Flexible Foraging Research Articles

Carbon and nitrogen sources in tropical coastal lagoon food webs under variable hydrological conditions

Whilst the impact of continental and marine nutrient sources on the ecological functioning of coastal food webs is well investigated in temperate regions, tropical ecosystems remain less well understood, in particular coastal lagoons. In this study, the sources of carbon and nitrogen in a coastal lagoon system in the southeast of Madagascar are traced using stable isotopes of carbon (δ13C) and nitrogen (δ15N). Three interconnected coastal lagoons with different degree of river influence and eutrophication are investigated. Their food webs are assessed with respect to spatial and seasonal (wet and dry seasons) variations in lagoon water conditions, as well as with respect to the sources of nutrients and organic matters. Results show that river input is the main source of NO3−, and that NO3− supply is significantly higher during the wet season. In contrast, NH4+ is produced internally in the lagoon, and concentrations are higher during the dry season. A lower δ13C value observed in particulate organic matter (POM; proxy of phytoplankton) indicates terrestrial-riverine carbon inputs, which generally have low δ13C values. During the dry season, exceptionally high δ15N values of lagoon POM suggest the uptake of newly produced lagoon water NH4+ and/or the 15N enrichment of lagoon POM pool due to mineralization, resulting in 15N enrichment in consumers. Moreover, δ13C and δ15N values of consumers (fishes and invertebrates) reflect predominantly those of lagoon POM and sediment organic matter (SOM), suggesting that consumers primarily depend on lagoon POM and SOM as sources of carbon and nitrogen. The δ15N values in consumers further indicate that some species feed on more than one trophic level, suggesting flexible foraging strategy of consumers as a function of food source availability. This study demonstrates the roles of both river inflow and sediment in supplying carbon and nitrogen to a coastal lagoon food web, documenting the ecological implications of seasonal variations in lagoon hydrological conditions.

Variable foraging and flower probing behaviour of sunbird pollinators of the South African Pelargonium fulgidum

ABSTRACT Whether foraging sunbird pollinators hover or perch, the type of perch used, and the direction of flower probing are generally thought to be determined by matching shapes of decurved bird bills and curved flower tubes, as well as inflorescence architecture. However, few studies have objectively quantified aspects of sunbird foraging behaviour to test predictions based on adaptive trait matching. I investigated sunbird foraging in a population of Pelargonium fulgidum, a species with slightly upcurved flowers borne on upward-oriented peduncles, which grows along the west coast of South Africa. Long-range photographs revealed that Cinyris chalybeus, a sunbird species with a slightly decurved bill, hovers or perches during foraging, and uses both the inflorescence and alternative vegetation structures as perch. Contrary to previous suggestions, both male and female sunbirds probe flowers from either of two alternative directions (sternotribic versus nototribic) in more or less equal proportions, and frequently display flexibility in both foraging behaviour and flower probing direction. Predominant or complete sternotribic and nototribic flower probing were explained by hovering versus use of an inflorescence perch respectively, whereas use of an alternative perch resulted in similar proportions of each mode of flower probing. The number of flowers per visited inflorescence and number and proportion of probed flowers did not vary with foraging behaviour or flower probing direction. Although certain foraging behaviours resulted in predictable flower probing directions, variation in foraging behaviour and the presence of many alternative perches provided by vegetation surrounding P. fulgidum plants resulted in variability in flower probing direction that appears not to affect foraging efficiency. Relatively weak reciprocal curvature of flower tube and sunbird bill, resulting in easy access to nectar from multiple feeding directions, likely facilitates flexible foraging. This study shows that environmental context may facilitate more complex foraging behaviour than that predicted by adaptive trait matching.

