Q. How many babies does a mother manatee usually have in her lifetime?
--Sophia Ng, Canada
A. In order to answer this question, we will need to discover and understand four key elements of a manatee’s reproductive biology.
- The age at which females reach sexual maturity and can successfully produce offspring.
Female manatees become sexually mature at about five years of age, but there has been evidence of manatees giving birth as early as three years old.
- The length of time between birthing calves, also known as the calving interval.
Manatees most commonly have a calving interval of two to five years. The calving interval is influenced by a variety of factors, such as age, and therefore can greatly vary among individuals. A lower calving interval occurs when a female loses her newborn calf soon after birth.
- The number of calves a female can give birth to at one time.
Usually, manatees only give birth to one calf at a time; it is possible for a manatee to give birth to twins, but this is rare. According to Mote Marine Laboratory, twins are born between 1.4 and 4 percent of the time for the Florida manatee. The gestation period for a manatee is about 13 months.
- The lifespan of the female manatee.
The oldest a manatee can live to be is between 50 to 60 years old. Unfortunately, most manatees in the wild do not live past 30 years old.
Now for a little bit of math!*
On average, if a female manatee becomes sexually mature at 5 years old, has a calf every 3 years and never has twins, and lives to be 30 years old, she will have 8 to 9 calves in her lifetime.
A conservative estimate for a manatee that becomes sexually mature at 5 years old, has a calf every 5 years and never has twins, and lives to be 30 years old, would be that she would have 5 calves in her lifetime.
On the high end of the reproductive spectrum, if a female manatee becomes sexually mature at 3 years old, has a calf every 2 years, gives birth to one set of twins, and lives to be 30 years old, she may have up to 14 to 15 calves in her lifetime.
*These calculations do not include a death of a manatee calf soon after birth, which may result in a shorter calving interval. Nor do these calculations account for the fact that, unfortunately, many manatees do not live to reach age 30, or even to reproductive age, because of mortality from watercraft collisions and other human and natural causes.
Some of our manatee adoptees are known mothers, including Phyllis, one of our Blue Spring adoptees, who gave birth to twins in 1991. Phyllis was born in 1985, and, in addition to birthing the first recorded twins at Blue Spring State Park, has raised an estimated 12 additional calves. One of Phyllis’s calves, Phalcon, has had 5 calves. Another Blue Spring Adoptee, Lily, has had at least 11 calves and is a great-grandmother! Lily’s daughter Lillith has had 9 calves, and Lillith’s daughter, Laurie, has had 4 calves of her own.
In addition to giving birth and raising their own calves, manatees can also adopt calves that are not their own. Without this behavior, these orphan calves would be unlikely to succeed in the wild. Calves remain with their mothers for up to two years, during which time they learn important survival techniques. Therefore, it is beneficial to the survival of orphaned offspring to become adopted by unrelated female manatees. Many of our manatees in the adoptee program, like Georgia and Rosie, have also served as surrogate mothers to many orphaned or injured manatee calves.