If you ever analyze an image of a caribou (Rangifer tarandus) roaming out in nature, it might not even occur to you that physical traits can help you pinpoint the animal's gender. Since caribou, commonly known as reindeer, are sexually dimorphic creatures, however, distinguishing males and females can be a relatively straightforward task.
Size often makes distinguishing male and female caribou possible, as the males tend to be bigger than individuals of the fairer sex. Adult male caribou usually tip the scales in the ballpark of 275 to 660 pounds. The females are usually a little less substantial in size, with typical weights of between 50 and 300 pounds.
Caribou have the distinction of being the sole deer species in which male and female specimens alike are equipped with antlers. Although lots of female caribou sport antlers, exceptions do exist. You might be able to tell that a caribou is female simply by her lack of antlers. When female caribou do have antlers, they're generally nowhere near as big as the males' antlers. Male antlers also aren't as linear in growth as female antlers. The season also can assist in identifying gender. While male caribou lose their antlers in the winter, the females keep theirs all through the season into the spring. This helps expectant female caribou forage on the ground amidst all of the heavy snow and ice often covering everything.
Reproductive Season Physical Differences
During the reproductive season, male caribou take on some physical characteristics that make identifying their sex a lot easier, too. As they get ready to engage in fierce, often life-threatening battles for the attention of females, long hairs appear conspicuously below their necks. Their bellies also start pushing inward. Lastly, their necks begin taking on a somewhat larger and broader appearance. All of these things show up in anticipation for the fall rut, which begins in October and goes a little into November. The victors in the battles can select female caribou for their "harems." Harems are usually made up of between five and 15 female specimens.
Apart from the actual battles that take place between males during the reproductive season, other behaviors also can signify a caribou's sex. If a caribou runs after another, odds are strong that the individual doing all of the pursuing is the male, and the other, the female. When attempting to woo females, male caribou also frequently beat their antlers against shrubs.
- University of Michigan Animal Diversity Web: Rangifer tarandus
- IUCN Red List of Threatened Species: Rangifer tarandus
- Smithsonian National Museum of Natural History: Rangifer tarandus
- World Association of Zoos and Aquariums: Reindeer
- National Geographic: Caribou
- Denver Zoo: Reindeer
- San Diego Zoo Animals: Reindeer
- Tom Brakefield/Stockbyte/Getty Images