Seed Availability and Small Mammal Populations: Insights from Mediterranean Forests

Plant–animal interactions play a crucial role in ecosystem functioning, especially through seed dispersal mechanisms. Understanding how small mammal populations respond to seed availability is essential for ecosystem management and biodiversity conservation, especially in the context of habitat loss and climate change. We conducted a 10-year study in mixed Mediterranean oak–beech forests to investigate the population dynamics of common small mammal species in response to seed availability. Our findings revealed distinct responses among species, influenced by life history traits, foraging behaviour, and diet. Wood mice (Apodemus sylvaticus) showed a rapid population increase with seed availability both in the same year of seed fall and the following year, suggesting a flexible foraging strategy and a dependence on arboreal seed producers. Yellow-necked mice (Apodemus flavicollis) revealed immediate population increases in response to seed availability in the autumn, probably because of their arboreal habits and preference for exploiting seeds prior to maturation. Bank voles (Clethrionomys glareolus) showed responses with population peaks in years following high seed availability, indicating a slower demographic response to resource abundance. Surprisingly, the greater white-toothed shrew (Crocidura russula) responded indirectly to seed availability in Mediterranean forests, suggesting complex interactions with seed-associated invertebrates or dependence on other variables not considered. Our findings highlight the importance of understanding how changes in seed availability influence the population ecology of small mammals, with significant implications for the conservation and management of Mediterranean forest ecosystems in the context of climate change and recurrent droughts. These results emphasise the need to consider species interactions, resource availability, and climate change in the conservation and management of evolving ecosystems.

A trait‐based understanding of the vulnerability of a Paleotropical moth community to predation by a sympatric bat with flexible foraging strategies

Abstract Prey vulnerability across seasons can be predicted by measuring their morphological traits and availability. Although conventional prey–predator dynamics focus on pairs of prey and predator species, the trait‐based approach allows us to draw inferences at the scale of the entire assemblage. Here, we coupled measurable prey traits with their availability in the study area, to identify the vulnerability of a diverse moth assemblage to predation by the lesser false vampire bat (Megaderma spasma) Chiroptera: Megadermatidae, Linneaus 1758, a bat with flexible foraging strategies, in the Western Ghats biodiversity hotspot of India. We analysed the discarded prey remains from several roosts, collected over 3 years, for seasonal patterns in the diet and selective hunting. Through light‐trapping, we collected moth specimens in different seasons and measured the morphological traits likely to affect their vulnerability to predation, such as body size and evasive flight capability. Our results showed that consumed moth prey diversity varies seasonally, with moths belonging to the Hepialidae family being preferred in the wet season. We found that the larger moth species with lower evasive capabilities are more vulnerable to predation. Sphingid and Hepialid moths, among the most abundant in the diet, have the lowest manoeuvrability and the maximum body size, respectively. By assessing vulnerability at the prey assemblage level, our study sets the stage for future research on moth–bat interactions from the diverse and less‐explored Paleotropical communities. In addition, the study reiterates the usefulness of trait‐based approaches to understanding prey–predator dynamics.

Flexible foraging and mating behaviours in an orb weaver

Flexible foraging and mating behaviours in an orb weaver

Flexible foraging behaviour increases predator vulnerability to climate change

Higher temperatures are expected to reduce species coexistence by increasing energetic demands. However, flexible foraging behaviour could balance this effect by allowing predators to target specific prey species to maximize their energy intake, according to principles of optimal foraging theory. Here we test these assumptions using a large dataset comprising 2,487 stomach contents from six fish species with different feeding strategies, sampled across environments with varying prey availability over 12 years in Kiel Bay (Baltic Sea). Our results show that foraging shifts from trait- to density-dependent prey selectivity in warmer and more productive environments. This behavioural change leads to lower consumption efficiency at higher temperature as fish select more abundant but less energetically rewarding prey, thereby undermining species persistence and biodiversity. By integrating this behaviour into dynamic food web models, our study reveals that flexible foraging leads to lower species coexistence and biodiversity in communities under global warming.

