Traditionally, mammalian infants rely heavily on maternal care immediately post-birth, as the mother typically provides nourishment, protection, and social learning opportunities essential for survival. In various social mammals, allomaternal care—where individuals other than the mother assist in offspring care—plays an important role, especially in group-living species. This phenomenon provides benefits such as increased infant survival rates and enhanced reproductive efficiency for the mother. In terrestrial mammals, this behavior often occurs among related females, particularly younger or nulliparous females, who gain maternal experience.

Finless porpoises, as odontocetes (toothed whales), have been assumed to diverge from this pattern, exhibiting pronounced social isolation. Prior to this study, observations suggested their social groups are limited, largely consisting of transient mother-infant pairs or rare cooperative aggregations for feeding or transit. The new findings, led by Associate Professor Mai Sakai of Kindai University’s Marine Mammal Research Laboratory, reveal more complex and flexible social interactions suggesting the presence of allomaternal care in what was thought to be a simple social system.

Using consumer-grade drones, Sakai’s research team conducted aerial behavioral observations over 34 days across multiple months in 2023. The drone technology enabled non-invasive and detailed tracking of finless porpoise movements and interpersonal proximity with unprecedented precision. The criteria for identifying allomaternal behavior involved documenting infants engaged in prolonged parallel swimming—a social swimming behavior—alongside multiple adults that were not the infants’ mothers. The study recorded at least four instances where one infant interacted sequentially with two adults, highlighting a dynamic social environment rather than strict maternal exclusivity.

Parallel swimming, a behavior characterized by coordinated swimming in the same direction at close range, is a significant social indicator among many cetaceans. The investigation found that infants positioned themselves laterally alongside adults during these sessions, a formation theorized to reduce hydrodynamic drag and conserve energy by leveraging the adult’s wake. This suggests that infants not only seek social contact but may also gain biomechanical and energetic advantages through association with adults beyond their mothers, signaling a potential adaptive function of social swimming in this species.

Interestingly, the study noted instances of adults initiating contact with infants, possibly representing allomaternal females gaining experience before their own reproductive events. Although the sex of the interacting adults was not definitively determined, the implications are substantial. Such interactions resemble “allosuckling” or handling by young, non-reproductive females witnessed in other social mammals. This behavior may contribute to social learning, infant protection, and the formation of social bonds independent of strict kin relationships.

Despite these occurrences, the proportion of time infants spent swimming parallel to any single adult, other than their mothers, was relatively low—typically less than 40%. This contrasts with observations in other delphinid species, where mother-infant pairs display more persistent and exclusive affiliations. Dr. Sakai interprets this as evidence of a comparatively weaker mother-calf bond in narrow-ridged finless porpoises, possibly reflecting an evolutionary adaptation to their coastal, highly turbid habitats where prolonged maternal dependence may be less feasible or necessary.

The implications of these findings extend well beyond behavioral ecology, touching on conservation strategies for this vulnerable species. Previously, the presumed solitary nature of finless porpoises complicated rehabilitation efforts following calf orphaning or abandonment. Recognizing that non-maternal adults engage socially and may provide care opens doors for more effective interventions, utilizing allomaternal individuals in captive or semi-wild rehabilitation programs. This fundamentally changes the framework for managing juvenile survival in conservation contexts.

Moreover, the successful deployment of cost-effective drone platforms highlights a non-invasive, scalable methodology for observing elusive marine mammals in complex environments. Traditional boat-based surveys face limitations due to disturbance risks and visibility constraints in turbid waters. Drones afford closer and longer-duration monitoring while minimizing stress-related bias in behavior, setting a precedent for future ethological and conservation-oriented studies in marine biology.

These discoveries prompt us to reconsider the social ecology of species traditionally thought to be solitary or exhibit rudimentary social structures. The narrow-ridged finless porpoise exemplifies a transitional social strategy—individuals capable of both solitary and socially flexible behaviors, tailored to environmental and developmental demands. Further research is necessary to dissect the cost-benefit dynamics for all involved parties: mothers, calves, and non-maternal adults. Such studies are critical for understanding the evolution of sociality in marine mammals and guiding adaptive management approaches.

Summarizing, the nuanced social interactions comprising changing partners during parallel swimming among neonatal and adult finless porpoises challenge entrenched notions of species’ solitude. This emerging social complexity has profound implications for ecological theory, conservation practice, and technological advancement in wildlife research methodologies. As this area of inquiry progresses, it is anticipated that broader patterns of social adaptability in other “solitary” species will come to light, refining our comprehension of mammalian social evolution in aquatic environments.

In reflecting on these findings, Associate Professor Mai Sakai emphasized the potential developmental and social benefits of allomaternal behaviors, positing these interactions as compensatory mechanisms for the modest maternal bonds in the species. Continued longitudinal studies leveraging drone technology and detailed behavioral analysis will be indispensable in uncovering the full spectrum and ecological significance of these interactions, ultimately informing both academic understanding and practical conservation efforts for the narrow-ridged finless porpoise.

