Year-Round Dive Characteristics of Male Beluga Whales From the Eastern Beaufort Sea Population Indicate Seasonal Shifts in Foraging Strategies

Dive behavior represents multiple ecological functions for marine mammals, but our understanding of dive characteristics is typically limited by the resolution or longevity of tagging studies. Knowledge on the time-depth structures of dives can provide insight into the behaviors represented by vertical movements; furthering our understanding of the ecological importance of habitats occupied, seasonal shifts in activity, and the energetic consequences of targeting prey at a given depth. Given our incomplete understanding of Eastern Beaufort Sea (EBS) beluga whale behavior over an annual cycle, we aimed to characterize dives made by belugas, with a focus on analyzing shifts in foraging strategies. Objectives were to (i) characterize and classify the range of beluga-specific dive types over an annual cycle, (ii) propose dive functions based on optimal foraging theory, physiology, and association with environmental variables, and (iii) identify whether belugas undergo seasonal shifts in the frequency of dives associated with variable foraging strategies. Satellite-linked time-depth-recorders (TDRs) were attached to 13 male belugas from the EBS population in 2018 and 2019, and depth data were collected in time series at a 75 s sampling interval. Tags collected data for between 13 and 357 days, including three tags which collected data across all months. A total of 90,211 dives were identified and characterized by twelve time and depth metrics and classified into eight dive types using a Gaussian mixed modeling and hierarchical clustering analysis approach. Dive structures identify various seasonal behaviors and indicate year-round foraging. Shallower and more frequent diving during winter in the Bering Sea indicate foraging may be energetically cheaper, but less rewarding than deeper diving during summer in the Beaufort Sea and Arctic Archipelago, which frequently exceeded the aerobic dive limit previously calculated for this population. Structure, frequency and association with environmental variables supports the use of other dives in recovery, transiting, and navigating through sea ice. The current study provides the first comprehensive description of the year-round dive structures of any beluga population, providing baseline information to allow improved characterization and to monitor how this population may respond to environmental change and increasing anthropogenic stressors.

Automated VHF-Radio Telemetry Reveals Resource-Driven Site Utilisation Patterns in a Small-Bodied, Highly Mobile Bird (Erythrura Gouldiae)

BackgroundInformation on site utilisation and movement is essential for managing species' resource requirements. Collecting these data requires frequent location sampling of multiple individuals, which can be challenging for small-bodied animals due to the often-large size of animal-borne satellite-based telemetry devices. We show how coded VHF-radio nano-transmitters and an array of passive receivers to collect location data at sufficient frequency and accuracy can be utilised to test whether the highly mobile and small-bodied Gouldian finch adheres to optimal foraging theory within a landscape of high spatiotemporal heterogeneity.MethodsCoded VHF-radio nano-transmitters (0.23 g wt.) were attached to 38 Gouldian finches (Erythrura gouldiae; < 12g bd. wt). Tagged birds were then detected by an array of 6 passive VHF-radio receivers (~ 530 m detection range) spread over 120 km2. We tracked the tagged birds during two sessions corresponding with high and low abundance of their primary food resource (Sorghum spp. seed). The mean and total duration that an individual spent within any receiver detection field (residence time) were used as dependants in a generalised linear mixed model approach within a Bayesian framework to assess the influence of tracking session, life stage, receiver site, and release site. Network analysis revealed the importance of specific areas for the finches within the receiver array using the proportional time a bird spent within any receiver's detection field and the movement between adjacent detection fields. ResultsThe daily mean and total duration that a tagged individual spent within a receiver detection field decreased by ~50% between periods of high and low seed availability, while the extent of movements across the landscape increased with a decline in seed resources. These data support the hypothesis that the Gouldian finch adheres to optimal foraging theory to survive periods of food scarcity. ConclusionsThe data collected via passive telemetry technology support the hypothesis that the Gouldian finch adheres to optimal foraging theory and uses alternative behavioural strategies to survive periods of food scarcity. Specifically, we found that Gouldian finches reduced the time spent foraging within a patch, increased the frequency of transit flights among patches, and expanded the size of their activity space as grass resources declined.

Réflexions sur la proportion du lapin de garenne (Oryctolagus cuniculus) dans le régime alimentaire des chasseurs-cueilleurs autour du Dernier Maximum Glaciaire en Ibérie

Hoy en día el conejo europeo (Oryctolagus cuniculus) es considerado invasivo en varios países. Sin embargo, los motivos del inicio de la explotación de este lagomorfo en el Paleolítico Superior en la península ibérica son objeto de un intenso debate sin que todavía exista un consenso general sobre las causas que explican su introducción en la dieta de los cazadores-recolectores ibéricos. En este artículo, primero presentamos cómo su caza comenzó antes del Último Máximo Glacial (UMG), aumentando durante este periodo. Luego evaluamos las principales hipótesis del Modelo de Amplitud de Dieta (Diet Breadth Model), desarrollado a partir de la Teoría del Forrajeo Óptimo (Optimal Foraging Theory). Este modelo (a veces implícito) es el origen de algunas de estas hipótesis, pero hasta ahora nunca se había aplicado de forma concreta al UMG en la península ibérica. En consecuencia, nosotros lo hemos hecho y los resultados obtenidos no parecen apoyar las hipótesis que defienden una intensificación de la explotación del medio ambiente. Sugerimos que el aprovechamiento de este taxon en torno al UMG en Iberia podría explicarse más bien por el uso de redes entre varias personas. [fr] Bien qu’aujourd’hui le lapin de garenne (Oryctolagus cuniculus) soit considéré comme une espèce invasive dans plusieurs pays, il fait l’objet d’un débat intense quant aux raisons du début de son exploitation durant le Paléolithique supérieur dans la péninsule ibérique. Cependant, aucun consensus général n’existe afin d’expliquer les causes de son introduction dans la diète des chasseurs-cueilleurs ibériens. Ici, nous présentons d’abord que sa chasse a débuté avant le Dernier Maximum Glaciaire (DMG) et qu’elle s’est accrue durant cette période. Ensuite, nous évaluons les principales hypothèses soutenues à partir du Modèle Classique du Régime Alimentaire (MCRA; Diet Breadth Model) issu de la Théorie de l’Approvisionnement Optimal (TAO; Optimal Foraging Theory). Bien que ce modèle soit à l’origine (parfois implicitement) de plusieurs de ces hypothèses, il n’a jamais été appliqué concrètement au DMG dans la péninsule. Nous avons alors appliqué ce modèle et les résultats obtenus ne semblent pas appuyer les hypothèses soutenant une intensification de l’exploitation de l’environnement. Plutôt, nous suggérons que l’utilisation de filets par plusieurs personnes pourrait expliquer l’exploitation de ce taxon autour du DMG en Ibérie.