Land planarians (Platyhelminthes) also prey on web-building spiders

Although spiders and land planarians constitute diverse groups of terrestrial predators, interactions between them are still unknown. Here, we describe a predatory event of a land planarian (Choeradoplana cf. gladismariae) on a web-building spider (Helvibis longicauda) in the Brazilian Atlantic Forest. The prey was constricted and covered with sticky mucus while remaining on its web trying to protect its egg sac. The event was observed in the middle-end afternoon at ca. 1.80 m height. Our observation broadens the scope of possible natural enemies of web-building spiders and the prey items of land planarians. It also indicates that these organisms can capture and overpower dangerous predatory arthropods, suggesting that even complex three-dimensional sticky webs can be ineffective against the attack of land planarians. Finally, we also show that land planarians can exhibit a flexible foraging strategy, exploiting the environment during the day and at higher heights from the ground. Our observation opens new possibilities involving focal observations and experiments using spiders and land planarians as models in predator-prey research.

The southern cassowary (Casuarius casuarius johnsonii) remains an important disperser of native plants in fragmented rainforest landscapes

AbstractLarge‐bodied frugivores are essential to the ecological function of rainforest communities. The southern cassowary (Casaurius casuarius johnsonii) is the only large frugivore in the tropical rainforests of Australia. Here, we assessed whether cassowaries remain important to native plant seed dispersal in areas where the rainforest is highly fragmented, and exotic fruits are abundant. To do this, we developed a tri‐axial acceleration logger integrated with a motion sensor and VHF radio transmitter. The telemetry device was small enough to be hidden inside a native fruit. The cassowaries ingested it, transported it and defecated it up to 24 h later with the seeds from the fruits they had ingested during the tracking period. The telemetry device was then located by VHF radio and collected with the scat. The distance travelled, activity profile, consumed fruit diversity, and scat energy content were assessed for cassowaries inhabiting regions with different degrees of urbanization. We found that cassowaries inhabiting more urbanized areas consumed the greatest proportion of fruits from exotic plants (~30%) but still incorporated a significant proportion of fruits from native plants in their diet. These individuals existed in higher states of activity and rested less than individuals inhabiting more intact swathes of rainforest, actively moving between urban gardens and the rainforest. The study shows cassowaries have a flexible foraging strategy that has enabled them to persist in rainforest‐fragmented landscapes. They remain a significant disperser of seeds from native plants between rainforest patches, and as such, cassowaries remain essential in maintaining native plant diversity within these fragmented patches.

Seasonal variation in prey preference, diet partitioning and niche breadth in a rich large carnivore guild

AbstractLarge carnivore community structure is affected by direct and indirect interactions between intra‐guild members. Co‐existence between different species within a carnivore guild may occur through diet, habitat or temporal partitioning. Since carnivore species are highly dependent on availability and accessibility of prey, diet partitioning is potentially one of the most important mechanisms in allowing carnivores to co‐exist. Intra‐guild interactions may vary over time as carnivore prey preference and diet overlap can change due to seasonal changes in resource availability. We conducted scat analysis to compare the seasonal changes in prey preference, diet partitioning and niche breadth of four large carnivore species, namely leopard Panthera pardus, spotted hyena Crocuta crocuta, brown hyena Parahyaena brunnea and wild dog Lycaon pictus in central Tuli, Botswana. Large carnivores in central Tuli display a high dietary overlap, with spotted hyena and brown hyena displaying almost complete dietary overlap and the other carnivore species displaying slightly lower but still significant dietary overlap. Dietary niche breadth for both hyena species was high possibly due to their flexible foraging strategies, including scavenging, while leopard and wild dog showed a relatively low niche breadth, suggesting a more specialised diet. High dietary overlap in central Tuli is possibly explained by the high abundance of prey species in the area thereby reducing competition pressure between carnivore species. Our research highlights the need to assess the influence of diet partitioning in structuring large carnivore communities across multiple study sites, by demonstrating that in prey rich environments, the need for diet partitioning by carnivores to avoid competition may be limited.

