Foraging behavior links sea ice to breeding success in Antarctic penguins

Delay in Adélie penguin nest occupation restricts parental investment in nest construction and reduces reproductive output

Reproductive success is an important demographic parameter that can be driven by environmental and behavioural factors operating on various spatio-temporal scales. As seabirds breed on land and forage in the ocean, processes occurring in both environments can influence their reproductive success. At various locations around East Antarctica, Adélie penguins' (Pygoscelis adeliae) reproductive success has been negatively linked to extensive sea-ice. In contrast, our study site in the Windmill Islands has limited fast ice present during the breeding season, allowing us to examine drivers of reproductive success under vastly different marine environmental conditions. Here, we examined the reproductive success of 450 Adélie penguin nests over a 10-year period using images obtained from remotely operated cameras. We analysed nest survival in relation to marine and climatic factors, environmental conditions at the camera site and immediately around the nest, and behavioural attributes reflecting parental investment and phenological timing. Our key result was a strong positive association between nest structure and chick survival, particularly when ground moisture and snow cover around the nest were high. Earlier nesting birds were more likely to build bigger nests, although it is unclear whether this is due to more time available to build nests or whether early arrival and high-quality nests are complementary traits. This intrinsic activity is likely to become more important if future predictions of increased snowfall in this region manifest.

Climate and human stressors on global penguin hotspots: Current assessments for future conservation

As charismatic and iconic species, penguins can act as "ambassadors" or flagship species to promote the conservation of marine habitats in the Southern Hemisphere. Unfortunately, there is a lack of reliable, comprehensive, and systematic analysis aimed at compiling spatially explicit assessments of the multiple impacts that the world's 18 species of penguin are facing. We provide such an assessment by combining the available penguin occurrence information from Global Biodiversity Information Facility (>800,000 occurrences) with three main stressors: climate-driven environmental changes at sea, industrial fisheries, and human disturbances on land. Our analyses provide a quantitative assessment of how these impacts are unevenly distributed spatially within species' distribution ranges. Consequently, contrasting pressures are expected among species, and populations within species. The areas coinciding with the greatest impacts for penguins are the coast of Perú, the Patagonian Shelf, the Benguela upwelling region, and the Australian and New Zealand coasts. When weighting these potential stressors with species-specific vulnerabilities, Humboldt (Spheniscus humboldti), African (Spheniscus demersus), and Chinstrap penguin (Pygoscelis antarcticus) emerge as the species under the most pressure. Our approach explicitly differentiates between climate and human stressors, since the more achievable management of local anthropogenic stressors (e.g., fisheries and land-based threats) may provide a suitable means for facilitating cumulative impacts on penguins, especially where they may remain resilient to global processes such as climate change. Moreover, our study highlights some poorly represented species such as the Northern Rockhopper (Eudyptes moseleyi), Snares (Eudyptes robustus), and Erect-crested penguin (Eudyptes sclateri) that need internationally coordinated efforts for data acquisition and data sharing to understand their spatial distribution properly.

Global warming and arctic terns: Estimating climate change impacts on the world's longest migration

Climate change is one of the top three global threats to seabirds, particularly species that visit polar regions. Arctic terns migrate between both polar regions annually and rely on productive marine areas to forage, on sea ice for rest and foraging, and prevailing winds during flight. Here, we report 21st-century trends in environmental variables affecting arctic terns at key locations along their Atlantic/Indian Ocean migratory flyway during the non-breeding seasons, identified through tracking data. End-of-century climate change projections were derived from Earth System Models and multi-model means calculated in two Shared Socioeconomic Pathways: 'middle-of-the-road' and 'fossil-fuelled development' scenarios. Declines in North Atlantic primary production emerge as a major impact to arctic terns likely to affect their foraging during the 21st century under a 'fossil-fuelled development' scenario. Minimal changes are, however, projected at three other key regions visited by arctic terns (Benguela Upwelling, Subantarctic Indian Ocean and the Southern Ocean). Southern Ocean sea ice extent is likely to decline, but the magnitude of change and potential impacts on tern survival are uncertain. Small changes (<1 m s-1 ) in winds are projected in both scenarios, but with minimal likely impacts on migration routes and duration. However, Southern Ocean westerlies are likely to strengthen and contract closer to the continent, which may require arctic terns to shift routes or flight strategies. Overall, we find minor effects of climate change on the migration of arctic terns, with the exception of poorer foraging in the North Atlantic. However, given that arctic terns travel over huge spatial scales and live for decades, they integrate minor changes in conditions along their migration routes such that the sum effect may be greater than the parts. Meeting carbon emission targets is vital to slow these end-of-century climatic changes and minimise extinction risk for a suite of polar species.

