Testing assumptions of central place foraging theory: a study of Adélie penguins Pygoscelis adeliae in the Ross Sea

We investigated central place foraging (CPF) in the context of optimal foraging theory in Adélie penguins Pygoscelis adeliae of the southern Ross Sea by using satellite tracking and time‐depth recorders to explore foraging at two spatio‐temporal scales: within the day‐to‐day (sub‐mesoscale: single foraging trip, 10s of km²) and the entire breeding season (mesoscale: trips by multiple individuals across the collective foraging area, 100s of km²). Specifically, we examine whether three basic assumptions of the Orians–Pearson CPF model, shown to occur in other CPF species, are met: 1) within a patch, the rate of prey acquisition declines with time spent in that patch; 2) food is distributed in discrete patches and is not available between those patches; and 3) CPF species have knowledge of the potential (or average, at least) feeding rate within their universe of patches, and use this knowledge to determine their foraging strategy when planning or engaging in a foraging trip. We found that prey consumption rates did not decline with time spent in patches, and penguins foraged to some degree most of the time when at sea. Food availability, as measured by foraging dive rate, appeared to be predictable within the same day at the same location, but predictability broke down after 2 d at distances > 10 km away. We conclude that the assumptions of the Orians–Pearson CPF model are not a good fit to the circumstances of Ross Sea penguins, which clearly are central place foragers.     

Spatial segregation between immatures and adults in a pelagic seabird suggests age‐related competition

Individual competitiveness conditions access to resources when they are limited. Immature individuals that are less skilled than adults have to adapt their foraging strategies to survive. Among strategies to reduce competition, spatial segregation has been widely demonstrated. However, the use of spatial segregation by immatures to limit intra‐specific competition with adults has rarely been tested. In this study, we investigated and compared habitat preferences and distributions of free‐ranging immature and breeding adult northern gannets Morus bassanus in order to determine whether they compete for similar habitats during the year, and if this results in a spatial segregation between birds of different age groups. Based on > 66 000 km of aerial surveys conducted in the North‐East Atlantic Ocean during winter and summer 2012, habitats selected by immatures and adult birds were modelled independently, linking gannet density to a set of oceanographic and physiographic predictors. Their large‐scale seasonal distribution was then predicted. We found that gannets displayed a strong season‐dependent competition between immatures and adults, as a consequence of immatures and adults using similar habitats in both summer and winter. During summer, when adults are constrained by reproduction, both groups were spatially highly segregated despite similar habitat preferences (thermal fronts), with youngest individuals selecting habitats out of range of central‐place foragers, highlighting intra‐specific competition. Contrastingly during winter, when reproductive constraints disappear, immature and adult distributions largely overlapped. Our study provides new insights into the role played by age, foraging experience and reproductive constraints on the distribution of marine predators. More specifically, these results highlight in seabirds how the youngest fraction mitigates, through spatial segregation, the competition with experienced adults, and suggest a progressive strategy along the maturation process.     

The influence of thermoregulatory demand on contact crèching behaviour in Adélie Penguin chicks

(1) We tested the hypothesis that contact behaviour in Adélie Penguin (Pygoscelis adeliae) chicks of crèching age is strongly influenced by thermoregulatory demand. (2) Estimated thermoregulatory costs (% minimal metabolic rate) for early crèche stage (1 kg) chicks were much higher (13.4–121.0%) than for late crèche (3 kg) chicks (0–45.1%). The incidence of contact behaviour was high during early crèche, but uncommon during late crèche. (3) Both the percentage of early crèche chicks forming contact groups and the mean number of chicks per group increased significantly as thermoregulatory demand increased. (4) Thermoregulatory costs were significantly higher when late crèche chicks exhibited contact behaviour than when they did not. (5) Contact behaviour in Adélie Penguin chicks therefore appears to perform a thermoregulatory function and probably confers important energy savings in terms of maintaining a favourable daily energy budget and maximum fasting duration.     