Feeding Ecology of Odontaster validus under Different Environmental Conditions in the West Antarctic Peninsula.

To study how Odontaster validus can influence the spatial structure of Antarctic benthic communities and how they respond to disturbance, it is necessary to assess potential dietary shifts in different habitats. We investigated the diets of O. validus from Maxwell Bay and South Bay in the West Antarctic Peninsula. A multifaceted approach was applied including in situ observations of cardiac stomach everted contents, isotopic niche, and trophic diversity metrics. Results confirm the flexible foraging strategy of this species under markedly different environmental conditions, suggesting plasticity in resource use. The data also showed evidence of isotopic niche expansion, high δ15N values, and Nacella concinna as a common food item for individuals inhabiting a site with low seasonal sea ice (Ardley Cove), which could have significant ecological implications such as new trophic linkages within the Antarctic benthic community. These results highlight the importance of considering trophic changes of key species to their environment as multiple ecological factors can vary as a function of climatic conditions.

Short- and long-term modulation of forager motivation by colony state in bumble bees

The question of how animals make decisions has been intensely studied by ethologists, behavioural ecologists, psychologists and neuroscientists alike. Foraging bumble bees are an excellent system to study decision making because, as eusocial insects, foragers are solely focused on the task of collecting food for the colony. Bumble bees are generalist foragers of ephemeral resources that do not store food long term and are thus expected to show flexible adjustments in foraging motivation in response to stored food. However, their feeding behaviour at resources as a function of stored food has not been explored. Here, we present results demonstrating that bumble bees ( Bombus impatiens ) show flexible adjustments in foraging motivation in response to colony food stores across different timescales. First, bumble bees showed decreased foraging motivation as the colony accumulated food over the course of a day. Second, bees that developed in colonies with full food stores showed persistently lower motivation than bees developing in colonies with impoverished food stores even days after those food stores were removed. We further demonstrate that this persistent low motivation may be explained by the lower amount of abdominal lipids in nutrient-depleted colonies. Our results provide evidence for a mechanism that may mediate the social control of individual foraging motivation, an important step in the evolution of eusociality. • We examined bumble bee feeding behaviour at resources as a function of stored food. • We tested bees from provisioned and unprovisioned colonies. • Bees showed flexible foraging based on colony food stores across timescales. • Bees from provisioned colonies showed lower foraging motivation. • This low foraging motivation may be explained by lower abdominal lipid levels.

Prey selection of polar bears in Foxe Basin, NU, Canada: evidence of dietary flexibility in a specialized predator

AbstractEcological flexibility of a species reflects its ability to cope with environmental change. Although polar bears (Ursus maritimus) are experiencing changes in foraging opportunities due to sea ice loss, regional prey availability and environmental conditions will influence the rate and severity of these effects. We examined changes in polar bear diet and the influence of sea ice characteristics in Foxe Basin over an 18-year period. We combined previous fatty acid data from bears harvested from 1999 to 2003 (n = 82) with additional data from 2010 to 2018 (n = 397). Polar bear diets were diverse; however, ringed seal (Pusa hispida) was the primary prey throughout the sample period. Prey contribution varied temporally and spatially, and by intrinsic factors, while the frequency of prey in diets varied over time suggesting that diet estimates reflect the variability in available prey. Bowhead whale (Balaena mysticetus), although still a minor dietary component, has more than doubled in frequency of occurrence in diets in recent years in association with increased scavenging opportunities. Higher dietary levels of beluga whale (Delphinapterus leucas) and harbour seal (Phoca vitulina) were linked to later breakup date suggesting heavier ice conditions may promote access to both prey species. The flexible foraging strategies of bears in Foxe Basin may help mitigate their vulnerability to changes in prey distribution and habitat conditions. Our results provide insights into the importance of alternative and supplemental food sources for polar bears during phenological changes in ice conditions that will likely have consequences to Arctic community structure as warming continues.

Differential reliance on aquatic prey subsidies influences mercury exposure in riparian arachnids and songbirds.

