Robin William Baird

While coastal delphinid sociality has been extensively investigated across the globe, little is known about the social structure of odontocetes in the open ocean. The rough‐toothed dolphin ( Steno bredanensis ) is a globally distributed oceanic dolphin occurring in tropical and warm‐temperate waters. Around the main Hawaiian Islands, two demographically distinct populations have been identified: one off Kauaʻi and Niʻihau, the other off Hawaiʻi Island. We investigated differences in network structure and association patterns between these populations using photo‐identification data collected from 2002–2020. Social network analysis revealed that the Kauaʻi–Niʻihau population was more subdivided into distinct social clusters (i.e., had higher modularity: 0.58 vs. 0.47) and less densely interconnected (i.e., lower network density: 0.07 vs. 0.12) than the Hawaiʻi Island population. Mean association strength within clusters was higher off Hawaiʻi Island (0.31) than off Kauaʻi–Niʻihau (0.22). Social connections off Hawaiʻi Island also relied more strongly on a smaller number of individuals that linked clusters together. We suggest that differences in population density and habitat extent may contribute to differences in social network structure. Although low re‐sighting rates limited our ability to characterize either population comprehensively, applying identical methods allowed us to identify relative differences in network structure between them.

Marine mammals navigate their environment both horizontally and vertically, adding an additional layer of complexity to understanding their behavior and developing effective conservation strategies. Here, we use data from 14 tagged common bottlenose dolphins ( Tursiops truncatus ) from Hawai'i to explore how their diving behavior varies in response to temporal and demographic variables. Overall mean dive depth (for dives ≥ 50 m) was 206 m (max = 896 m), and duration was 5.9 min (max = 13.6 min). However, individual variation was considerable and explained most of the variation in dive depths and durations. Dive rates varied between diel periods, with rates at night more than double those during the day. Dive depths and durations also varied between diel periods, with animals generally conducting their deepest and longest dives during dusk and their shortest and shallowest dives at night. Regular dives to or close to the seafloor occurred in depths of up to 800 m, but animals spent the majority of their time in the top 50 m of the water column. These findings represent the first baseline data on diving behavior for this species in Hawai'i and will be critical in evaluating potential impacts stemming from planned marine infrastructure development.

Compared to their well‐studied coastal temperate counterparts, killer whales ( Orcinus orca ) in tropical‐subtropical and oceanic areas are under‐documented. We used sighting, photo‐identification, and acoustic data of killer whales in the central tropical Pacific (CTP), collected from multiple platforms between 2002 and 2023, to assess their temporal and spatial distribution, group dynamics and behavior, movements, pigmentation and dorsal fin morphology, and vocalizations. Killer whales were rarely encountered but occur year‐round in the CTP, primarily in waters deeper than 1000 m. Photo‐identification of 113 individuals included multi‐year resightings of individuals off the main Hawaiian Islands but found no matches to eastern tropical Pacific catalogs. CTP killer whales share characteristics with other tropical‐subtropical killer whale populations including pigmentation and morphology, small group sizes (range: 1–12, Mdn = 5), and diverse prey choices (e.g., other cetaceans, bony fishes, and sharks). Acoustic recordings, collected during shipboard sightings, were dominated by echolocation clicks and high‐frequency modulated whistles and provide the first detailed characterization of CTP killer whale vocalizations. This is the most expansive study of CTP killer whales to date, and it underscores the importance of continued collaboration between research groups and the local community in order to better understand rarely sighted species.

Spatial and social behaviours in animals are intertwined, yet the causal direction of this feedback—and how it varies across scales—remains largely unresolved. Using long-term data from false killer whales ( Pseudorca crassidens ) in the main Hawaiian Islands, we developed and applied a scale-explicit analytical framework to test how social reliance and resource ephemerality govern top-down versus bottom-up processes linking movement and sociality. Movements, association networks, genetic relatedness, and isotopic niches reveal that strong social bonds drive bottom-up emergence of short-term intra-group movements, while ephemeral and likely island-associated prey landscapes impose top-down constraints on inter-group dynamics across scales. These complementary processes generate persistent, fine-scale fidelity within some groups and relatively well-differentiated feeding niches among them. Our findings highlight a general mechanism by which life-history strategies and environmental stochasticity jointly determine the scale and direction of feedback between space use and sociality—shaping population structure and connectivity in mobile social predators.

