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Reproduction and life cycle

Reindeer mate in late September to early November, and the gestation period is about 228–234 days. During the mating season, bulls battle for access to cows. Two bulls will lock each other's antlers together and try to push each other away. The most dominant bulls can collect as many as 15–20 cows to mate with. A bull will stop eating during this time and lose much of his body fat reserves.

To calve, "females travel to isolated, relatively predator-free areas such as islands in lakes, peatlands, lake-shores, or tundra." As females select the habitat for the birth of their calves, they are warier than males. Dugmore noted that, in their seasonal migrations, the herd follows a female for that reason. Newborns weigh on average 6 kg (13 lb). In May or June, the calves are born. After 45 days, the calves are able to graze and forage, but continue suckling until the following autumn when they become independent from their mothers.

Bulls live four years less than the cows, whose maximum longevity is about 17 years. Cows with a normal body size and who have had sufficient summer nutrition can begin breeding anytime between the ages of 1 and 3 years. When a cow has undergone nutritional stress, it is possible for her to not reproduce for the year. Dominant bulls, those with larger body size and antler racks, inseminate more than one cow a season.