Cross‐ecosystem subsidies move substantial amounts of nutrients between ecosystems. Emergent aquatic insects are a particularly important prey source for riparian songbirds but may also move aquatic contaminants, such as mercury (Hg), to riparian food webs. While many studies focus on species that eat primarily emergent aquatic insects, we instead study riparian songbirds with flexible foraging strategies, exploiting both aquatic and terrestrial prey sources. The goal in this study is to trace reliance on aquatic prey sources and correlate it to Hg concentrations in common riparian arachnids (Families Tetragnathidae, Opiliones, and Salticidae) and songbirds (Common Yellowthroat Geothlypis trichas, Spotted Towhee Pipilo maculatus, Swainson's Thrush Catharus ustulatus, Song Sparrow Melospiza melodia, and Yellow Warbler Setophaga petechia). We used stable isotopes of δ13C and δ15N and Bayesian mixing models in MixSIAR to determine the reliance of riparian predators on aquatic prey sources. Using mixed effects models, we found that arachnid families varied in their reliance on aquatic prey sources. While songbird species varied in their reliance on aquatic prey sources, songbirds sampled earlier in the season consistently relied more on aquatic prey sources than those sampled later in the season. For both arachnids and songbirds, we found a positive correlation between the amount of the aquatic prey source in their diet and their Hg concentrations. While the seasonal pulse of aquatic prey to terrestrial ecosystems is an important source of nutrients to riparian species, our results show that aquatic prey sources are linked with higher Hg exposure. For songbirds, reliance on aquatic prey sources early in the breeding season (and subsequent higher Hg exposure) coincides with timing of egg laying and development, both of which may be impacted by Hg exposure.

Both short and long distance migrants use energy-minimizing migration strategies in North American herring gulls

BackgroundRecent studies have proposed that birds migrating short distances migrate at an overall slower pace, minimizing energy expenditure, while birds migrating long distances minimize time spent on migration to cope with seasonal changes in environmental conditions.MethodsWe evaluated variability in the migration strategies of Herring Gulls (Larus argentatus), a generalist species with flexible foraging and flight behaviour. We tracked one population of long distance migrants and three populations of short distance migrants, and compared the directness of their migration routes, their overall migration speed, their travel speed, and their use of stopovers.ResultsOur research revealed that Herring Gulls breeding in the eastern Arctic migrate long distances to spend the winter in the Gulf of Mexico, traveling more than four times farther than gulls from Atlantic Canada during autumn migration. While all populations used indirect routes, the long distance migrants were the least direct. We found that regardless of the distance the population traveled, Herring Gulls migrated at a slower overall migration speed than predicted by Optimal Migration Theory, but the long distance migrants had higher speeds on travel days. While long distance migrants used more stopover days overall, relative to the distance travelled all four populations used a similar number of stopover days.ConclusionsWhen taken in context with other studies, we expect that the migration strategies of flexible generalist species like Herring Gulls may be more influenced by habitat and food resources than migration distance.

Flexible Foraging Response of Wintering Hooded Cranes (Grus monacha) to Food Availability in the Lakes of the Yangtze River Floodplain, China.