Commercial fisheries,inter‐colony competition and sea depth affect foraging location of breeding Scopoli's Shearwaters Calonectris diomedea

The distribution of seabirds at sea is influenced by physical, ecological and anthropogenic factors such as sea depth, prey distribution, intra‐specific competition and commerical fishing activities. We quantified the foraging habitat preferences of Scopoli's Shearwater Calonectris diomedea in the Mediterranean Sea. We analysed habitat preferences in relation to a suite of physical and ecological variables including sea depth, net primary production and distance to other colonies (as a proxy of intra‐specific competition). Since the Mediterranean is heavily impacted by commercial fisheries, we also incorporated the distance to fishing harbours in our analyses as a proxy of the availability of discards which are a potential feeding source for Scopoli's Shearwater. Foraging birds preferred shallower waters and avoided areas close to other colonies, thereby reducing interactions with conspecifics. We also found that long‐distance trips were undertaken to areas close to fishing harbours, suggesting that these represented particularly profitable locations to compensate for the greater travelling costs involved. No differences in foraging between the sexes were recorded. This study improves our understanding of the at‐sea distribution and habitat preference of a seabird inhabiting the over‐exploited Mediterranean Sea. Our results support growing evidence that seabirds exhibit complex relationships with commerical fishing activities, which must be considered when planning conservation programmes.     

Species‐specific foraging strategies and segregation mechanisms of sympatric Antarctic fulmarine petrels throughout the annual cycle

Determining the year‐round distribution and behaviour of birds is necessary for a better understanding of their ecology and foraging strategies. Petrels form an important component of the high‐latitude seabird assemblages in terms of species and individuals. The distribution and foraging ecology of three sympatric fulmarine petrels (Southern Fulmar Fulmarus glacialoides, Cape Petrel Daption capense and Snow Petrel Pagodroma nivea) were studied at Adélie Land, East Antarctica, by combining information from miniaturized saltwater immersion geolocators and stable isotopes from feathers. During the breeding season at a large spatial scale (c. 200 km), the three species overlapped in their foraging areas located in the vicinity of the colonies but were segregated by their diet and trophic level, as indicated by the different chick δ¹⁵N values that increased in the order Cape Petrel < Southern Fulmar < Snow Petrel. During the non‐breeding season, the three fulmarines showed species‐specific migration strategies along a wide latitudinal gradient. Snow Petrels largely remained in ice‐associated Antarctic waters, Southern Fulmars targeted primarily the sub‐Antarctic zone and Cape Petrels migrated further north. Overall, birds spent less time in flight during the non‐breeding period than during the breeding season, with the highest percentage of time spent sitting on the water occurring during the breeding season and at the beginning of the non‐breeding period before migration. This activity pattern, together with the δ¹³C values of most feathers, strongly suggests that moult of the three fulmarine petrels occurred at that time in the very productive high Antarctic waters, where birds fed on a combination of crustaceans and fish. The study highlights different segregating mechanisms that allow the coexistence of closely related species, specifically, prey partitioning during the breeding season and spatial segregation at sea during the non‐breeding season.     

Sea ice predicts long‐term trends in Adélie penguin population growth,but not annual fluctuations: Results from a range‐wide multiscale analysis

Understanding the scales at which environmental variability affects populations is critical for projecting population dynamics and species distributions in rapidly changing environments. Here we used a multilevel Bayesian analysis of range‐wide survey data for Adélie penguins to characterize multidecadal and annual effects of sea ice on population growth. We found that mean sea ice concentration at breeding colonies (i.e., “prevailing” environmental conditions) had robust nonlinear effects on multidecadal population trends and explained over 85% of the variance in mean population growth rates among sites. In contrast, despite considerable year‐to‐year fluctuations in abundance at most breeding colonies, annual sea ice fluctuations often explained less than 10% of the temporal variance in population growth rates. Our study provides an understanding of the spatially and temporally dynamic environmental factors that define the range limits of Adélie penguins, further establishing this iconic marine predator as a true sea ice obligate and providing a firm basis for projection under scenarios of future climate change. Yet, given the weak effects of annual sea ice relative to the large unexplained variance in year‐to‐year growth rates, the ability to generate useful short‐term forecasts of Adélie penguin breeding abundance will be extremely limited. Our approach provides a powerful framework for linking short‐ and longer term population processes to environmental conditions that can be applied to any species, facilitating a richer understanding of ecological predictability and sensitivity to global change.     

