Female caribou grow antlers as a built-in postbirthing snack

Female caribou grow antlers as a built-in postpartum snack

By Emma Gometz edited by Andrea Thompson

The caribou, a large deer native to the northernmost regions of the world (and sometimes called reindeer), is the only deer whose females have antlers. In a study published today, researchers observed a behavior that might explain why: Female caribou appear to gnaw on shed antlers as a sort of supplement after giving birth.

Caribou migrate large distances each year between the places where they graze in winter and the places where they give birth in the spring. They can travel thousands of miles a year and probably have the longest land migration of any animal. Caribou mothers make these extremely long migrations with antlers on their heads and a calf in their bellies. The period is very nutritionally demanding for them but ends with a stockpile of supplements when they need them most.

The researchers behind the new study realized this when they observed bite marks on more than 80 percent of the 1,500 caribou antlers that littered the part of the Arctic National Wildlife Refuge in northeast Alaska where the deer give birth.

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“[Caribou] They’re really attacking the woods. They are very selective,” says Joshua Miller, study co-author and paleoecologist at the University of Cincinnati.

Female caribou shed their antlers just a few days before giving birth. Miller and co-author Madison Gaetano, a conservation paleobiologist, say the findings suggest that female caribou primarily store nutrients in the form of antlers before giving birth, then gnaw on their freshly shed antlers to get a boost of protein, calcium and phosphorus they need to compensate for time spent grazing while they nurse their calves.

“It is a mineral that is available when you need it and presents itself as a resource that is consumed very efficiently compared to fodder,” explains Gaetano.

There are other theories as to why female caribou have antlers. The first is that these bony protrusions make females resemble young male caribou and thus help them avoid aggression from older males. Another reason is that they use the antlers as a personal defense mechanism against predators. But the antlers stay on the ground much longer than they ever do on the body of the animal they came from, Gaetano says.

“It is possible that [females’ antlers’ use as nutrition] “That’s one of the reasons they evolved, in addition to some other things we think females do with their antlers,” says Danielle Fraser, a paleoecologist at the Canadian Museum of Nature, who was not involved in the study. “It can evolve to play multiple roles.”

Caribou antlers can remain in the Arctic landscape for decades or even centuries, preserving evidence of how these bones are recycled through the environment. The location of bones and their condition can also tell scientists how a herd may change over time and can give researchers insight into how to help increase caribou numbers, Miller says.

The study reveals that antlers are much more than just display objects or a combat object: they also appear to help keep young caribou families alive, Gaetano adds. “I find the creativity of animals to meet their nutritional needs very interesting,” she says.

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