Effects of Sea-Ice Persistence on the Diet of Adélie Penguin (Pygoscelis adeliae) Chicks and the Trophic Differences between Chicks and Adults in the Ross Sea, Antarctica

In Antarctica, prey availability for the mesopredator Adélie penguin, Pygoscelis adeliae, depends on sea-ice dynamics. By affecting cycles of sea-ice formation and melt, climate change could thus affect penguin diet and recruitment. In the light of climate change, this raises concerns about the fate of this dominant endemic species, which plays a key role in the Antarctic food web. However, few quantitative studies measuring the effects of sea-ice persistence on the diet of penguin chicks have yet been conducted. The purpose of this study was to fill this gap by comparing penguin diets across four penguin colonies in the Ross Sea and evaluating latitudinal and interannual variation linked to different sea-ice persistence. Diet was evaluated by analysing the δ¹³C and δ¹⁵N values of penguin guano, and sea-ice persistence by means of satellite images. Isotopic values indicate that penguins consumed more krill in colonies with longer sea-ice persistence. In these colonies, the δ¹³C values of chicks were lower and closer to the pelagic chain than those of adults, suggesting that the latter apparently catch prey inshore for self-feeding and offshore for their chicks. The results indicate that sea-ice persistence is among the principal factors that influence the spatiotemporal variability of the penguins' diet.

Biologging and Biotelemetry: Tools for Understanding the Lives and Environments of Marine Animals

Addressing important questions in animal ecology, physiology, and environmental science often requires in situ information from wild animals. This difficulty is being overcome by biologging and biotelemetry, or the use of miniaturized animal-borne sensors. Although early studies recorded only simple parameters of animal movement, advanced devices and analytical methods can now provide rich information on individual and group behavior, internal states, and the surrounding environment of free-ranging animals, especially those in marine systems. We summarize the history of technologies used to track marine animals. We then identify seven major research categories of marine biologging and biotelemetry and explain significant achievements, as well as future opportunities. Big data approaches via international collaborations will be key to tackling global environmental issues (e.g., climate change impacts), and curiosity about the secret lives of marine animals will also remain a major driver of biologging and biotelemetry studies.

The role of individual variability on the predictive performance of machine learning applied to large bio-logging datasets

Animal-borne tagging (bio-logging) generates large and complex datasets. In particular, accelerometer tags, which provide information on behaviour and energy expenditure of wild animals, produce high-resolution multi-dimensional data, and can be challenging to analyse. We tested the performance of commonly used artificial intelligence tools on datasets of increasing volume and dimensionality. By collecting bio-logging data across several sampling seasons, datasets are inherently characterized by inter-individual variability. Such information should be considered when predicting behaviour. We integrated both unsupervised and supervised machine learning approaches to predict behaviours in two penguin species. The classified behaviours obtained from the unsupervised approach Expectation Maximisation were used to train the supervised approach Random Forest. We assessed agreement between the approaches, the performance of Random Forest on unknown data and the implications for the calculation of energy expenditure. Consideration of behavioural variability resulted in high agreement (> 80%) in behavioural classifications and minimal differences in energy expenditure estimates. However, some outliers with < 70% of agreement, highlighted how behaviours characterized by signal similarity are confused. We advise the broad bio-logging community, approaching these large datasets, to be cautious when upscaling predictions, as this might lead to less accurate estimates of behaviour and energy expenditure.

Predicting foraging dive outcomes in chinstrap penguins using biologging and animal-borne cameras

Direct observation of foraging behavior is not always possible, especially for marine species that hunt underwater. However, biologging and tracking devices have provided detailed information about how various species use their habitat. From these indirect observations, researchers have inferred behaviors to address a variety of research questions, including the definition of ecological niches. In this study, we deployed video cameras with GPS and time-depth recorders on 16 chinstrap penguins (Pygoscelis antarcticus) during the brood phase of the 2018–2019 breeding season on Signy (South Orkney Islands). More than 57 h of footage covering 770 dives were scrutinized by two observers. The outcome of each dive was classified as either no krill encounter, individual krill or krill swarm encounter and the number of prey items caught per dive was estimated. Other variables derived from the logging devices or from the environment were used to train a machine-learning algorithm to predict the outcome of each dive. Our results show that despite some limitations, the data collected from the footage was reliable. We also demonstrate that it was possible to accurately predict the outcome of each dive from dive and horizontal movement variables in a manner that has not been used for penguins previously. For example, our models show that a fast dive ascent rate and a high density of dives are good indicators of krill and especially of swarm encounter. Finally, we discuss how video footage can help build accurate habitat models to provide wider knowledge about predator behavior or prey distribution.

