Caribou, large deer that are native to the northernmost parts of the world (and sometimes called reindeer), are the only deer whose females grow antlers. In a study published today, researchers observed behavior that might explain why: female caribou appear to gnaw on shed antlers as a kind of postbirthing supplement.
Caribou migrate huge distances every year between the places where they graze during the winter and the grounds where they calve in the spring. They can walk thousands of miles per year and likely have the longest terrestrial migration of any animal. Caribou mothers complete these extremely long migrations with antlers on their head and a calf in their womb. The period is very nutritionally demanding for them but culminates with a reserve stock of supplements when they need it the most.
The researchers behind the new study figured this out when they observed bite marks in more than 80 percent of the 1,500 caribou antlers that littered the part of the Arctic National Wildlife Refuge in northeastern Alaska where the deer give birth.
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“[Caribou] are just really going after the antlers. They are highly selective,” says study co-author Joshua Miller, a paleoecologist at the University of Cincinnati.
Female caribou shed their antlers just days before giving birth. Miller and co-author Madison Gaetano, a conservation paleobiologist, say that the findings suggest that female caribou are essentially banking nutrients in the form of antlers before they give birth and then gnawing on their freshly shed antlers to get a boost of protein, calcium and phosphorus they need to make up for having less time to graze as they nurse their calves.
“It’s a mineral that’s available to you at the time that you need it, and it presented as a very efficiently consumed resource, relative to forage,” Gaetano says.
There are other theories as to why female caribou have antlers. One is that these bony protrusions make the females resemble young male caribou and thus help them avoid aggression from older males. Another is that they use the antlers as a personal defense mechanism against predators. But antlers are on the ground for much longer than they’re ever on the body of the animal they came from, Gaetano says.
“It’s possible that [females’ antlers’ use as nutrition] is one of the reasons that they evolved, in addition to some of the other things that we think females are doing with their antlers,” says Danielle Fraser, a paleoecologist at the Canadian Museum of Nature, who was not involved with the study. “It can evolve to play multiple roles.”
Caribou antlers can remain on the Arctic landscape for decades and even centuries, preserving the evidence of how these bones are recycled back into the environment. The location of the bones and their condition can also tell scientists how a herd can change over time and may give researchers insight into how to help bolster caribou numbers, Miller says.
The study reveals that antlers are so much more than display items or something to fight with—they also seem to be a part of keeping young caribou families alive, Gaetano adds. “It’s so interesting to me just how creative animals will be in meeting their nutritional needs,” she says.