On December 3, 2000, at Cape Shirreff, near the tip of the Antarctic Peninsula, a female Antarctic fur seal experienced a personal tragedy: She gave birth to a dead male pup. For the next day or so, the seal, numbered “12” by scientists watching her group, nuzzled her baby and vocalized to him.
Nearby on December 4, another female, No. 29, gave birth to a live male pup. But soon she, too, experienced a traumatic event: No. 12 kidnapped her pup.
Scientists have been studying this population of fur seals for decades, and this behavior was odd. In some species of mammals, it’s not uncommon to find moms sharing child-raising duties. But Antarctic fur seals don’t do that. Mama seals give birth to one pup a year and take care of it for up to four months, keeping track of her offspring in the large seal colony by taking note of its appearance, smell and vocalizations. Helping out another seal doesn’t happen.
When the researchers watching this population of seals came by on December 5, they found that No. 29 did not have a pup. She called and called and called for her baby.
Strangely, No. 12 had a live pup with her, along with her dead baby, which she continued to nuzzle. The scientists captured the live pup, weighing and measuring it for their study, and marked it with a “12,” thinking that she was its mom. But after noticing 12’s behavior with the dead seal, they concluded that the live pup belonged to 29 and returned it to its distraught mom.
“After a few minutes, female 12 kidnapped the pup and kept him with her,” Jorge Acevedo of the Centro de Estudios del Cuaternario de Fuego-Patagonia y Antártica in Punta Arenas, Chile, and colleagues write in the July Polar Biology. When 29 tried to get her pup back, 12 got in front of the pup and made threatening gestures toward 29. And poor 29 could not get her pup back.
The pup, meanwhile, sniffed 12’s back, flank and head. And he suckled from her. Over the next few days, scientists observed that the pup responded to both 12 and 29 when they called. That suggests that the pup had imprinted on both — they were both mom.
Over the next couple of months, 12 continued to make threatening gestures to 29 whenever she approached the pup. But when 12 wasn’t around, 29 was able to feed the young seal. And that was good for the growing male; he gained weight faster and got fatter than other male pups being studied at that time.
Whether there were long-term benefits for this seal in having two moms isn’t known; he was never spotted again. And the researchers never saw another case of fur seal pupnapping.
Acevedo and his colleagues think that this is a case of “misguided parental care,” in which 12 made a mistake in pup recognition in that first day after giving birth to the stillborn pup. But the reason behind the behavior could also be as simple as No. 12 trying to fulfill a desire to be a mom.