Simple SummaryWith increasing human activity, bird habitats are being degraded and lost. In order to survive, birds have to adapt to the deteriorating environment. In this study, we surveyed the availability of food resources to Hooded Cranes in a degraded wetland. We found that cranes adopted flexible foraging strategies in response to the abundance and availability of different food resources in mosaic wetland landscapes at different periods during winter. The results also showed that the deeper the food was buried, the more time the cranes spent, and foraging frequency and foraging success rate were based on food abundance. It provided an evidence basis for the protection and management of waterbirds, especially Hooded Cranes.Wetlands are disappearing or degrading at an unprecedented rate due to the increase in human encroachment and disturbance, eventually leading to habitat loss for waterbirds, which is the primary cause of the decline in the Hooded Crane (Grus monacha) population. The Hooded Cranes have to constantly adjust their foraging strategies to survive to cope with this situation. In order to study how cranes respond to food resources in mosaic habitat, we surveyed a total of 420 food quadrats and 736 behavioral samples from three habitats during three wintering periods in Shengjin Lake and Caizi Lake. We measured temporal and between-habitat differences in foraging time budget, foraging frequency, and foraging success rate. Akaike’s information criterion was selected between the models of food abundance and availability. The results indicated that the wintering cranes spent the majority of their time (66.55%) foraging and shifted their foraging behaviors based upon food abundance and availability in different habitats. Our analyses also indicated that cranes were willing to forage more food with poor sediment penetrability in sub-optimal habitats. Foraging time budget was based on the food depth, and the foraging frequency and foraging success rate were based on food abundance. Cranes adopted flexible foraging strategies in response to the alternative food resources in mosaic wetland habitats, as it could mitigate the negative impacts of habitat loss and facilitate survival.

At-sea movements of wedge-tailed shearwaters during and outside the breeding season from four colonies in New Caledonia

The wedge-tailed shearwater (WTS) population of New Caledonia is one of the largest in the world, yet its biology and foraging ecology are poorly known. We studied WTS from 4 colonies in New Caledonia. We examined foraging behaviour and habitats using GPS receivers and light sensors during and outside the breeding season, respectively, and compared our findings with those from other WTS populations worldwide. During breeding, New Caledonian WTS alternated short foraging trips close to the colony over the lagoon, or off the reef edge, with longer trips over distant, deep waters. Whereas neighboring colonies overlapped at sea, especially during short trips, there was a clear separation of foraging zones between the pairs of colonies located in the southern versus northwestern parts of New Caledonia. Although WTS actively foraged and commuted to foraging zones during the day, they mainly returned to the colony or rested at night, indicating that they feed mainly during the day. Active foraging did not take place in more productive areas, suggesting that it may instead be related to the presence of sub-surface predators. Outside the breeding season, birds from 3 colonies had similar trans-equatorial migratory behaviour. All left New Caledonia at the same time of the year with a fast, northeasterly movement and wintered over deep waters in the same sector of the northwestern tropical Pacific Ocean. At overwintering sites, they spent most of their non-foraging time presumably sitting on the water, especially at night, making a slow westward movement before returning to New Caledonia. WTS from New Caledonia forage over warm, oligotrophic deep waters throughout their life cycle, and the species appears to have a flexible foraging strategy adapted to the various environmental conditions encountered across its wide tropical range.

Predator-informed looming stimulus experiments reveal how large filter feeding whales capture highly maneuverable forage fish

The unique engulfment filtration strategy of microphagous rorqual whales has evolved relatively recently (<5 Ma) and exploits extreme predator/prey size ratios to overcome the maneuverability advantages of swarms of small prey, such as krill. Forage fish, in contrast, have been engaged in evolutionary arms races with their predators for more than 100 million years and have performance capabilities that suggest they should easily evade whale-sized predators, yet they are regularly hunted by some species of rorqual whales. To explore this phenomenon, we determined, in a laboratory setting, when individual anchovies initiated escape from virtually approaching whales, then used these results along with in situ humpback whale attack data to model how predator speed and engulfment timing affected capture rates. Anchovies were found to respond to approaching visual looming stimuli at expansion rates that give ample chance to escape from a sea lion-sized predator, but humpback whales could capture as much as 30-60% of a school at once because the increase in their apparent (visual) size does not cross their prey's response threshold until after rapid jaw expansion. Humpback whales are, thus, incentivized to delay engulfment until they are very close to a prey school, even if this results in higher hydrodynamic drag. This potential exaptation of a microphagous filter feeding strategy for fish foraging enables humpback whales to achieve 7× the energetic efficiency (per lunge) of krill foraging, allowing for flexible foraging strategies that may underlie their ecological success in fluctuating oceanic conditions.

