Do Female Reindeer Have Antlers? The Christmas Puzzle

The only deer with antlered females

In every other member of the deer family, from the white-tailed deer to the moose, antlers are a male feature used mainly for fighting and display. A female deer with antlers is a rare oddity, usually caused by a hormone imbalance. In the reindeer, antlered cows are normal.

Antler growth in deer is driven by male sex hormones (androgens). Research on reindeer suggests that the genes involved in antler growth are unusually sensitive to these hormones, so the lower levels found in females are enough to start the process. Even calves of both sexes start to grow small antlers in their first year.

Not every cow grows antlers. The share varies between populations. In many tundra herds the large majority of cows are antlered, while some forest-dwelling woodland caribou populations have many antlerless cows. Cows in poor condition may grow small antlers or none.

How cow and bull antlers differ

Like all deer antlers, reindeer antlers are made of bone and grow new each year. While growing, they are covered in a soft, blood-rich skin called velvet. Once the antler hardens in late summer, the velvet dries and is rubbed off.

Why female reindeer need antlers

The most widely accepted explanation is competition for food in winter. Reindeer feed in winter by digging craters through the snow to reach lichens and other plants. A good crater represents a lot of work, and stronger animals often push weaker ones away from theirs.

After the fall rut, the adult bulls drop their antlers. Pregnant cows still have theirs, and they use them to defend feeding craters against other reindeer, including large bulls. Antlered cows often rank highest in the winter feeding order, and studies have found that cows with antlers tend to be in better condition and to raise calves more successfully than cows without them. Keeping their antlers until they give birth helps cows secure the food they need while carrying a calf through the hardest months of the year.

Other ideas have been suggested, such as antlers helping cows protect calves from predators, but defending winter food is the explanation best supported by observations.

The yearly antler calendar

The timing differs between herds and regions, but a typical cycle for a tundra herd looks like this:

• Spring: bulls begin growing new antlers in March or April; young bulls and non-pregnant cows shed their old antlers.
• Late May to June: pregnant cows drop their antlers around the time they calve, then begin growing a new pair.
• Late summer: antlers stop growing and bulls rub off the velvet, usually in late August or September.
• Fall: bulls spar and fight during the rut, from late September to early November.
• Late October to December: large adult bulls shed their antlers; younger bulls keep theirs through winter.

Shed antlers are an important food for the tundra. Rodents, reindeer themselves and other animals gnaw them for calcium and other minerals.

The Christmas puzzle: are Santa’s reindeer female?

The reindeer that pull Santa’s sleigh were first named in the 1823 poem “A Visit from St. Nicholas,” and Rudolph was added in 1939. They are usually shown with big antlers and male names.

Real reindeer biology tells a different story. By late December, most adult bulls have already shed their antlers. A reindeer still carrying antlers on Christmas Eve is more likely to be:

• a female, especially a pregnant cow;
• a young male, which sheds later than older bulls; or
• a castrated male, since castration disrupts the normal antler cycle. Herders in northern Europe have long castrated male reindeer used for pulling sleds, because they are calmer.

So, if Santa’s team has antlers in December, it is probably made up mostly of females or castrated males. The story is folklore, but it is a good way to remember a real fact.

Caribou cows too

Because reindeer and caribou are the same species, wild caribou cows in Alaska and Canada grow antlers in the same way as herded reindeer cows in Scandinavia. The are reindeer and caribou the same? page explains the two names.