Unveiling the Mystery: Why Both Male and Female Reindeer Grow Antlers

It’s a common belief in the world of deer that males have antlers and females don’t, but reindeer serve as the exception. Both male and female reindeer grow antlers. This is a trait that no other species in the deer family possesses. The reason, a peculiar result of circumstances and biological luck, reflects how sophisticated the natural world can be.

Understanding Antlers

The terms antlers and horns are sometimes used interchangeably, but there are some distinctions between the two that are worth noting. Antlers are constructed of bone that’s chemically identical to any other bone in the animal’s body, although they’re protected by a sheath of keratin — the same protein that makes up our hair and our fingernails and toenails.

The primary difference between antlers and horns is that the former are seasonal while the latter are permanent. Antlers are the fastest-growing tissue on the planet, expanding at a rate of up to an inch a day. Antlers are made of bone and covered with “velvet”—a thin, soft layer of skin and blood vessels that gets scraped off the antler over time. Later in the year, those antlers are shed, making room for a new set to grow in. This dense coating lines the exterior of the growing antler and consists of blood vessels that provide the antlers with nutrients and help shield against the risk of infection. The bone grows outward as an extension of the skull.

Why Deer Grow Antlers

Deer grow antlers to compete for mates and protect their territory during rutting season. The growth and loss of antlers for most species of deer coincide closely with rutting season. In reindeer, males will begin growing their antlers in February and shedding them in November or December. This ensures that their antlers are at their largest and strongest during rutting season — approximately from late September into late October or November.

Why Female Reindeer Have Antlers

Female reindeer grow antlers that are significantly smaller than their male counterparts. Male reindeer grow antlers as long as 50 inches after multiple seasons of shedding. Females grow 20-inch antlers. Females shed their antlers in May, just after their calves are born but they begin to grow their antlers back later in the same month. This leaves a very narrow period in which female reindeer don’t have antlers, and it ensures that their antlers are at the fullest during the vulnerable months of pregnancy Reindeer herds are highly protective of their members, especially their young, but that doesn’t mean that there isn’t competition among females for resources.

A leading hypothesis for why female caribou evolved to grow antlers suggests their antlers are the result of evolutionary changes due to their habitat. Cold tundra with a notable lack of resources leads to a higher level of competition for food. This competition led to the development of more aggressive features in females, including antlers. In reindeer herds, females with larger antlers enjoy higher social standing and better access to food.

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