Epigenetic aging models hold great promise for enhancing many aspects of wildlife research and management. However, their utility is limited by the need to train models using known‐aged animals, which are rare among wildlife species. We present a novel approach to developing methylation‐based age prediction models that enables us to train models using samples from individuals whose chronological age is estimated with uncertainty based on photo‐identification catalogue data. Our approach incorporates this uncertainty into model training by representing the age of each individual with a probability distribution rather than a point estimate. We similarly represent the methylation profiles of individuals as binomial distributions and produce a distribution of predicted age for each sample that reflects the uncertainty in both its age and methylation profile. We compared age models trained using a wide range of parameterisations, training data sets and analytical methods to determine how well they predicted the catalogue‐based age estimates. The resulting model has a median absolute error of 1.70 years, outperforming many published clocks trained with known‐age samples. This approach significantly expands the range of species for which accurate methylation‐based age models can be developed, particularly those of conservation concern where known‐age samples are limited. By producing distributions of predicted age, it also enables researchers to accurately communicate the uncertainty in their age estimates to subsequent data users.

Diving is one of the most important behaviors undertaken by marine mammals. Pilot whales (Globicephala spp.) are oceanic dolphins that regularly forage at extreme depths (∼600–1000 m) and maintain body sizes similar to beaked whales. They are also listed as data deficient, with little known about their population dynamics. To help fill this knowledge gap, we estimated their energetic demands through a combination of multiple data streams (e.g. unoccupied aerial systems photogrammetry, high-resolution accelerometry tag data, stomach content analysis and long-duration dive data from satellite tags) from short-finned pilot whales (Globicephala macrorhynchus) in Hawaiian waters. We estimated and compared pilot whale field metabolic rates from breathing frequency against a more granular cost of transport method developed from morphometrics and swimming kinematics, finding that these methods gave similar estimates of energetic expenditure during foraging dives. We then combined expenditure and intake estimates into an exploratory model of daily net energetic balance. Using an estimate of prey size derived from squid beaks collected from a stranded animal, we found that an average of 142±59.8 squid day−1 (52,000±21,800 squid year−1) is enough for an average adult short-finned pilot whale to reach a neutral net energetic balance. This species has an estimated population abundance of ∼8000 individuals in Hawaiian waters, suggesting that the population as a whole would require 416±175 million squid (at an average of 559±126 kJ squid−1) or approximately 88,000±37,000 tonnes of squid annually, assuming similar energetic requirements for each animal.

Age is important for studying population dynamics, but it is difficult to obtain reasonably accurate age estimates and associated uncertainty of free‐ranging individuals, especially for cetaceans. We developed a protocol for deriving probabilistic age estimates using information commonly curated in marine mammal photo‐identification catalogs and applied the approach to 81 biopsy‐sampled and genetically sexed false killer whales ( Pseudorca crassidens ) from the endangered main Hawaiian Islands insular population. The protocol integrates qualitative evidence into a quantitative framework for deriving age estimates and plausible age ranges. Confidence ratings reflecting the strength of available evidence were developed to account for uncertainty. Estimates were then translated to statistical distributions to depict probabilistic age estimates that can be used in further analyses. Age estimates ranged from 3 to 40 years (minimum: 1–33; maximum: 5–65) and were strongly influenced by the estimated age when first seen and length of sighting history. Sensitivity analyses show that population‐level age distribution estimates are robust to age class misclassifications and lack of auxiliary information, including sex. This protocol may provide a guide for aging individuals of some species from photo‐identification catalogs and for which other aging methods from biological samples are not yet feasible or available.

Studies of cetacean diving behavior in multiple locations in different ocean basins allow for an assessment of variability within and among populations. We examine foraging dive behaviors of goose‐beaked whales ( Ziphius cavirostris ) and dense‐beaked whales ( Mesoplodon densirostris ) using data from 132 tagged whales in seven locations in the Pacific and Atlantic Oceans and the Mediterranean Sea. Acoustic recording tags are used to identify foraging dives by the presence of echolocation. For other tag types, foraging dives are identified based on maximum dive depth. Five parameters are used to characterize foraging dives: maximum dive depth, foraging dive duration, dive cycle duration, and the mean and standard deviation of echolocation depths. We find that differences among dives within one tagged individual are typically larger than the differences among individuals or among locations, and that differences among individuals are typically similar in magnitude to differences among locations. Regression is used to estimate the mean and standard deviation of echolocation depths from maximum dive depth for dives without acoustic data. Composite values of foraging dive parameters (and standard deviations) are estimated as the average of all study locations.