to lakes during the July–August dry season when water levels begin to fall, and are thought to fast during this period. Their large fat reserves and low metabolic rates—only 36% of the usual placental mammal metabolic rate—allow them to survive for up to seven months with little or no food. Feeding behavior Perioral bristles are not only used to sense things, but can be used to grasp and manipulate food. Macrovibrissae are used to detect food by its size and microvibrissae to manipulate food. They can be used to break off leaves and undesirable parts while the manatee is feeding. The snout makes up a muscular hydrostat, a biological structure that relies on muscular pressure and muscle contractions to manipulate and move food. The manatee uses its large upper perioral bristles to carry out a grasping motion: it performs a flare that tightens the muscular hydrostat while the large upper bristles get pushed out and the lower jaw drops and sweeps the vegetation in by closing. This is then repeated. Reproduction Despite being mostly solitary, sirenians congregate in groups while females are in estrus. These groups usually include one female with multiple males. Sirenians are K-selectors; despite their longevity, females give birth only a few times during their lives and invest considerable parental care in their young. Dugongs generally gather in groups of less than a dozen individuals for one to two days. Since they congregate in turbid waters, little is known about their reproductive behavior. The males are often seen with scars, and the tusks on dugongs grow in first for males, suggesting they are important in lekking. They have also been known to lunge at each other. The age when a female first gives birth is disputed, ranging anywhere from 6 to 17 years. The time between births is unclear, with estimates ranging from 2 to 7 years. In Sarasota, Florida, 53 females under observation produced at least 55 calves during a five-year period. Manatees can reach sexual maturity as early as two to five years of age. Manatee gestation is around one year, and then they lactate for one to two years. West Indian manatees and African manatees can breed year-round, and a female will mate with multiple males. Amazonian manatees have a breeding season, usually mating when the river levels begin to rise, which varies from place to place. Manatees in captivity Manatees may be taken