Subject of Research: Animals
Article Title: Observations of Changing Partners During Parallel Swimming Behavior Between Neonatal and Adult Finless Porpoises (Neophocaena asiaeorientalis) in Ise Bay, Japan
News Publication Date: 21-Oct-2025
Web References: https://doi.org/10.3106/ms2024-0055
References: Sakai, M., Noro, S., Yagi, G., Terada, T., et al. (2025). Observations of Changing Partners During Parallel Swimming Behavior Between Neonatal and Adult Finless Porpoises (Neophocaena asiaeorientalis) in Ise Bay, Japan. Mammal Study. DOI: 10.3106/ms2024-0055
Image Credits: Assistant Professor Genfu Yagi from Mie University, Japan

Keywords: Ethology, Organismal biology, Ecology, Marine biology, Conservation biology, Endangered species, Mammals, Wildlife management, Life sciences

Harbour porpoises, commonly inhabiting Scottish coastal waters, are notoriously difficult to study due to their small size, rapid movements, and brief surfacing intervals. Traditional observation methods, such as boat or land-based watching, often fail to capture their full behavioral repertoire. The advent of drone technology has provided researchers with a novel aerial perspective, enabling continuous and detailed observation while minimizing disturbance to the animals. This vantage point has unveiled complex social interactions that had eluded scientists for decades.

The research was spearheaded by Sophie Ariadne Francine Smith from UHI Shetland as part of her doctoral studies, during which she also became a licensed drone pilot. The project was catalyzed by an observation from Karen Hall of NatureScot, Sophie’s PhD supervisor, who noted unusual surface splashing that hinted at mating activity. Recognizing the limitations of existing monitoring methods, the team deployed drones to capture this ephemeral behavior, which typically lasts only a few seconds per surfacing event.

Analyzing over 79 minutes of high-quality footage from diverse coastal locations including Gulberwick Bay, South Nesting Bay, Mousa Sound, and Quendale Bay, the scientists identified gatherings of harbour porpoises in numbers far exceeding prior expectations. While previous reports tended to record porpoises in pairs or triplets, the drones documented assemblies of up to 26 individuals simultaneously. This finding suggests that harbour porpoise social structures are considerably more complex and dynamic than previously understood.

The researchers observed two distinct types of sexual behaviors. The first involved males swiftly approaching females in what appeared to be copulation attempts. These vigorous interactions often culminated in individual porpoises breaking the surface amidst conspicuous splashing—a phenomenon initially captured by onshore observers. The second behavior comprised a specific form of display where males would roll to reveal their undersides to females, presumably as part of a courtship ritual or sexual signaling mechanism.

This detailed characterization of porpoise mating behavior is significant not only for ethologists but also for conservationists aiming to protect these marine mammals. Harbour porpoises, despite their relative abundance locally, remain vulnerable due to their elusive nature and the increasing anthropogenic pressures in their habitats. By understanding when and where they congregate, and the social contexts driving these gatherings, conservation management can be finely tuned to mitigate risks such as bycatch, noise pollution, and habitat disruption.

The contributions of this study extend beyond mere behavioral cataloging; they emphasize the intersection of ecology, technology, and community involvement. Collaborating closely with Shetland residents and incorporating local ecological knowledge allowed the research team to optimize their data collection within the narrow and often challenging weather windows characteristic of the region. This synergy between science and community exemplifies how participatory approaches can enhance the effectiveness of marine spatial planning and species conservation.

Dr. Lauren McWhinnie from Heriot-Watt University, a co-supervisor of the research, highlighted the broader implications of these findings. Although North Sea harbour porpoise populations are considered relatively stable, fine-scale regional data such as this are critical for assessing local threats and guiding strategic interventions. These efforts align with the designation of Shetland and Fair Isle as an Important Marine Mammal Area (IMMA) in 2024, underscoring the international commitment to safeguard key cetacean habitats.

Moreover, Dr. Rachel Shucksmith of UHI Shetland emphasized the innovative aspect of drone deployment in marine mammal research. Despite the logistical constraints posed by Shetland’s often inclement weather, the technological advancements utilized in this project allow for unprecedented behavioral observation. This methodological innovation paves the way for future studies across other challenging marine environments, promising richer insights into cetacean ecology and behavior globally.

The funding for this research was provided by the NERC Scottish Universities Partnership for Environmental Research (SUPER) Doctoral Training Partnership and supplemented by the National Lottery Heritage Fund. Such support underscores the growing recognition of marine mammal research as a vital component of environmental stewardship. The diverse expertise involved, including supervisors from the Scottish Association for Marine Science (SAMS) and NatureScot, as well as collaborative input from multiple scientists, reflects the interdisciplinary nature required to advance our understanding of these enigmatic creatures.

In essence, this research not only documents the social and reproductive behaviors of harbour porpoises in unprecedented detail but also demonstrates the transformative potential of integrating emerging technologies with traditional ecological inquiry. As climate change and human activity continue to alter marine ecosystems, such detailed baseline studies become ever more crucial. This work sets a new standard for marine mammal behavioral research and conservation strategy, offering hope that we can protect these vital species through informed, adaptive management.

The culmination of this study was published in the Journal of the Marine Biological Association of the United Kingdom on March 5, 2026, under the title “Sexual interactions and unexpected group sizes in harbour porpoises.” This seminal article invites further research and discussion, driving a paradigm shift in how scientists and policymakers approach the study and safeguarding of harbour porpoises and similar marine mammals worldwide.

Subject of Research: Animals
Article Title: Sexual interactions and unexpected group sizes in harbour porpoises
News Publication Date: 5-Mar-2026
Image Credits: McCaffery, Shucksmith and Smith
Keywords: Marine biology, harbour porpoises, cetacean behavior, drone technology, mating behavior, Shetland waters, conservation, Important Marine Mammal Area (IMMA), marine mammal ecology