Moose - Morphology 

Body Size

Moose exhibit a distinct sexual dimorphism in regard to body mass. Males can reach a maximum size of 1,650 pounds (750 kg) while females have a maximum weight of 1,100 pounds (500kg). However, females typically average between 880 and 990 pounds (400-450 kg) and males average between 1,435 and 1,545 pounds (650-700 kg). Females achieve maximum weight in early winter and around age 4, while males achieve maximum weight just before breeding season and between ages 7 and 9. Moose grow their entire lives, but no significant weight is gained after 4 years for females and after 9 years for males. As they grow older and begin to senesce, they lose body mass and become smaller. Weight change over time is also variant depending upon forage availability per year.

Bull moose lose 12 to 19 percent of their pre-rut body size during the breeding season, and 7 to 23 percent of pre-rut body size during winter. They will subsequently gain 33 to 41 percent of post winter lows (in weight) during the summer. Conversely, females live by a completely different schedule. They are at minimum weight shortly after giving birth which averages about 77 pounds lost birthing a single calf and nearly 140 pounds lost birthing twins. Gains in summer average 25 to 43 percent with 2-year olds gaining the most weight.

Length is incredibly variable and not well documented in the different subspecies throughout the country. No data is available on the Yellowstone Moose (Alces alces shirasi Nelson (1914)) but the Eastern Moose ( Alces alces Americana  Clinton (1822)) and Northwestern Moose ( Alces alces andersoni Peterson (1952)) have a total length of equal or greater than 9.2 feet (280 cm) and a shoulder height of 6.1 to 6.4 feet (185-195 cm). The Alaskan/Yukon Moose ( Alces alces gigas Miller (1899)) is slightly larger with a total length of 9.3 to 10 feet (283-306 cm) and a shoulder height of 6.2 to 7 feet (190-212cm).

Appearance

Moose coats range within the spectrum of brown shades but have been known to be black, rusty, and even albino or mottled on occasion. The hue will change depending on season. Bull moose typically develop a darker toned face during the fall due to male sex hormones. During winter, moose will exhibit a lighter colored coat. After winter, moose will take on a shabby appearance as they begin to molt. The frail, lighter hair will be shed, causing patches of dark skin on the head and shoulders to be bared. In the beginning of the summer, adults will have regrown their typical dark, glossy coat. Newborn calves have a tendency to have a rust colored coat of hair.

Photo Credit:US Fish and Wildlife Service
 

The coat is formed from two layers. The long, course hair, or guard hair, and the short, dense, wooly, bottom hair work simultaneously to regulate the moose’s body temperature. The hide also helps in regulating body temperature and protects the flesh from injury. The sebaceous glands secrete an oily/waxy matter called sebum to lubricate and waterproof the hair and cause it to remain supple, further increasing insulation. Sweat glands help to moisten the insulation properties of the skin and regulate internal temperature during the summer.

Antlers, formed from solid bone, are the key feature to sexing moose. Only bull moose exhibit antlers which can also be used to estimate an individual’s age. Typically, the oldest bull will boast the largest antlers. The size and shape also signify social dominance among bulls. Bulls will thrash brush or lock antlers and fight by pushing against other males to gain dominance. Antlers are covered in velvet which is rubbed off prior to the antlers being shed in November each year.

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