All About Antlers!

Spring visitors to Yosemite, looking around and seeing only deer with no antlers, sometimes ask rangers, “Where are all the bucks?”

People more familiar with deer will know that bucks lose their antlers in late winter and regrow them over the course of the spring and summer. So when you see a deer in March, whether male or female, you won’t see those characteristic antlers.

Pause for just a second to think about how amazing it is that these animals regrow and then shed their antlers every year. Deer antlers are unlike anything else in the mammal world. They are among the fastest growing tissue in the entire animal kingdom. They are not just majestic, but also fascinating to medical science and to casual observers like us! 

And that’s just the beginning. Did you know scientists can get mice to grow antlers? Do you know about the unique antlers of Yosemite’s most famous deer ever? Did you know that some Asian deer don’t have antlers at all, but something much scarier?

Look at these two guys below who stopped by the house on April 26 with just their short spring antlers. We don’t know at this point how large these antlers will get.

A healthy, mature male with excellent nutrition will grow these out to a majestic “rack” with over three feet of “spread” by September. Mule deer average about a quarter to a half inch per day of antler growth throughout spring and summer.

Other members of the deer family (Cervidae) are even more impressive. In a single day, elk can grow an inch of antler and moose can add a full pound. Still, this is nothing compared to the extinct Irish Elk (actually a deer, not an elk). It could grow and regrow antlers up to twelve feet (3.5m) across.

Skeleton of Megaloceros giganteus
The massive antlers of the extinct deer Megaloceros giganteum in the National Museum of Science and Nature in Tokyo, via Momotarou2012 on Wikimedia under the Creative Commons 3.0 License with various lighting adjustments.

Just how do they do that?

That’s just what scientists trying to understand bone growth, regeneration, and other basic science questions want to know.

Wait, Antlers are Bones?

Yes! Antlers are bones. People sometimes confuse antlers with horns, but they are very different. Horns are mostly keratin, the protein that makes up hair, claws, hooves, feathers and, yes, horns. Horns are found on both males and females, grow continuously, are permanent, hollow, and grow from the base. They are found in cattle, bison, buffalo, sheep and several other mammal families.

Antlers are altogether different. Antlers are unique to deer and only found among males except in reindeer, including caribou. Most uniquely, though, they are shed and regrown every year.

That requires a significant outlay of energy and nutrients for the male deer. Just like other bones of the body, the thickest part of the antlers have a spongy interior that contains bone marrow, which is where the body makes blood cells. In other words, the antlers are full-fledged bones that do all the things bones do.

During the growing phase they are soft and made up mostly of water and protein. They are covered with “velvet” that is rich in nerves and blood vessels. As summer ends, antlers stop growing, mineralize and harden in time for “rutting” season when the bucks use their antlers to compete in pushing contests. The winner is the one who gets to mate.

Wondrous Velvet

Close-up of mule deer face with velvet still on the antlers, deer facing the camera
Mule deer at Housekeeping Camp in Yosemite Valley. Note the velvet. The antlers perhaps half grown out in this June photo..

The fuzzy velvet that covers a deer’s antlers during the growth phase is how all the nutrients get to those growing bones. Because these growing antlers are mostly water and protein, they are relatively fragile.

So in addition to having a rich blood supply, the velvet is full of nerves and highly sensitive. In fact, it’s so sensitive that deer can be seen gingerly avoiding branches and brush in order to avoid injuring the velvet. This helps ensure they get a nice, symmetrical rack to increase their chances of mating in the fall.

We might think that antlers are a formidable weapon for defense, but that’s only true once they harden and shed their velvet. Their main purpose is to challenge other bucks during the rut and to display dominance, not to fight off coyotes. If a buck in the velvet phase is forced to fight off a predator, he will actually fight with his hooves and protect those antlers from damage. They are too precious to risk in a fight, and too soft and too sensitive to be effective anyway.

It is only late in the season, when the antlers are fully formed and hardened and ready for contests with other bucks that the velvet dies and falls off. And what does a deer do with that discarded velvet? It eats it. Can’t let all that good protein go to waste!

Mule deer with dying velvet shedding off antlers
Velvet sheds once antlers fully harden (NPS Photo, public domain)

The Life Cycle of a Yosemite Deer’s Antlers

Of course, this cycle is more or less the same everywhere, though the timing might differ a bit here and there due to climate.

