Have you ever seen a monster buck and wondered how old the deer had to be to grow antlers that large? When hunters talk about deer records, record antler size and record weights for deer are common ways to denote size. But age is something that most hunters care less about- because most of the time, you don’t actually know.
The reality is that it’s a harsh life for deer in the wild. Bucks in particular face extreme challenges from competition with other bucks, and all wild deer are at risk of predation, disease, malnutrition, and other factors that contribute to mortality. So let’s dive into the different factors that can affect deer lifespan across the five native North American deer species.
Deer In The Wild
In the United States, we have five native species of deer: white-tailed deer (Odocoileus virginianus), mule deer (Odocoileus hemionus), elk (Cervus canadensis), moose (Alces alces), and caribou (Rangifer tarandus). Many of these species have subspecies, but we’ll keep things simple and just talk about them at the species level.
Understanding deer lifespan is more complicated for the non-whitetail species because there’s less data available. Whitetails have been studied extensively, even more so than mule deer. While both are popular game species, whitetail deer populations in the eastern US are of significant scientific interest. They have grown out of control in many regions due to the lack of natural predators, and thanks to the prevalence of certain diseases (more on that later), they’ve garnered more interest from the scientific community.
Wild Deer Mortality
When you look at deer mortality rates, white-tailed deer stand out as having much shorter average lifespans than other deer species. Why is this? There are many contributing factors to differential deer mortality. When we think about how long do deer live, we have to consider all of these contributing factors.
It’s hard to be a deer! Deer in the wild face numerous challenges that dramatically shorten their lifespans. Where captive deer are cared for and are safe from predators, wild deer often face harsh weather conditions and limited resources. This is especially true for eastern white-tailed deer populations.
Because their natural predators have mostly been extirpated, and because so much natural pasture space has been replaced by farms, many eastern deer survive the spring and summer only to die off in the winter, when their food resources become scarce. Winter water access is another huge problem for deer. During a deep freeze, they lose access to water, and can quickly dehydrate and die.
Climate also plays a big part in deer mortality. Deer do not live long in regions where there are severe weather conditions on a frequent basis. For example, the deer in Michigan’s upper peninsula where there are brutal snowfalls and winter temperatures, do not live as long as those in south Texas, where the weather conditions are temperate all year round.
Natural disasters can also contribute to deer mortality, especially forest fires. However, forest fires don’t contribute to deer mortality the way you might assume. Mule deer and elk populations bounce back quickly from forest fires, while white-tailed deer populations don’t. This is likely because of their diets; elk and mule deer forage on shrubs and grasses that increase after fires, white-tails eat plants like arboreal lichens that decrease after fires.
Hunting is one of the major factors that contribute to the drastic difference between the lifespan of deer that live in the wild and those that live in captivity. A publication by the Quality Deer Management Association Whitetail Report reported that hunting alone results in the death of 5.9 million white-tailed deer annually- and that’s just white-tails!
Another study from the Wisconsin DNR shows that hunting is more than 4 times higher than any other source of deer mortality. Deer do not live long in regions that have high hunting density- especially bucks.
Proximity To Roads
Annually, there are about a million and a half cases of deer involved in auto accidents. Most of these deer end up dying while those that are lucky enough to survive the accident are left injured, which makes them an easy target for predators, or can hinder their ability to find food.
Deer that live in the wild often fall prey to predators. This is especially true for young deer, which brings the average lifespan down.
Due to their wide range of distribution, coyotes are known to be the cause of a large portion of predation issues in areas throughout the white-tail deer range. A study carried out by the U.S. Forest Service Southern Research Station located at the Savannah River Site in South Carolina reported a total fawn mortality of about 70% at the site, and up to 80% of these kills were reported to have been done by coyotes.
However, other regions show much lower mortality; in Illinois, coyotes are only responsible for about 30% of fawn predation, Mountain lions, black bears, wolves, and bobcats are some other well-known deer predators. The most common predator for deer depends on the location you are considering.
