Although similar, there are fundamental differences between reindeer and their wild cousins, caribou. Reindeer are shorter and stouter. Reindeer bulls are smaller than caribou bulls, but cows may weigh the same as caribou cows. Coloration differences may be too subtle to notice between many reindeer and caribou, however, reindeer tend to be lighter with occasional pinto or white haircoats. The nose bridge, or face, of reindeer are flatter than caribou.
Reindeer tend to stay in more cohesive groups.
When herded or chased they tend to run in a tight group, whereas, caribou are often scattered. These traits are the result of domestication. In Eurasia reindeer are classified as either domesticated or wild. Some female calves on the Seward Peninsula conceive at five months of age and calve as yearlings. Bulls usually don't breed until they're three years old.