Examination of fine‐scale spatial‐temporal overlap and segregation between two closely related congeners Gadus morhua and Gadus ogac in coastal Newfoundland

The spatial and temporal movement patterns of sympatric juvenile Atlantic cod Gadus morhua and Greenland cod Gadus ogac were studied using high‐resolution radio‐acoustic positioning in a coastal area of Newfoundland during the summers of 2009 and 2010. A total of 20 fish (10 G. ogac and 10 G. morhua) were equipped with acoustic transmitters and monitored for periods up to 23 days. Most fishes showed high site fidelity with mean residence times of 12·4 (G. morhua) and 14·4 days (G. ogac). A few individuals showed a transient use of the study area, ranging distances up to c. 4 km. Mean daily home ranges [95% kernel utilization distributions (KUDs)] and core activity areas were significantly larger for G. morhua (3·8 and 0·5 ha) than for G. ogac (2·7 and 0·3 ha). Home ranges were not related to total length (L_T) for G. morhua but showed a weak positive relationship for G. ogac. Gadus morhua occupied larger areas during the day while G. ogac occupied slightly larger areas at night. Mean rates of movement for G. ogac and G. morhua ranged from 0·83 to 1·24 and 0·76 to 1·76 L_T s^?1, respectively, and were highest during crepuscular periods. Overall, G. morhua were wider ranging, moved at faster rates and were active throughout the diel cycle compared to G. ogac of the same size. It is suggested that differential use of space and activity periods plays an important role in the successful coexistence of these two species.     

Interplay between ecological, behavioural and historical factors in shaping the genetic structure of sympatric walleye populations (Sander vitreus)

Disentangling ecological, behavioural and evolutionary factors responsible for the presence of stable population structure within wild populations has long been challenging to population geneticists. This study primarily aimed at decoding population structure of wild walleye (Sander vitreus) populations of Mistassini Lake (Québec, Canada) in order to define source populations to be used for the study of spatial partitioning using individual-based multilocus assignment methods, and decipher the dynamics of individual dispersal and resulting patterns of spatial resource partitioning and connectivity among populations. A second objective was to elucidate the relationships between biological characteristics (sex, size, age and population of origin) and an individual's probability to migrate and/or disperse. To do so, a total of 780 spawning individuals caught on five distinct spawning sites, and 1165 postspawning individuals, captured over two sampling seasons (2002-2003) were analysed by means of eight microsatellite loci. Four temporally stable walleye populations associated with distinct reproductive grounds were detected. These populations were differentially distributed among lake sectors during their feeding migration and their spatial distribution was stable over the two sampling seasons. Dispersing individuals were identified (n=61); these revealed asymmetrical patterns of dispersal between populations, which was also confirmed by divergent admixture proportions. Regression models underlined population of origin as the only factor explaining differential dispersal of individuals among populations. An analysis of covariance (ancova) indicated that larger individuals tended to migrate from their river of origin further away in the lake relative to smaller fish. In summary, this study underlined the relevance of using individual-based assignment methods for deciphering dynamics of connectivity among wild populations, especially regarding behavioural mechanisms such as differential spatial partitioning and dispersal responsible for the maintenance of genetic population structure.     

A review of the occurrence of inter‐colony segregation of seabird foraging areas and the implications for marine environmental impact assessment

Understanding the determinants of species’ distributions is a fundamental aim in ecology and a prerequisite for conservation but is particularly challenging in the marine environment. Advances in bio‐logging technology have resulted in a rapid increase in studies of seabird movement and distribution in recent years. Multi‐colony studies examining the effects of intra‐ and inter‐colony competition on distribution have found that several species exhibit inter‐colony segregation of foraging areas, rather than overlapping distributions. These findings are timely given the increasing rate of human exploitation of marine resources and the need to make robust assessments of likely impacts of proposed marine developments on biodiversity. Here we review the occurrence of foraging area segregation reported by published tracking studies in relation to the density‐dependent hinterland (DDH) model, which predicts that segregation occurs in response to inter‐colony competition, itself a function of colony size, distance from the colony and prey distribution. We found that inter‐colony foraging area segregation occurred in 79% of 39 studies. The frequency of occurrence was similar across the four seabird orders for which data were available, and included species with both smaller (10–100 km) and larger (100–1000 km) foraging ranges. Many predictions of the DDH model were confirmed, with examples of segregation in response to high levels of inter‐colony competition related to colony size and proximity, and enclosed landform restricting the extent of available habitat. Moreover, as predicted by the DDH model, inter‐colony overlap tended to occur where birds aggregated in highly productive areas, often remote from all colonies. The apparent prevalence of inter‐colony foraging segregation has important implications for assessment of impacts of marine development on protected seabird colonies. If a development area is accessible from multiple colonies, it may impact those colonies much more asymmetrically than previously supposed. Current impact assessment approaches that do not consider spatial inter‐colony segregation will therefore be subject to error. We recommend the collection of tracking data from multiple colonies and modelling of inter‐colony interactions to predict colony‐specific distributions.     