Molecular Diet Analysis of Adélie Penguins (Pygoscelis adeliae) in the Ross Sea Using Fecal DNA

Simple Summary

The diet of Adélie penguins, Pygoscelis adeliae, in the Ross Sea was studied applying quantitative polymerase chain reaction (qPCR) protocols to their feces. Two krill species (Euphausia superba and Euphausia crystallorophias) and notothenioid fish (mainly Pleuragramma antarctica and Pagothenia borchgrevinki) were among the most abundant components of the diet. The composition of the two krill species and notothenioid fish was found to be strongly related to the geographic characteristics of the Ross Sea.

Abstract

The diet of Adélie penguins, Pygoscelis adeliae, is a useful indicator in understanding the ecological conditions of their habitats. The diets of Adélie penguins were studied using metabarcoding and quantitative PCR (qPCR) analyses of fecal DNA from seven habitats along the Ross Sea region. Using metabarcoding analysis with dual universal primers (18Sv9 and miniFish), the overall diet composition and detailed information about piscine prey were clearly elucidated. It was found that two krill species (Euphausia superba and Euphausia crystallorophias) and notothenioid fish were the most abundant in the diets of Adélie penguins. Among the notothenioid prey, Pleuragramma antarctica (56.50%) and Pagothenia borchgrevinki (18.21%) were the two most abundant species. qPCR analysis showed a significant geographic difference in the composition of main prey. Penguins inhabiting outbound parts of the Ross Sea (Capes Adare (CA) and Duke of York Island (DY)) mainly preyed on E. superba, without any significant changes in prey composition. By contrast, those inhabiting the inbound parts of the Ross Sea (Edmonson Point (EP) and Inexpressible Island (II)) preyed on E. crystallorophias and notothenioid fish rather than E. superba. Compared with the outbound habitats, prey compositions for penguins inhabiting the inbound regions were significantly different year to year, which was presumably due to the food availability based on the annual environmental and meteorological conditions of the coastal region along with the inbound parts of the Ross Sea.

Mare incognita: Adélie penguins foraging in newly exposed habitat after calving of the Nansen Ice Shelf

Rapid environmental changes can dramatically and durably affect the animal's foraging behavior. In the Ross Sea (Antarctica), calving of the Nansen Ice Shelf in 2016 opened a newly accessible marine area of 214 km². In this study, we examined the foraging behavior of Adélie penguins from the nearby Inexpressible Island in December 2018, by tracking 27 penguins during their at-sea trips using GPS, depth and video loggers. The penguins mainly foraged within 88.2 ± 42.9 km of their colony, for 23.4 ± 6.8 h. Five penguins headed south to the newly exposed habitat along the Nansen Ice Shelf, whereas 22 penguins exploited previously available foraging areas. There was no significant difference in any of the foraging trip or diving parameters between the two penguin groups; however, in the calved region the penguins were diving into shallow areas more often than did the other penguins. These results show that Adélie penguins on Inexpressible Island had explored the newly exposed area after calving. We conclude that the penguins respond to newly available habitat following stochastic environmental events, either through information sharing at the colony, and/or by balancing prey availability per capita across the foraging sites. Considering that this penguin breeding area is under investigation for the establishment of an Antarctic Specially Protected Area (ASPA), the results of this study may provide insights for evaluating the ecological importance of this area and formulating an ASPA management plan for conservation.

Diversity of microbial communities and genes involved in nitrous oxide emissions in Antarctic soils impacted by marine animals as revealed by metagenomics and 100 metagenome-assembled genomes

Antarctic soils generally have low temperatures and limited availability of liquid water and nutrients. However, animals can increase the nutrient availability of ice-free areas by transferring nutrients from marine to terrestrial ecosystems, mainly through their excreta. In this study, we employed shotgun metagenomics and population genome binning techniques to study the diversity of microbial communities in Antarctic soils impacted by marine pinnipeds and birds relative to soils with no evident animal presence. We obtained ~285,000 16S rRNA gene-carrying metagenomic reads representing ~60 phyla and 100 metagenome-assembled genomes (MAGs) representing eight phyla. Only nine of these 100 MAGs represented previously described species, revealing that these soils harbor extensive novel diversity. Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundant phyla in all samples, with Rhodanobacter being one of the most abundant genera in the bird-impacted soils. Further, the relative abundance of genes related to denitrification was at least double in soils impacted by birds than soils without animal influence. These results advance our understanding of the microbial populations and their genes involved in nitrous oxide emissions in ice-free coastal Antarctic soils impacted by marine animals and reveal novel microbial diversity associated with these ecosystems.

