspects of an elk’s life, both of which are influenced almost exclusively by the rutting period.
Timing is everything
Depending on factors such as latitude and elevation, the rutting period will occur anytime between August and October. The shorter days at this time of the year trigger the rut season, which runs through September and October.
“Bulls are sociable much of the year, living in bachelor herds. But as late August approaches, they separate and begin the process of gathering as many cows as possible,” explained Jim Zumbo in an “Outdoor Life” article about rut.
This process is known as building a harem — essentially each bull will now compete with one another to attract as many cows (female elk) as possible.
Bigger the better
Obviously, the bigger the bull’s harem, the greater chance they have of producing offspring. Bulls will usually have a harem of 15-20 cows, however, mature bulls can have a harem as large as 30 cows, according to the Purdue College of Planetary, Atmospheric and Earth Sciences.
The process of building a harem is incredibly competitive. Therefore, in order to build the largest harem possible, bull elk will utilize various instinctive behaviors such as posturing, sparring and perhaps the most notorious, bugling.
What’s that sound?
If you have been fortunate enough to live in Estes during the late summer and fall months, then there is no doubt that you have heard the mating calls of the bull elk, known as bugling. This distinctive sound is perhaps best described by the Purdue College of Planetary, Atmospheric and Earth Sciences as a “low-pitched bellow that intensifies to a loud, high-pitched trimodal note that continues until the bull elk runs out of breath.” This process will be repeated in order to maximize their level of seduction, and ultimately build a bigger harem.
Bugling is not limited to only mating purposes.  Dr. Jennifer Clarke of the University of Northern Colorado said that these sounds carry a “wide range of information.” Some calls can signal to cows that they have strayed too far from the herd, while others may warn competing bulls to be wary of their distance from the harem, lest they have to use their newly sharpened antlers for defense.
A visible sign that the rut season is about to begin is the shedding of velvet from the antlers of bull elk. The velvet is so high in nutrients that many elk will eat the velvet. The parts that hit the ground will be eaten by scavengers, so you will never likely find any velvet in the wild.
A visible sign that the rut season is about to begin is the shedding of velvet from the antlers of bull elk. The velvet is so high in nutrients that many elk will eat the velvet. The parts that hit the ground will be eaten by scavengers, so you will never likely find any velvet in the wild. Credit: Stan Powers.

Incredible, edible velvet
You may have noticed, either from being up close or via pictures, the soft coating on bull elk’s antlers. This is called velvet and it is not only vital for antler growth but is also incredibly rich in nutrients — so rich in fact that the elk will eat it as it falls off.

“Velvet helps protect the antlers and carries blood to the growing bone tissue,” the Rocky Mountain Elk Foundation explained in its materials. “If you look closely at an antler, you’ll see grooves and ridges on it. These mark the paths of veins that carried blood throughout the velvet.”
The blood will eventually stop flowing in August, just before the rut, and the velvet will begin to naturally fall away. To hasten the shedding of velvet, bulls will rub their antlers on anything that will help remove the velvet: trees, bushes, poles, and just about anything they can find to help remove the velvet.
The antlers of a bull elk are extremely important to the mating process. Not only do they serve the purpose of sparring with other males, but also the size of the antlers attracts the cows. Every year, the bulls will grow a new set of antlers and two factors go into aiding the development of a large set — a high-nutrient diet and an increase in testosterone levels. According to the RMEF, the “increasing daylight elevates the level of the hormone testosterone in the animal’s blood, which triggers the growth of antlers.” It is not until around October, when testosterone levels will start reducing and by early spring, the antlers will fall off and the process will start all over again.
The preorbital gland is always present on bull elk, but during rut season the gland will become much more prominent as it allows the secretion of pheromones that attract cows (female elk).
The preorbital gland is always present on bull elk, but during rut season the gland will become much more prominent as it allows the secretion of pheromones that attract cows (female elk). Credit: Stan Powers.

Preorbital gland
An up-close view of an elk’s head will show you a small slit just below the animal’s eye. This is the preorbital gland, and it is designed for one specific purpose — producing pheromone-based secretions. The gland stays closed most of the year, but will open when necessary.

“A rutting male may dilate its preorbital glands in order to signal aggression to another nearby male,” K.V. Miller explained in “Deer scent communication: what do we really know?” “Female deer often open their glands while caring for their young.
These glands are just another example of the tools elk will us in order to gain the advantage.
This story originally appears in the Estes Park Trail-Gazette.
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