Deer, just like humans and every other animal, can be affected by the outbreak of a disease. There are some diseases that are extremely problematic for deer; the three most prevalent are chronic wasting disease (CWD), epizootic hemorrhagic disease (EHD), and bovine tuberculosis (BTB). CWD is a prion disease that can affect all of the US deer species, but is most prevalent in the dense populations of white-tailed deer east of the Mississippi River. CWD affects the neurological system and is transmitted through saliva and bodily fluids, and has a 100% mortality rate.
The only treatment for this disease is hunting, believe it or not. Since there’s no cure and it’s difficult to control, the only real way to ensure it doesn’t have a massive outbreak is to cull infected animals and keep the herds at healthy sizes.
EHD is a disease transmitted through biting flies. Like CWD, it has no known treatment, and there is a high mortality rate. The outbreak of EHD varies annually and regionally, and it is most prevalent in the southeast.
BTB is a chronic and fatal disease that affects the respiratory system. It is less contagious than CWD and EHD, and is transmitted through the exchange of respiratory fluid, typically from sneezing or coughing. While BTB can be treated in domestic settings (it can infect other animals, like cattle, sheep, and interestingly, elephants), there is no treatment for wild deer.
So, with all of that in mind, what’s up with the white-tails? It’s a combination of factors. There are more white-tailed deer than any other species, and they are habitat generalists, not specialists.
They live in closer proximity to people, putting them at greater risk for car collisions. They’re hunted in greater numbers, and they are at greater risk for disease- especially in areas where they have few natural predators and have denser herds.
Deer In Captivity
In a game farm or ranch setting, however, deer can live much longer. They have constant access to food, veterinary care, and no predators. They are guaranteed to have enough resources to survive the winter, and they face less competition with each other, since their access to other deer is limited by humans.
For ranched deer, bucks in the 10-15 year range aren’t uncommon. Bucks in managed herds are kept alive longer, especially if they have great genetics that they can pass to the next generation. This is decided based on the size of the buck and the development of his antlers.
However, most age records for deer aren’t set on game farms; rather, they’re set at zoos. Zoos are less interested in traditional herd management and more in establishing high levels of individual care, so these animals tend to live longer than they do anywhere else. Here are the captive age records for the US’s native deer species:
- White-tailed deer: 23 years
- Mule deer: 22 years
- Elk: 26 years
- Moose: 18.4 years
- Caribou: 21.8 years
Interestingly, the oldest known moose, a 22-year-old doe, was a wild individual. Moose have few natural predators and typically experience less resource competition than smaller species, so they may live longer than other species.
How Old Is A Deer?
While being able to know how long deer live is interesting, what does that actually mean for hunters? Should they target older deer? Will older bucks be bigger bucks?
Not necessarily. While it varies a little bit based on location, deer typically stop getting bigger at around 3½ years old. Harvest data shows that most of a deer’s growth occurs between ages 1 and 2, and once they’re older, they only put on about 10% or less of their body size annually.
Antler growth is also not a reliable way to tell age. Bucks (and does, if you’re looking at caribou) grow their first set of antlers at about one year of age, and they grow a new set every year after that. With good nutrition, antlers will get larger each year until about six years of age.
There is a great amount of variation amongst individuals- a buck’s rack might not stay consistent from year to year. Aging via antlers only works for yearling deer and elk, since they have spikes instead of branches during their first year. If you really want to know how old a deer is, you need to look at its teeth!
Buck To Doe Ratio & How It Relates To Population
You’ll often hear about buck to doe ratios. This relates to how many bucks there are compared to doe. For example, a 1:5 buck to doe ratio means there is 1 buck for every 5 doe in that specific area. You’ll hear about this number when regions are thinking about controlling population, and overall age of the deer population of that area. There is a whole lot to go into depth on this subject. You can read more about the Buck To Doe Ratio here: https://tpwd.texas.gov/huntwild/wild/game_management/deer/age/