Trace elements and stable isotopes in penguin chicks and eggs: A baseline for monitoring the Ross Sea MPA and trophic transfer studies

Multi-tissue trace elements (TEs), C, N concentrations and stable isotopes (δ¹³C, δ¹⁵N) of chick carcasses and eggs of Adélie and Emperor penguins were studied to i) provide reference data before the recent institution of the Ross Sea Marine Protected Area (Antarctica), and ii) provide conversion factors that allow estimating C, N, δ¹³C and δ¹⁵N in edible tissues from non-edible ones, thus improving the use of stable isotopes in contamination and trophic transfer studies. Higher concentrations of As, Cd, Cr, Cu, Hg, Mn and Pb were found in chick carcasses than in eggs, suggesting increasing contamination in recent decades and high toxicity risks for penguin consumers. Isotopic conversion factors highlighted small differences among body tissues and conspecifics. These values suggest that chick carcasses are reliable indicators of the energy pathways underlying the two penguin species, their trophic position in the food web and their exposure to TEs.

Horizontal-vertical movement relationships: Adélie penguins forage continuously throughout provisioning trips

BACKGROUND

Diving marine predators forage in a three-dimensional environment, adjusting their horizontal and vertical movement behaviour in response to environmental conditions and the spatial distribution of prey. Expectations regarding horizontal-vertical movements are derived from optimal foraging theories, however, inconsistent empirical findings across a range of taxa suggests these behavioural assumptions are not universally applicable.

METHODS

Here, we examined how changes in horizontal movement trajectories corresponded with diving behaviour and marine environmental conditions for a ubiquitous Southern Ocean predator, the Adélie penguin. Integrating extensive telemetry-based movement and environmental datasets for chick-rearing Adélie penguins at Béchervaise Island, we tested the relationships between horizontal move persistence (continuous scale indicating low ['resident'] to high ['directed'] movement autocorrelation), vertical dive effort and environmental variables.

RESULTS

Penguins dived continuously over the course of their foraging trips and lower horizontal move persistence corresponded with less intense foraging activity, likely indicative of resting behaviour. This challenges the traditional interpretation of horizontal-vertical movement relationships based on optimal foraging models, which assumes increased residency within an area translates to increased foraging activity. Movement was also influenced by different environmental conditions during the two stages of chick-rearing: guard and crèche. These differences highlight the strong seasonality of foraging habitat for chick-rearing Adélie penguins at Béchervaise Island.

CONCLUSIONS

Our findings advance our understanding of the foraging behaviour for this marine predator and demonstrates the importance of integrating spatial location and behavioural data before inferring habitat use.

Spatial and temporal diet variability of Adélie (Pygoscelis adeliae) and Emperor (Aptenodytes forsteri) Penguin: a multi tissue stable isotope analysis

The Ross Sea, Antarctica, supports large populations of Emperor Penguin (Aptenodytes forsteri) and Adélie Penguin (Pygoscelis adeliae), two key meso-predators that occupy high trophic levels. Despite these species are largely studied, little is known about their diet outside the breeding period. In the present study, we investigated the intra-annual diet of Adélie and Emperor Penguins belonging to five colonies in the Ross Sea through the stable isotope analysis of different tissues (feathers and shell membranes), synthetized in different seasons, and guano that indicates recent diet. Penguin samples and prey (krill and fish) were collected during the Antarctic spring–summer. δ13C and δ15N of tissues and guano indicate spatio-temporal variation in the penguin diet. The krill consumption by Adélie Penguins was lowest in winter except in the northernmost colony, where it was always very high. It peaked in spring and remained prevalent in summer. The greatest krill contribution to Emperor Penguin’s diet occurred in summer. The relative krill and fish consumption by both species changed in relation to the prey availability, which is influenced by seasonal sea ice dynamics, and according to the penguin life cycle phases. The results highlight a strong trophic plasticity in the Adélie Penguin, whose dietary variability has been already recognized, and in the Emperor Penguin, which had not previously reported. Our findings can help understand how these species might react to resource variation due to climate change or anthropogenic overexploitation. Furthermore, data provides useful basis for future comparisons in the Ross Sea MPA and for planning conservation actions.

