Drone Footage Captures Rare Moments of Finless Porpoises Caring for Others’ Calves

Flightless porpoises are generally considered loners. They are usually seen alone or in single pairs, most often a mother swimming with her young, leading researchers to assume that the animals have relatively simple social lives.

But images taken by drones in Japan call this idea into question. The researchers observed what appeared to be allomaternal interactions, with small porpoises approaching and swimming alongside adults who were not their mothers. The behavior, reported in the newspaper Mammal studysuggests that the species may be more social than previously thought.

“Allomaternal behaviors may be beneficial to newborns in the development of social relationships and/or as a complement to the weaker mother-calf relationships that are typical of this vulnerable developmental stage,” lead author Mai Sakai said in a press release.

Learn more: Like kindergarten friends, male dolphins who maintain friendships can live longer

Allomaternal care in finless porpoises

In many social mammals, infants are not solely cared for by their mothers.

Other adults, often young females without young, sometimes handle, guard, or swim with the infants. This behavior, known as allomaternal care, has been observed in animals ranging from primates to dolphins.

For young people, these interactions can provide protection or help them learn social skills. For adults, this may offer practice before raising their own offspring. And for mothers, it can give them more time to forage.

Allomaternal behavior has been documented in many toothed whales, including dolphins and porpoises. But the finless porpoise with narrow crests remains an exception. As these animals rarely form large groups, it was assumed that such cooperative behavior was unlikely.

Monitoring of finless porpoise calves

To study how these porpoises interact, Sakai and his colleagues used consumer drones to observe the animals in Ise Bay, Japan.

For 34 days between February and July 2023, the team recorded aerial images of porpoises swimming near the surface. The objective was to identify cases in which an infant interacted with more than one adult during a single observation.

These times could indicate that the infant was spending time with a non-maternal adult. In four cases, researchers observed groups consisting of an infant and two adults.

During many of these interactions, the infant swam parallel to an adult – a behavior researchers call parallel swimming. In all cases, the infant remained alongside the adult.

This position can help the calf keep pace while using less energy because the adult’s movement in the water reduces resistance.

Less lonely than we thought

Most of the time, calves approached nearby adults rather than the other way around, perhaps seeking protection or an easier ride in the water. However, in two cases, the adults moved towards the young.

These adults could be young females without offspring, although the drone images did not allow researchers to confirm their sex.

The calves also spent less than 40% of their time swimming alongside a single adult – far less than the time calves typically spend alongside their mothers in other dolphin species. This trend suggests that finless porpoises may form looser mother-calf bonds than many other toothed whales.

Despite this, the interactions challenge the long-held idea that the species lives primarily solitary. The study also shows how simple drone technology can help track marine animals without disturbing them.

This discovery could also be important for conservation. If other adults sometimes interact with the calves, these relationships could help the young orphans survive.

“To understand allomaternal behavior in species with simple social structures, future studies need to evaluate the cost-benefit relationship for mothers, calves, and non-maternal adults,” Sakai concluded.

Learn more: Just like humans, groups of dolphins have complex social structures

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