Does upper limb robusticity and bilateral asymmetry support subsistence intensification at Roonka, South Australia?

During the Holocene, what is now the state of South Australia experienced a shift to a drier climate with more frequent droughts c. 4 ka. The ‘intensification model’ in Australian archaeology proposes that Aboriginal people adopted subsistence strategies that exploited resources with high processing costs, while the ‘risk minimization’ model posits that people adopted more flexible foraging strategies. The purpose of this study is to determine whether human groups in South Australia demonstrate evidence for intensification or risk minimisation in response to declining patch quality by examining bone properties of the upper limb in a Holocene skeletal sample from Roonka. Cross-sectional geometry of the humeri and radii was used to examine temporal trends of diaphyseal rigidity and bilateral asymmetry in both sexes. Women show a significant temporal increase in robusticity and rigidity of the upper limbs; men have similar measurements between time periods. Neither sex exhibits a difference in bilateral asymmetry of the humeri and radii over time. These results support risk minimisation at Roonka. In the late Holocene, it is possible that men hunted large game, while women had mixed foraging strategies that involved hunting small game, digging tubers, processing seeds, and collecting shellfish to mitigate high resource variance.

Trophic Patterns of Bighead Carp and Silver Carp Follow the Seasonality of Resource Availability

The influence of seasonality of the aquatic environment on food web has been notoriously understudied in empirical ecology. In this study, we focus on seasonal changes in one key attribute of a food web, the trophic level. We determine whether seasonal variations of fish trophic levels could be indicated by the change in food resources. Silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) were used to explore the responses of trophic levels of the filter-feeding fish to seasonal variations of food resources. Combined stable isotopic analysis and dietary analysis revealed that filter-feeding fish tended to have a higher trophic level in spring (May) and autumn (September and October). This may result from the abundant density of food resources (zooplankton and phytoplankton) and fish flexible foraging strategy, as we predicted that the trophic level follows the seasonality of food availability. Pearson’ correlation analysis and a structural equation model showed that seasonal variation of total phosphorus and water temperature could indirectly affect trophic levels of silver carp and bighead carp by mediating the abundance of phytoplankton and zooplankton directly and indirectly along the food chain. According to these findings, the seasonal variation of food resources could be an important indicator of the temporal dynamics of the food web trophic pattern in freshwater ecosystems.

High individual flexibility in the foraging behavior of a marine predator, the common murre

The foraging ecology of breeding seabirds is largely influenced by prey availability and energy demands related to reproduction which, in combination with other factors, can affect resource specialization in space and time. In this study, we combined GPS tracking, dive behavior, and stable isotope ratios of carbon and nitrogen to examine behavioral and dietary flexibility within individuals in a breeding pursuit-diving seabird, the common murre (Uria aalge), on the northeast Newfoundland coast. We examined individual flexibility over 2 years (2016, 2017) during which the timing of arrival and availability of their primary prey, capelin (Mallotus villosus), varied. In both years, we found high within-individual variation in foraging trip and dive characteristics, coupled with low spatial overlap of foraging trips both within and among individuals, indicative of flexible behavior. Concurrently, the isotopic niche of breeding common murres showed a higher degree of dietary consistency, evidenced by similar amounts of variation within and among individuals in stable isotope ratios (δ13C, δ15N). Dietary reconstruction revealed that the proportion of different prey types in the diet varied across individuals, suggesting a degree of dietary flexibility. When capelin (prey) availability was low (in 2017), foraging trips were longer and farther from the colony, maximum dive duration decreased, and the proportion of capelin in the diet decreased. Behavioral flexibility, however, remained similar across both years, regardless of prey availability. Our results suggest that common murres can tolerate and respond to fluctuations in prey availability through flexible foraging strategies. Increased foraging distances during low capelin availability suggest increased energetic costs, and thus, an energetic threshold may be reached above which lower prey availability cannot be tolerated.