The moose (Alces alces) is the largest member of the deer family, a colossal herbivore. This imposing physical presence is a direct result of living in the harsh, resource-limited boreal and mixed deciduous forests of the Northern Hemisphere. Understanding the weight of a moose is not a simple number but a dynamic measure influenced by sex, geography, age, and the changing seasons.
Core Weight Statistics of Mature Moose
The general weight range for a mature moose is immense, though it shows clear differences between the sexes. Adult male moose, known as bulls, typically weigh between 380 and 700 kilograms (838 to 1,543 pounds) in prime condition. Mature females, or cows, are noticeably smaller, with weights generally falling between 200 and 490 kilograms (441 to 1,080 pounds).
The largest recorded specimens push these averages significantly higher. The largest confirmed weight for a bull was 820 kilograms (1,808 pounds), recorded for an Alaskan moose in the Yukon in 1897. There have been unverified reports of individuals scaling up to 1,180 kilograms (2,601 pounds).
Factors Causing Weight Variation
A primary reason for weight variability is sexual dimorphism, which causes bulls to be substantially heavier than cows across all subspecies. The heavy body mass of the male is an adaptation for the breeding season, known as the rut, where size is a factor in dominance displays and direct competition for mates. The weight a moose carries also changes significantly with age, with individuals typically reaching their maximum adult weight between five and eight years old.
Weight is also heavily influenced by the profound shift in available forage between seasons. Moose build up substantial fat reserves during the summer months when nutrient-rich aquatic plants and deciduous browse are abundant. During the harsh winter, when food is scarce and less nutritious, moose can lose a significant portion of their body mass. Males, in particular, may lose up to 20% of their body weight during the rut and subsequent winter period.
Subspecies and Geographical Differences
Weight is dramatically affected by the moose’s specific geographical subspecies, reflecting local environmental conditions and diet. The Alaskan or Yukon Moose (Alces alces gigas) is the largest subspecies and contributes to the species’ reputation for massive size. Mature bulls of this subspecies average around 635 kilograms (1,399 pounds), with cows averaging 478 kilograms (1,054 pounds).
In stark contrast, the Shiras Moose (Alces alces shirasi), found in the Rocky Mountain states like Wyoming and Colorado, is the smallest North American subspecies. Shiras bulls typically weigh between 370 and 544 kilograms (816 and 1,200 pounds). This difference highlights how localized habitat, which affects the availability and quality of browse, determines the ultimate size potential of a population.
Calf Weight and Growth Rate
A moose calf begins its life relatively small compared to its parents, weighing between 13 and 16 kilograms (28 to 35 pounds) at birth in late spring. This small size is quickly overcome by a remarkable growth rate in the first few months of life. Calves can gain over one kilogram (2.2 pounds) of weight per day while nursing on their mother’s milk and beginning to forage.
This rapid development allows a calf to multiply its birth weight by up to ten times within its first five months. By the time a calf is weaned in the fall, it can weigh between 136 and 181 kilograms (300 to 400 pounds), increasing its chances of surviving its first winter. However, a moose does not reach its full physical maturity and maximum weight until it is between four and six years old.