We should all have something to be thankful for at dinnertime today. But a newborn bottlenose dolphin at the National Aquarium in Baltimore has more than most.
The arrival of the male calf, born at the aquarium Sept. 9, has stimulated three unrelated females in his pool to produce milk. One of the three had never been pregnant.
Evidently charmed by the playful new arrival, two of the grown females have taken over the nursing chores from his biological mother, and he has nearly doubled his 36-pound birthweight.
The marine mammals' young trainers seemed just as entranced yesterday as they watched him push an orange basketball around the pool, swimming and playing with all his foster moms.
"I'm really excited for him," said Sue Hunter, the aquarium's director of animal programs. "He's doing so well, exhibiting all the behaviors we expect to see - and some we haven't seen before."
Most of all, Hunter is excited about the unexpected lactation and nursing behavior she has seen since the lad arrived. In a search of the scientific literature, she has found only three other reports of similar behavior in captive dolphins, and none quite like this.
"We're going to try to write a scientific paper based on his birth, growth and the behavior we've been seeing," Hunter said. "It really says something about how they survive" in the wild.
The calf was born to an 8-year-old named Jade, who arrived in Baltimore in October 2006 in a breeding exchange with Sea World in Orlando, Fla. Evidently, she was pregnant when she arrived.
"We didn't know that," said Allison Ginsburg-Kimmey, the aquarium's manager of marine mammals. But the pregnancy was eventually revealed by blood hormone levels and ultrasound exams. Paternity tests have identified the calf's father as an Orlando male named Sebastian.
After the birth, the calf and Jade were placed in a pool with three females: Shiloh, a dominant female; Shiloh's daughter Chesapeake, also an experienced mom; and 5-year-old Mango, who has never been pregnant. They were separated from the aquarium's male dolphins and several other females.
In the wild, Hunter said, related females and their young travel together, while mature males tend to live apart except during mating periods. The move was also thought safest for the newborn.
"I thought it would be the best-case scenario, to give all of us the best chance for the calf to survive and thrive," she said. "He's a tiny little guy."
In July 2004, a 4-month-old female calf named Bridgit died after she was roughed up by at least two grown males.
A necropsy revealed no bruising or broken bones. But the calf was found to be suffering from an infection. Aquarium officials speculated that a combination of male bullying and poor mothering by the calf's mother may have weakened her immune system and contributed to her death.
Dr. Joseph R. Geraci, the aquarium's senior director of biological programs at the time, vowed that after any future births, he would separate males from newborns and nursing females.
Almost immediately after the latest calf's birth, his inexperienced mom ceded her nursing duties to Shiloh, the dominant female of the group and an experienced mother. She quickly began what biologists call "relactation," which is milk production by a female who had previously been pregnant, but has now been dry for an extended period.
Soon, Shiloh's daughter Chesapeake, also an experienced mother, began producing milk and sharing some nursing duties. And Mango began "spontaneous lactation" despite never having been pregnant.
Jade's efforts at nursing, meanwhile, became half-hearted. Observers noticed that her mammary glands began to shrink, and signs of milk disappeared. She remained curious and interested in her baby, however, and in recent weeks has begun to play with him.
Shiloh does most of the nursing, and controls when the others can participate. But for a while there, Hunter said, "we had four milking mothers in here for him to choose from. It was pretty cool."
Both relactation and spontaneous lactation have been observed in other mammals, including horses, sheep, cows, goats and even humans, Hunter said. In 1975, a doctor reported relactation in a 55-year-old woman. She successfully nursed her orphaned grandchild 32 years after she last gave birth.
But only a few cases have been reported in captive bottlenose dolphins.
In 1995, scientists reported that two dolphins - both experienced mothers - began lactating a week after two orphaned calves were placed with them. Tests of their milk found that the fat content rose to normal levels.
A 1996 paper described a 5-year-old bottlenose that began lactating when another female in the enclosure gave birth, but the mother nursed her own infant.
No one is certain how this occurs - whether it is hormones in the water or simply a physiological reponse to the presence of an infant.
"It is of course survival of the species," Hunter said. If a newborn has several related females to nourish him, he is more likely to survive his mother's absence during hunting forays, or in the event of injury or death.
"The other reason is preservation of matrilineal lines" in a species where that is the core of social organization, she said. "Shiloh is allowing a related female to help raise this calf, even though the calf is not hers."
And for that he can be thankful.