  • March. Bucks shed antlers as early as January, but rarely. Shedding is most common in March.
  • April. New growth starts 2-4 weeks after shedding.
  • July. First forking of antlers is achieved. Before this, all bucks will have just a single spike. Once they reach full size, they will begin to harden and mineralize.
  • September. Antlers have grown to full size and strength. At this point the velvet dies and bucks then start “horning” brush and trees to scrape it off.
  • October or November. Necks swell to prepare for rutting contests.
  • November to January. Rutting Season. Mostly a pushing contest where the goal is to drive the rival to his knees. Once achieved, the dominant male “runs” a female for several days until she lets him mate with her. Once that’s done, he starts running another female. This lasts into January, sometimes into February.
  • Once the mating season is over, the bucks shed their antlers and the cycle starts all over again.

Notice in the photos below how the bucks sparring in the top photo from September still have thin necks. In the second photo, where they are in it for real, the necks have thickened and are ready for the real contest.

Where Do All the Antlers Go?

The deer population of Yosemite probably numbers in the thousands. If only a thousand bucks are shedding 2,000 antlers every year, where do they all go? You would think that 2,000 antlers shed year after year would start to become a bit of nuisance. Why don’t we see them all the time on hikes?

There are a few reasons. The first is that the deer don’t follow our trails, so a lot of the antlers end up in places humans don’t frequent. In addition, the deer often go to lower altitude to shed antlers. Still we see deer tracks in our area all winter, so they must be shedding antlers in our area.

So after many years, shouldn’t there be antlers everywhere?

Mature, hardened antlers are about 40% protein and 60% minerals. That makes them a great nutritional supplement for squirrels and other rodents who do not have subscriptions to Amazon Prime and can’t get their calcium supplements delivered by UPS. Also, rodents need to gnaw in order to maintain their teeth. When they find an antler, they gnaw on it. Porcupines are particular fans of deer antler, but in our area they only inhabit the lower reaches of the deer’s range. That leaves squirrels as the great recyclers of all that calcium, phosphorous and protein tied up in deer antlers. And thanks to them, the woods are not littered with years of antler accumulation.

Ground squirrel in Curry Village
Ground squirrel in Curry Village. Thank his kin for taking on the job of cleaning up all those antlers the deer litter throughout the park every year.

What would happen if there were no squirrels? It turns out that we know the answer. The squirrel population of California generally and Yosemite in particular was devastated by disease in the early 1920s. For years at a time into the 1930s, as few as a single pair of squirrels were seen in Yosemite Valley. The grey squirrel almost went extinct in much of California. In 1925, a few years after the collapse of the squirrel population, park naturalist Carl Russell went walking an area where deer were known shed antlers. He found more than two dozen single antlers in less than a mile without leaving the trail. Without the squirrel helpers to break down the antlers, they apparently did start to accumulate in the 1920s.

Antlers and Medical Science

Antlers are the only appendage that any mammal regenerates. They also grow faster than almost any tissue in the animal kingdom and are probably the fastest growing bone in the world. You can see why scientists are interested in antlers. If we understood antlers better, we might conceivably be able to regenerate a lost finger, heal broken bones faster or prevent and reverse osteoporosis.

Scientists have long known that there was something special about the cells at the base of the antler, the pedicle, from which the antler regrows every year. In the 1960s, researchers transplanted pedicle cells to the leg of a deer and it started to grow an antler on the leg! Even more surprising, they have transplanted pedicle cells to the forehead of a mouse and guess what? The result is this somewhat disturbing picture of a mouse with a sort of unicorn in its head. Do not try this at home!

Lab mouse with "antler" between the ears
Mouse with transplanted antler stem cells. Image from “Tissue Interactions and Antlerogenesis: New Findings Revealed by a Xenograft Approach,” by Chunyi Li, A. John Harris, and James M. Suttie, Journal of Experimental Zoology 290:18–30 (2001)

More recently, scientists have discovered the key genes that allow the deer to grow bone so quickly. In 2018, researchers at Stanford identified one gene that promotes the exceptionally rapid growth of antlers and another that promotes the exceptionally rapid hardening of antlers. Both of these genes are present in humans and linked to bone development. Understanding them better could lead to therapies for osteoporosis and other bone diseases.

And that’s not all. There could even be implications for cancer research. Why can’t other mammals regenerate appendages? Nobody knows for sure, but deer commonly suffer from deformities or uncontrolled growth of their antlers. It appears there might be some sort of tradeoff. You can have rapid growth and regeneration, but it might come at the cost of being more susceptible to that other form of rapid growth, cancer. So the study of deer antlers might have clues to what causes runaway cell growth and how to control it.

