Seal mothers care for deceased pups, exhibiting unique mammalian behavior in Antarctic predator species

A new paper by University of Rhode Island post-doctoral researchers Emily Sperou and Renato Borras-Chavez in the journal Polar Biology discusses a unique phenomenon observed in a reclusive Antarctic animal: postmortem attentive behavior,  or PAB, in the solitary leopard seal. The two are members of URI’s CEAL Lab in the Department of Natural Resources Science.

Their paper documents a previously undescribed form of maternal behavior in leopard seals, and one of the longest documented PAB cases recorded in any mammal. PAB is a rare occurrence where an individual gives attention or care to a dead individual.

Renato Borras-Chavez and Emily Sperou are members of URI’s CEAL Lab, which studies leopard seals and other apex predators. (URI Photo/Alex Garcia Ruiz)

Sperou and Borras-Chavez’s team observed mother leopard seals carrying and attending to their deceased pups for more than 20 days, with one female exhibiting the behavior across multiple years. The team’s study explores potential hypotheses for why pups may be dying and why mothers appear unable to let go, situating these observations within the broader context of behaviors that are typically associated with species such as orcas, chimpanzees, and elephants.

Unique species, shared behavior

One female seal displayed PAB for at least 20 days, the longest documented case in pinnipeds and among the longest for any mammal. (URI Photo/Emily Sperou)

Postmortem attentive behavior is a rare form of care-giving in which individuals show attachment, distress, or curiosity toward deceased species-mates, most often between mothers and offspring. Mammalian maternal behavior encompasses diverse behaviors and adaptations to ensure the survival and development of offspring. Such behavior illustrates maternal investment: the time, energy, and resources animal mothers allocate to their offspring.

In remote marine environments, studying such behavior is particularly challenging. Yet, understanding maternal behavior in this challenging landscape can help explain how ecological pressures shape evolutionary adaptations and wildlife bonding.

Postmortem attentive behavior has been documented in several terrestrial mammals, including primates, African elephants, dingos, hogs, and giraffes. PAB is less frequently reported in marine mammals, likely due to the challenges of observing these animals within aquatic environments. In comparison to cetaceans (whales, dolphins and porpoises), only six PAB cases have been documented in pinnipeds (seals, sea lions, and walruses).

Spotting behavior

One way the team is tracking the leopard seal is by its namesake spots. Borras-Chavez and Sperou use the seals’ unique hide pattern to track and follow individual seals throughout their lives.

After scanning thousands of images to verify what they were seeing, the implications of the observed behavior quickly gained researchers’ attention.

“This was a unique behavior to witness,” Sperou says, noting they decided to write their observations up when they realized what they were seeing was more than a one-time occurrence.

“It’s actually a maladaptive trait,” Sperou says. “This behavior is not beneficial for the animal. We hope to learn why the seals are exhibiting this behavior.”

Borras-Chavez and Sperou verified their observations with tour operators and confirmed verification of the individual seals using catalogs maintained for study in the region. In collaboration with Baylor University computer scientists Jorge Yero and Pablo Rivas, Borras-Chavez recently helped develop an algorithm, which they’ll start to use via the organization Happywhale, to replace the analog catalog they’ve been using to identify leopard seals from their spot patterns. The computer program will save time on the cumbersome scanning and reviewing of thousands of images and could also be used with other animals.

Sperou suggests that the seal’s behavior could be because they are mammals, same as humans, with the same physiology and hormones. Even though the behavior is energy intensive, it could be a behavioral response to the cascade of hormones produced after giving birth.

“Those hormones could still be circulating in the mother,” Sperou says. “Perhaps she can’t let go because of the hormones. This is such a complex and hard species to study; I learn something new every expedition.”

Sperou hopes to learn more about the animal’s reproductive patterns and is starting to pursue additional ways of studying the animal. Using museum samples of leopard seals from all over the world — including Paris, Oslo, and Patagonia — they can learn even more about the life history of this unique species.

Both say the local CONAF monitoring agency (National Forestry Corporation of Chile) has been essential in studying leopard seals in the region. Borras-Chavez credits the park rangers who assist the team in studying the elusive animal within this remote region, sharing their own observations on the ground and water.

“It takes a whole village to do this kind of work,” Sperou adds.

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