How gathering wild rice under human-mediated drought stress could have inadvertently paved the way to Asian rice incipient domestication and cultivation

In eastern China, on the southern end of the Yangtze Valley, early Holocene hunter-gatherers were foraging various plants, including wild rice – Oryza rufipogon Griff. – an aquatic and perennial plant which is the wild progenitor of domesticated rice. According to optimal foraging theory, these foragers should have tried to enhance the efficiency of harvesting wild rice seeds by draining water around the plants before seeds ripened and shattered. This proto-cultivation practice led to unintended consequences given that wild rice responds to drought stress owing to its phenotypic plasticity. Plant and panicle architectures were modified with transitions to more compact and erect tillers and to a closed panicle shape. They provide incentives to early foragers for intensifying their proto-cultivation practices and so could have also triggered initial cultivation of rice. They also triggered incipient domestication of rice, starting by the transition to selfing. According to this narrative, it is even possible that rice incipient domestication preceded cultivation.

Adaptive foraging behaviour increases vulnerability to climate change

Adaptative foraging behavior should promote species coexistence and biodiversity under climate change as predators are expected to maximize their energy intake, according to principles of optimal foraging theory. We test these assumptions using a dataset comprising 22,185 stomach contents of fish species across functional groups, feeding strategies, and prey availability in the environment over 12 years. Our results show that foraging shifts from trait-dependent prey selectivity to density dependence in warmer and more productive environments. This behavioral change leads to lower consumption efficiency as species shift away from their optimal trophic niche, undermining species persistence and biodiversity. By integrating this adaptive foraging behavior into dynamic models, our study reveals higher risk profiles for ecosystems under global warming.

Optimal Foraging

This chapter is a refresher on the prey model of classic optimal foraging theory through the lens of this book. I build on the multi-species functional response, the selection ideas, and the parameter breakdown presented in the preceding chapters to argue for how optimal foraging might arise. I rederive the models and suggest that optimal foraging theory may still be relevant to understanding predator–prey interactions, in particular in the context of multi-species functional responses. I also address the possibility that predators mostly have broad diets because they experience low prey abundances most of the time in nature.

Uncertainty drives deviations in normative foraging decision strategies

Nearly all animals forage to acquire energy for survival through efficient search and resource harvesting. Patch exploitation is a canonical foraging behaviour, but there is a need for more tractable and understandable mathematical models describing how foragers deal with uncertainty. To provide such a treatment, we develop a normative theory of patch foraging decisions, proposing mechanisms by which foraging behaviours emerge in the face of uncertainty. Our model foragers statistically and sequentially infer patch resource yields using Bayesian updating based on their resource encounter history. A decision to leave a patch is triggered when the certainty of the patch type or the estimated yield of the patch falls below a threshold. The time scale over which uncertainty in resource availability persists strongly impacts behavioural variables like patch residence times and decision rules determining patch departures. When patch depletion is slow, as in habitat selection, departures are characterized by a reduction of uncertainty, suggesting that the forager resides in a low-yielding patch. Uncertainty leads patch-exploiting foragers to overharvest (underharvest) patches with initially low (high) resource yields in comparison with predictions of the marginal value theorem. These results extend optimal foraging theory and motivate a variety of behavioural experiments investigating patch foraging behaviour.

Be different to be better: the effect of personality on optimal foraging with incomplete knowledge

Many animal populations include a diversity of personalities, and these personalities are often linked to foraging strategy. However, it is not always clear why populations should evolve to have this diversity. Indeed, optimal foraging theory typically seeks out a single optimal strategy for individuals in a population. So why do we, in fact, see a variety of strategies existing in a single population? Here, we aim to provide insight into this conundrum by modelling the particular case of foraging seabirds, that forage on patchy prey. These seabirds have only partial knowledge of their environment: they do not know exactly where the next patch will emerge, but they may have some understanding of which locations are more likely to lead to patch emergence than others. Many existing optimal foraging studies assume either complete knowledge (e.g. Marginal Value Theorem) or no knowledge (e.g. Lévy Flight Hypothesis), but here we construct a new modelling approach which incorporates partial knowledge. In our model, different foraging strategies are favoured by different birds along the bold-shy personality continuum, so we can assess the optimality of a personality type. We show that it is optimal to be shy (resp. bold) when living in a population of bold (resp. shy) birds. This observation gives a plausible mechanism behind the emergence of diverse personalities. We also show that environmental degradation is likely to favour shyer birds and cause a decrease in diversity of personality over time.