Female caribou in Alaska’s Arctic National Wildlife Refuge are consuming shed antlers to replenish vital mineral stores lost during their arduous annual migration, a new study reveals. The research, published in the journal Ecology and Evolution, overturns previous assumptions about the purpose of female caribou antlers and sheds light on a unique survival strategy.
For decades, biologists puzzled over why caribou – too known as reindeer – are the only deer species in which females grow antlers. Theories ranged from defense against predators to establishing dominance hierarchies. Still, the University of Cincinnati study demonstrates that female caribou rely on antlers as a crucial “mineral reservoir” after completing a 1,500-mile round trip migration, particularly when raising calves.
“We knew that animals gnawed on these antlers, but everyone assumed they were mostly rodents. Now we know it’s really caribou,” said Joshua Miller, an associate professor at the University of Cincinnati and lead author of the study. “My jaw dropped when our results started to become clear.”
The research team analyzed 1,567 antlers collected from calving grounds within the Arctic National Wildlife Refuge. They found that 86 percent of the antlers showed signs of gnawing, with almost all the tooth marks attributable to caribou themselves. The antlers, composed of bone rich in calcium and phosphorus, provide essential nutrients during a period when other food sources are scarce.
“In the cold and dry climate of the Arctic tundra, shed antlers can sit undisturbed for hundreds of years,” explained Miller. “They are a source of nutrients that get revisited again and again.”
The timing of antler shedding is also significant. Female caribou typically shed their antlers within days of giving birth, making the mineral-rich resource readily available when nutritional demands are at their highest. The study highlights the importance of phosphorus, particularly for new mothers producing milk for their young.
Researchers also discovered that the caribou aren’t simply consuming a readily available resource, but are actively contributing to the ecosystem’s health. Minerals from the antlers leach into the soil, supporting the growth of grasses and lichens that form a key part of the caribou’s diet. “They are engineering this habitat, seeding the landscape with these super-important minerals that can be quite hard for animals to get enough of,” Miller said.
The Porcupine caribou herd, which inhabits the Arctic National Wildlife Refuge, was the focus of the study. Researchers collected antlers and bones during expeditions to the refuge between 2010 and 2018. Male caribou antlers can grow up to four feet long and weigh as much as 20 pounds, while female antlers are considerably smaller.
The findings offer a new understanding of the evolutionary purpose of female caribou antlers and underscore the intricate relationship between these animals and their challenging Arctic environment. The University of Cincinnati team plans to continue studying caribou behavior and nutrient cycling in the Arctic National Wildlife Refuge.