Drones Reveal Secret Social Lives and Allomaternal Bonding in Japan’s Narrow-Ridged Finless Porpoises

Kindai University study reveals that narrow-ridged finless porpoises use allomaternal care, with infants swimming alongside unrelated adults in Japan's Ise Bay.

By: AXL Media

Published: Mar 9, 2026, 12:02 PM EDT

Source: The information in this article was sourced from Kindai University

Challenging the Solitary Paradigm of Marine Mammals

For decades, zoologists classified the narrow-ridged finless porpoise as a largely solitary species, contrasting sharply with the highly gregarious pods of dolphins and whales. However, new research published in Mammal Study on October 21, 2025, suggests that the social life of these porpoises is far more nuanced. A team from Kindai University and Mie University documented infant porpoises in Ise Bay engaging in complex interactions with multiple adults. This behavior, known as allomaternal care, involves non-parental adults participating in the rearing or accompaniment of young. According to Associate Professor Mai Sakai, these findings cast doubt on the traditional view of the species and indicate that solitary and social behaviors likely coexist within their population.

Drone Technology Provides a New Perspective

The research team utilized consumer-grade drones to monitor porpoise activity over a 34-day period in 2023, providing a non-invasive view of natural behaviors. By tracking "infant plus two adult" sets, the scientists were able to definitively prove that young porpoises interact with adults who are not their mothers. According to the study, infants were observed approaching, separating from, and parallel swimming with these non-maternal adults. The use of aerial technology allowed for a continuous observation of social dynamics that are often invisible from the surface or boat-based surveys, confirming that these interactions occur with a high frequency in the waters of Ise Bay.

The Mechanics of Parallel Swimming

A key observation of the study was the specific positioning of infants during parallel swimming sessions with non-maternal adults. In every recorded instance, the infant positioned itself on the lateral side of the adult. Researchers believe this behavior serves a functional purpose by reducing water resistance, allowing the smaller infant to maintain a high pace with minimal physical effort. According to the data, this suggests that infants may seek out nearby adults not just for social bonding, but for the practical aerodynamic benefits that make swimming less taxing. This "drafting" behavior highlights a sophisticated level of instinctual cooperation between unrelated individuals.