More Fun Facts About Antlers

  • If a deer is injured in the right front leg while the antlers are growing, the right antler will be deformed or stunted. But if the deer is injured in the right hind leg, the left antler will be deformed or stunted.
  • Mule deer antlers can weigh over 30 pounds, much of which is calcium.
  • To get all the calcium they need for their antlers, deer take it from their own bones, by preference non-weight-bearing bones like ribs. This means they get temporary osteoporosis every year.
  • Antlers have been important to humans for thousands of years – they are one of the primary tools used for flintknapping, that is making arrowheads, spearheads and the like from flint and obsidian.
  • The number of points on an antler do not indicate the age of the deer. In general, antlers get larger with age up until about 5.5 years old (the buck’s sixth summer) then stabilize. As a deer ages they can get smaller each year.
  • Age is only one determinant of antler size. The other big one is nutrition. Calcium is important, but during the growth phase antlers are mostly protein, so protein availability really affects antler size.

And the Really Crazy Stuff

If you’ve made it this far, now we get to the really crazy stuff! Here’s a quick bit about Yosemite’s most famous deer and deer species that don’t grown antlers at all, but something much scarier looking.

Yosemite’s “Rhino Buck”

Unquestionably, the most famous deer in the history of Yosemite was an ancient old buck people called Old Horny. He got his name because he had a third antler growing out of his forehead. Three-antlered deer are rare, but not unheard of. Typically, however, the third antler grows out of the frontal bone like the other two. Old Horny is believed to be unique in that his third antler grew out of the nasal bone.

He was much beloved by visitors in the 1920s who frequently fed him buttered toast, back when feeding the animals was a standard part of a national park visit (please don’t revive that tradition!). When he finally died, it was discovered that he was exceptionally old. His teeth had been ground all the way down to the gums, a sign of extreme old age in a deer.

That’s not a surprise — antler deformities are more common as deer age and Old Horny’s twisted antlers were another testament to his advanced age.

Saber-toothed Deer?

What could be stranger than a three-antlered deer? How about a saber-toothed deer! If you live in parts of Asia where the water deer come from, or in the UK where they are considered invasive, you might know about deer with tusks. For most of us in North America, though, the thought of innocent little Bambi with deadly tusks is a bit unsettling.

Stuffed Chinese water deer head with tusk
Bambi would have been a much less heartrending story if Bambi had sported tusks like these!

How in the world do you end up with a saber-toothed deer? There are in fact several species with tusks. It turns out, that antler size correlates to the size of the animal and, below a certain size, antlers are just not effective fighting tools. All the deer with tusks are under 15kg.

They also live in dense forests or jungle and are solitary rather than herd animals. This is important because antlers allow for bloodless competition among bucks. Herd animals do not want to shed blood, because they do not want to draw predators to the herd. Also, deer with antlers tend to live in open areas where they can display their large antlers from a distance as a dominance display. In tight vegetation, there’s no advantage to a big rack visible across distance and it just gets hung up in the vegetation. So these small, solitary jungle dwellers have tusks.

It turns out that ancient deer may have had both tusks and antlers, but as they evolved, one came to dominate based on the size, habitat and social life of the deer. However, even our nice Bambi mule deer have to potential to grow tusks. On occasion, hunters who kill a mule deer find that in fact it has canines up to an inch long. In other words, the basic genetics for tusks remains latent, it just is not expressed since antlers are so much more useful in the places mule deer live, like Yosemite.

All of that is somewhat theoretical, but it’s the best guess of the scientists who published the wonderfully-named most recent research article on this: “Stabbing Slinkers: Tusk Evolution Among Artiodactyls,” by Doreen Cabrera and Theodore Stankowich in Journal of Mammalian Evolution, Vol. 27, Iss. 2,  (Jun 2020): 265-272.

Wrap Up: Your Turn.

I hope all that deepens your knowledge of our deer, and yours too if you have them near your home. I also hope that the images of the “stabbing slinkers” will not trouble your dreams!

There’s a lot more one could say about antlers, but maybe we already said too much. Our goal with these articles is to expand people’s knowledge and appreciation of the natural world around them. We find these explorations interesting, but maybe you would rather read about different things. If you have ideas for things related to Yosemite nature or history that you would like to read about, let us know by email or in the comments. We would love to read your suggestions!

Read More

There are countless articles about antlers on everything from the Smithsonian website to hunting blogs. A lot of state departments of wildlife have nice pages too. These are some fun articles as well as some of the more esoteric, academic sources that played into this article.

Fun and not too scholarly:

A bit on the more esoteric side: