The Wild Animal Ritual Happening All Around Illinois — And Most People Don’t Even Notice

Deer rut is a biological spectacle that takes place every year in Illinois throughout the state with an estimated 660,000 individuals. And it happens without most of us even knowing about it.

Deer Rut Basics

In general, rut describes the behavior exhibited by males during the mating season for some mammal species. It is most often used for ungulates (hooved mammals) like deer, moose, and bison. During rut, testosterone increases in males to peak levels, making them more aggressive and hyper-focused on finding females, becoming less cautious and aware of their surroundings.  

What is deer rut in Illinois? 

In Illinois, deer rut refers to the rut season for the white-tailed deer (Odocoileus virginianus), the only native species of deer in the state. In addition to an increase in testosterone, males secrete scents from their glands, and during rut, these secretions become stronger to attract and communicate with females. 

White-tailed deer are sexually dimorphic, with the males being larger than the females, and they grow antlers. During rut in their heightened state of testosterone, males will fight with other males using their antlers to gain access to specific females. The largest male will assert dominance over other males and establish a social order. When males are more evenly matched, fights can become so intense that males can be found dead with their antlers twisted together. 

Peggy Anesi, an educator at Illinois Extension at the University of Illinois Urbana-Champaign, says that these large males will keep their antlers throughout the rut season. “The biggest males, the ones with the largest racks, physiologically keep their antlers longer than the smaller ones. Hormonally they function this way.” 

She described a situation in the past where she helped a resident who found a large male with a broken leg. Due to the broken leg, it could no longer participate in rut, and shortly after, his antlers detached. “He dropped his antlers because he couldn’t fight,” she recalls.

When does deer rut take place in Illinois? 

Rutting in Illinois typically takes place from October to January. The reduced amount of daylight increases melatonin, which ultimately induces estrus in females and increases testosterone in male white-tailed deer.

Rut essentially works backwards from the ideal conditions in spring for fawns to be raised. During spring, vegetation is lush and high in nutrients, ensuring a high-quality milk supply for mothers and thereby increasing survival rates in fawns. This is especially important for northern states like Illinois that experience severe winters, where if a fawn is born too early, it would have a smaller chance of survival. Gestation is about seven months for white-tailed deer females. 

Stages of Deer Rut in Illinois

Hard Antler Transition Phase (August-September): Males begin shedding the soft velvet covering their antlers, and antlers harden from an increase in testosterone. Velvet is the vascularized tissue surrounding the bone underneath. Males do this by rubbing their antlers against trees and other hard surfaces, and clearing these areas called “scrapes”. After a buck’s antlers harden, he is now capable of breeding for four to five months. 

Seeking Phase (Mid-to-Late October): During this phase, males begin to actively search for does entering estrus by assessing the pheromones in their urine and secretions from glands. These pheromones allow males to follow the females in later phases. Does will urinate and rub up against areas that males use to scrape their antlers. They may also make vocalizations such as grunts or light rattling to call in males. Males also communicate with females through scent-marking, conveying information about health, age, and fitness. 

Chasing Phase (Late October-Early November): Many does have now entered estrus and males are highly focused on mating and feed less. Males follow females, at times directly or with lag times of up to thirty minutes. Overall activity increases, especially at scrapes. 

Estrus Lockdown (Peak rut, approximately November 10- 20): The majority of does are in estrus and receptive to males. Activity slows down as males will stay near a single doe for upwards of 72 hours to breed with her several times and keep her separated from other males. Upon finishing this period, the buck will leave the doe and begin searching for other females to breed with again.

Second Rut (Early to Mid-December): Females that did not breed successfully will begin estrus again, 28 days after their first cycle, as well as a small percentage of females born that year breeding for the first time (fewer than 25%). 

Where to Watch Deer Rut in Illinois

White-tailed deer can be viewed anywhere in Illinois as this widespread species occupies every county, with the highest densities in the watershed wooded areas of the main rivers, notably the Mississippi, Rock, Illinois, and Kaskaskia, and also in the Shawnee Hills. As white-tailed deer are excellent at adapting to developed landscapes, they can be found in high densities in urban and suburban areas, remnant open spaces, and forest preserves.

When and How to Watch Deer Rut in Illinois

The best time to watch deer rut is from late October until early November during the chasing phase. As males are highly interested in females during this time and have likely not yet chosen a single female to stay with, as in the estrus lockdown phase, activity is high even during the daytime when typically deer are less active compared to dusk and dawn. If you see a doe during this time, almost always there’s a buck somewhere behind her. 

During the seeking phase from Mid to Late October, it is best to be downwind of doe bedding or feeding areas, in addition to areas in between the two, as bucks use scent to assess females’ readiness. Anesi says “You want to be downwind of a deer. If does smell you, they will run.”

During the chasing phase, rut is best observed in areas near scrapes. However, although activity is higher overall during the chasing phase, most activity still occurs during the night. During this phase, it is important to pay attention to behavior in does; if a female is overlooking her shoulder and her ears are alert, there is likely a male following her. 

Watching Deer Rut Safely 

Although deer are herbivores and theoretically pose no threat to humans, any animal has the potential to become dangerous, and this is especially true for males during rut when they have peak levels of testosterone that make them naturally inclined to fight with each other. This increased aggression can have spill-over effects. For example, a male may lose a fight with another male, become frustrated, and expend excess aggression on things in his environment, including human bystanders. 

This peak state also causes males to become hyper-focused on females, making them not only more aggressive but also less cautious and attuned to their surroundings. Males are more likely to partake in risky behavior, such as crossing roads. For instance, in 2022, over 40% of deer-vehicle collisions in Illinois occurred during rut, with November, when the chasing phase ends, being the month with the highest risk. Even if you are not directly involved in watching deer rut, it’s important to be aware of the rutting season as a driver on the road to avoid collisions. 

Although deer rut occurs in every habitat throughout the state, coming across such behavior is rare. To observe it, Anesi says, “You would need to be in a deer blind or go up in a tree stand.” If you happened to come across it, she adds, “Pay attention because you could get in the middle of it. If you see it, watch from afar. It is a phenomenon.”