The manufacture and use of tools, while widespread in terrestrial animals1, has been less frequently reported in marine taxa2. In cetaceans, clear examples of tool use are largely restricted to foraging contexts, with no reports of cetaceans fashioning tools by modifying objects. Here, we report evidence of the widespread manufacture and use of allogrooming tools in a population of resident killer whales (Orcinus orca ater).
In many aquatic taxa, formation traveling can reduce the energetic expenditure of locomotion by exploiting the vorticity trails shed by neighbors or through drafting. Cetaceans, especially odontocetes, often swim in groups; nevertheless, the possibility that whales gain energetic benefits from swimming in formation remains poorly studied, apart from mother-calf pairs. Between June and September in 2019 and 2021, we recorded aerial videos of Southern Resident killer whales (Orcinus orca) in the Salish Sea (USA) travelling in groups. We estimated whale tailbeat and breathing frequencies as proxies of the relative energetic costs of swimming, and tested the effect of swimming speed, relative positioning (e.g., leaders, whales in the middle of groups, or followers), sex and estimated size on these observed proxies. Our results reveal a complex relationship between physical characteristics, relative positioning, and energetic proxies. Intervals between respiration lasted longer in large-sized trailing individuals, but the overall breathing frequency was similar for all whales regardless of their position. The tailbeat frequency was mainly associated to whale sex, size, and swimming speed; in addition, tailbeat frequency showed a decreasing trend as the number of individuals in the formation increased. We found moderate evidence that position-based energetic effects may be present in the formation swimming of killer whales, and it is likely that additional factors such as social ties and hierarchies, play a key role in determining individual positioning in travelling groups. Swimming in formation has been extensively studied in fish and other aquatic animals and has been documented to provide energetic advantages. Our understanding of the potential energetic benefits of wild cetacean formation swimming has been constrained by the difficulties of studying the movement of whale groups from traditional observation platforms. In recent years, non-invasive observations of cetaceans using unoccupied aerial systems have significantly improved the observation of these species in the wild, providing an exciting opportunity to better understand their behaviors and habits. Our results show a tendency for formation swimming to affect two energetic proxies (tailbeat frequency and the duration of underwater intervals between surfacing events). The results of this study set the stage for further research to identify the multiple determinants affecting killer whale formation swimming which go beyond purely energetic advantages, e.g. social relationships.
Southern Resident killer whales (SRKW, Orcinus orca) are a small, endangered population of fish-eating killer whales that inhabit coastal and inland waters of the western United States and British Columbia. SRKW have been in decline since 1995, with food availability, vessel disturbance, and pollutants proposed as drivers of their decline. We used 17 years of sightings data from the SRKW core summer habitat in the Salish Sea to examine trends in presence of SRKW, and how these trends may be related to the availability of a key food source, Fraser River-origin Chinook salmon. We found that SRKW occupancy has declined by more than 75%, in step with reduced average catch per unit effort (CPUE) of Fraser River Chinook salmon. J pod was present in the core summer habitat most often, followed by K and L pods. All three pods demonstrated declines in visitation to the core summer habitat from 2004 to 2020, and presence of SRKW was significantly related to annual average Fraser Chinook CPUE. Our findings suggest that declining Fraser River Chinook returns may be reaching a point where SRKW cannot reliably meet their energetic needs, driving them to forage in areas outside of their traditional core summer habitat.
Photographic identification catalogs of individual killer whales (Orcinus orca) over time provide a tool for remote health assessment. We retrospectively examined digital photographs of Southern Resident killer whales in the Salish Sea to characterize skin changes and to determine if they could be an indicator of individual, pod, or population health. Using photographs collected from 2004 through 2016 from 18,697 individual whale sightings, we identified six lesions (cephalopod, erosions, gray patches, gray targets, orange on gray, and pinpoint black discoloration). Of 141 whales that were alive at some point during the study, 99% had photographic evidence of skin lesions. Using a multivariate model including age, sex, pod, and matriline across time, the point prevalence of the two most prevalent lesions, gray patches and gray targets, varied between pods and between years and showed small differences between stage classes. Despite minor differences, we document a strong increase in point prevalence of both lesion types in all three pods from 2004 through 2016. The health significance of this is not clear, but the possible relationship between these lesions and decreasing body condition and immunocompetence in an endangered, non-recovering population is a concern. Understanding the etiology and pathogenesis of these lesions is important to better understand the health significance of these skin changes that are increasing in prevalence.
The ultimate payoff of behaviours depends not only on their direct impact on an individual, but also on the impact on their relatives. Local relatedness—the average relatedness of an individual to their social environment—therefore has profound effects on social and life history evolution. Recent work has begun to show that local relatedness has the potential to change systematically over an individual’s lifetime, a process called kinship dynamics. However, it is unclear how general these kinship dynamics are, whether they are predictable in real systems and their effects on behaviour and life history evolution. In this study, we combine modelling with data from real systems to explore the extent and impact of kinship dynamics. We use data from seven group-living mammals with diverse social and mating systems to demonstrate not only that kinship dynamics occur in animal systems, but also that the direction and magnitude of kinship dynamics can be accurately predicted using a simple model. We use a theoretical model to demonstrate that kinship dynamics can profoundly affect lifetime patterns of behaviour and can drive sex differences in helping and harming behaviour across the lifespan in social species. Taken together, this work demonstrates that kinship dynamics are likely to be a fundamental dimension of social evolution, especially when considering age-linked changes and sex differences in behaviour and life history. A model of how local relatedness changes with age fits empirical patterns from seven group-living mammal species and reveals that patterns differ between the sexes and the potential behavioural consequences of these changes.