Too big to study? The biologging approach to understanding the behavioural energetics of ocean giants

Wild animals are under selective pressure to optimise energy budgets; therefore, quantifying energy expenditure, intake and allocation to specific activities is important if we are to understand how animals survive in their environment. One approach toward estimating energy budgets has involved measuring oxygen consumption rates under controlled conditions and constructing allometric relationships across species. However, studying 'giant' marine vertebrates (e.g. pelagic sharks, whales) in this way is logistically difficult or impossible. An alternative approach involves the use of increasingly sophisticated electronic tags that have allowed recordings of behaviour, internal states and the surrounding environment of marine animals. This Review outlines how we could study the energy expenditure and intake of free-living ocean giants using this 'biologging' technology. There are kinematic, physiological and theoretical approaches for estimating energy expenditure, each of which has merits and limitations. Importantly, tag-derived energy proxies can hardly be validated against oxygen consumption rates for giant species. The proxies are thus qualitative, rather than quantitative, estimates of energy expenditure, and have more limited utilities. Despite this limitation, these proxies allow us to study the energetics of ocean giants in their behavioural context, providing insight into how these animals optimise their energy budgets under natural conditions. We also outline how information on energy intake and foraging behaviour can be gained from tag data. These methods are becoming increasingly important owing to the natural and anthropogenic environmental changes faced by ocean giants that can alter their energy budgets, fitness and, ultimately, population sizes.

Emerging evidence of resource limitation in an Antarctic seabird metapopulation after 6 decades of sustained population growth

The influence of resource limitation on spatio-temporal population dynamics is a fundamental theme in ecology and the concepts of carrying capacity, density dependence and population synchrony are central to this theme. The life history characteristics of seabirds, which include use of disjunct patches of breeding habitat, high coloniality during breeding, strong philopatry, and central-place foraging, make this group well suited to studying this paradigm. Here, we investigate whether density-dependent processes are starting to limit population growth in the Adélie penguin metapopulation breeding in the Windmill Islands, East Antarctica, after 6 decades of growth. Our finding that the regional growth rate has slowed in recent decades, and that growth is slowing differentially across local populations as availability of breeding habitat and possibly food resources decrease, supports the notion of density-dependent regulation. Our observation of the first new colonisation of a breeding patch in a half-century of population growth by this highly philopatric species is further evidence for this. Given these emerging patterns of spatio-temporal population dynamics, this metapopulation may be at a point where the rate of change in density-dependent processes and rare events such as colonisations accelerates into the future, potentially providing new insights into spatio-temporal metapopulation dynamics of a long-lived species over a short time-frame. Continued long-term study of populations experiencing these circumstances provides an opportunity to expedite advances in understanding metapopulation processes. Our study highlights the importance of spatial heterogeneity and the mosaic of abiotic and biotic features of landscapes and seascapes in shaping species' metapopulation dynamics.

Adélie penguins foraging consistency and site fidelity are conditioned by breeding status and environmental conditions

There is a growing interest in studying consistency and site fidelity of individuals to assess, respectively, how individual behaviour shapes the population response to environmental changes, and to highlight the critical habitats needed by species. In Antarctica, the foraging activity of central place foragers like Adélie penguins (Pygoscelis adeliae) is constrained by the sea-ice cover during the breeding season. We estimated the population-level repeatability in foraging trip parameters and sea-ice conditions encountered by birds across successive trips over several years, and we examined their foraging site fidelity linked to sea-ice concentrations throughout the chick-rearing season. Penguins' foraging activity was repeatable despite varying annual sea-ice conditions. Birds' site fidelity is constrained by both sea-ice conditions around the colony that limit movements and resources availability, and also behavioural repeatability of individuals driven by phenological constraints. Adélie penguins favoured sea-ice concentrations between 20-30%, as these facilitate access to open water while opening multiple patches for exploration in restricted areas in case of prey depletion. When the sea-ice concentration became greater than 30%, foraging site fidelity decreased and showed higher variability, while it increased again after 60%. Between two trips, the foraging site fidelity remained high when sea-ice concentration changed by ± 10% but showed greater variability when sea-ice concentrations differed on a larger range. In summary, Adélie penguins specialize their foraging behaviour during chick-rearing according to sea-ice conditions to enhance their reproductive success. The balance between being consistent under favourable environmental conditions vs. being flexible under more challenging conditions may be key to improving foraging efficiency and reproductive success to face fast environmental changes.