Bowhunting is rife with superstitions and lore. From how the moon affects deer movement during the rut to the factors that grow big bucks, deer behavior and biology spark big debates among bowhunters. A lot of data that hunters use is rooted in science. Other information is based on observations from time spent in the field. Some persistent beliefs stem from tall tales passed down at hunting camp. Most bowhunters develop their knowledge through a combination of these sources.
Understanding deer biology and behavior helps bowhunters pursue game more effectively. For example, many bowhunters try to plan their days in the field around the rut because certain rut phases increase deer movement, especially among older, more mature bucks that may elude hunters during other times of the season. This type of planning requires knowledge of what affects the rut. Longtime bowhunters may develop theories based on their experiences afield, but it’s important to incorporate science.
The Deer Ecology and Management Lab at Mississippi State University is a leading research facility that has published many unique studies and gained important insights into deer biology. Research from the Deer Lab says a deer’s breeding season, the rut, is triggered by the varying amounts of daylight and dark, called the photoperiod.
Deer Lab studies show white-tailed deer are “short-day breeders,” meaning the rut ramps up as day length declines and nighttime increases. A well-educated bowhunter can use this information to look at the hours of daylight and nighttime in the area they plan to hunt and adjust accordingly.
For bowhunters who want to understand the rut, the Deer Lab’s “Ecology of the Rut” is an excellent resource. It’s an in-depth look at all the factors that determine the period of peak breeding, and why this time frame varies across regions in the country. According to the Deer Lab, the bottom line is that “rarely will the timing of the rut change from year to year.” While this doesn’t mean there isn’t some variation, biologists say you can safely mark the same two-week period every year.
Deer Lab scientists say temperature and moon phase are not linked to the rut. This can be an unpopular opinion among some bowhunters. However, Deer Lab research has an interesting study that backs up this data. And it’s a case study that might surprise you. Recently, Lindsay Thomas Jr., the National Deer Association’s chief communications officer, revisited an old Deer Lab study. In Thomas’ article “What We Learned From a Buck With No Eyes,” he analyzes a one-of-a-kind study from the early 1980s.
In 1981, biologists discovered a Mississippi buck born with no eyes. This is a birth defect called anophthalmia. Biologists captured the buck and brought it to the Deer Lab. Retired biologist Dr. Harry Jacobson spoke with Thomas about how this unusual buck led to important scientific research on how photoperiod affects rut timing.
Without eyes, the buck’s brain had no way of receiving light. This provided an interesting opportunity for researchers to test the connection between light and antler growth. For the first five years of its life, the buck went through a normal antler growth cycle. However, according to the article, the buck “shed his antlers a few days later than the year before, and he shed the velvet of his new set even more days later each year. He averaged 378 days between antler casting and 373 days between velvet shedding. The two events grew slightly closer together but also later each year as time went on.”
Researchers noted that the blind buck did not have the same time frame for the antler cycle as normal bucks in the area. According to the article, “Those bucks cast their antlers on April 9 on average, but by 1986 the blind buck shed his antlers on May 19. While the average velvet-shedding date at the lab was September 24, the blind buck did not shed velvet until November 24, 1986.”
With five years of study in the books, researchers decided to make some adjustments. They wanted to see if simulating light levels to match what other bucks were experiencing in the area would shift the deer’s antler cycle to the same period as those other bucks. But how was that possible with a blind buck? According to Thomas, researchers were able to manipulate its levels of melatonin.
It was determined that deer are born with a natural breeding cycle, but the exact timing of the cycle is determined by the photoperiod. Photo Credit: John Hafner
Darkness tells the brain to create the hormone melatonin. You may be familiar with melatonin because some people take melatonin to help them sleep. In bucks, changing levels of melatonin signal breeding season. Researchers gave the buck a melatonin blocker to bring its levels closer to that of other bucks in the area.
“Immediately, the buck’s antler cycle shifted earlier and became consistent for two consecutive years,” Thomas writes. “Two years in a row he shed his velvet on the same day, November 11, and two years in a row he cast those antlers on the same day, May 5. Though the effect was not the same as the buck receiving actual photoperiod information, the test confirmed that manipulating melatonin levels – just as regular daylight cycles would – could adjust the timing of antler growth.”
The experiment, unfortunately, came to an end when the buck died at nearly 10 years old. But the blind buck provided some important insight for researchers. Ultimately, what does this blind Mississippi buck teach bowhunters? Whitetails are born with a natural rhythm that dictates the breeding cycle. That’s why even in the absence of light, the blind buck still went through a cycle of growing and eventually shedding antlers. However, the exact schedule of this cycle is determined by the amount of light in a day — the photoperiod.
How can hunters use this information? Next time you’re putting in for vacation days for bow season, you don’t need to wait to see what the weather does if you want to hunt the rut. Weather and the moon cycle change, but the length of the days will be about the same year to year. So, you might as well go ahead and ask your boss for roughly the same two-week period off every year. Other factors can impact movement and hunting conditions, but the blind buck teaches us that the length of the day is the most important determining factor.
