The gestation period in manatees lasts 11 - 14 months (USFWS 2001; Rathbun et al. 1995; Hartman 1979). Most calves are born from May through September, but young calves are observed throughout the year (Hartman 1979). Newborns average 1.2 - 1.4 m (4 - 4.5 ft.) in length and 30 kg (66 lbs.) (O'Dell 1981). Survival rates are low among the youngest calves, with half of all recovered carcasses (n = 1,212) from 1976 - 1991 belonging to Age Classes 0, 1 and 2 (Marmontel et al. 1997).Metabolism: In comparison to other large mammals, manatees have fairly low basal metabolic rates that measure only 36 - 50% those of similarly sized terrestrial mammals. This is perhaps the lowest weight-specific metabolic rate for any mammal known (Irvine 1983; Best 1981; Scholander and Irving 1941). Irvine speculated that low basal metabolism in the manatee may be an ecological adaptation of a large, tropical animal to a relatively low-quality food source.
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