Inter‐individual variation in honey bee dance intensity correlates with expression of the foraging gene

Individual behavioural differences in responding to the same stimuli is an integral part of division of labour in eusocial insect colonies. Amongst honey bee nectar foragers, individuals strongly differ in their sucrose responsiveness, which correlates with strong differences in behavioural decisions. In this study, we explored whether the mechanisms underlying the regulation of foraging are linked to inter‐individual differences in the waggle dance activity of honey bee foragers. We first quantified the variation in dance activity amongst groups of foragers visiting an artificial feeder filled consecutively with different sucrose concentrations. We then determined, for these foragers, the sucrose responsiveness and the brain expression levels of three genes associated with food search and foraging; the foraging gene Amfor, octopamine receptor gene AmoctαR1 and insulin receptor AmInR‐2. As expected, foragers showed large inter‐individual differences in their dance activity, irrespective of the reward offered at the feeder. The sucrose responsiveness correlated positively with the intensity of the dance activity at the higher reward condition, with the more responsive foragers having a higher intensity of dancing. Out of the three genes tested, Amfor expression significantly correlated with dance activity, with more active dancers having lower expression levels. Our results show that dance and foraging behaviour in honey bees have similar mechanistic underpinnings and supports the hypothesis that the social communication behaviour of honey bees might have evolved by co‐opting behavioural modules involved in food search and foraging in solitary insects.     

Examining the link between dietary specialization and foraging modes of stream‐dwelling brown trout Salmo trutta

The aim of this study was to explore differences in dietary specialization across two foraging modes (benthic v. surface‐drift foraging) of stream‐dwelling brown trout Salmo trutta. The degree of inter‐individual niche variation within each foraging mode was high, but the dietary specialization was maintained between foraging modes. This study supports the view that if aquatic invertebrates are more abundant and accessible than surface prey, the individuals will not specialize on surface prey (surface‐drift foraging).     

Aphid colony turn‐over influences the spatial distribution of the grain aphid Sitobion avenae over the wheat growing season

1 Temporary habitats are characterized by the appearance and disappearance of patches in which resources are available for a limited period only. Organisms living in those environments usually exhibit adaptive traits, such as a high ability to find and exploit new patches. Among them are phytophagous insects, such as crop pests living in agroecosystems. Understanding how phytophagous insects invade a new patch is of great agricultural importance. 2 Here, we investigated how aphids colonize a wheat field by studying the spatial and temporal dynamics of their populations at large (field) and fine (group of host plants) scales. 3 The sampling design consisted of counting and locating aphid colonies within 30 0.25 m² squares randomly spaced in a 1.5‐ha winter wheat field over 2 months. All colonies were precisely located within the squares and their composition in terms of morphs was determined. 4 We show that: (i) immigration of winged aphids was a major factor driving the aphid population dynamics during a large part of the season and (ii) within the field, populations established late in the growing season. Aggregated, populations of aphids became progressively homogeneously distributed at the field scale. At the scale of a 0.25 m² square, infested plants were clustered in randomly distributed small patches, and aphid colonies experienced high extinction rates, suggesting failure in population establishment. 5 Because immigration may considerably influence both population dynamics and spatial distribution, our study suggests that future predictive models should give a greater weight to spring immigrants.     

Adjustment of pre‐moult foraging strategies in Macaroni Penguins Eudyptes chrysolophus according to locality,sex and breeding status

The annual moult creates the highest physiological stress during a penguin's breeding‐cycle and is preceded by a period of hyperphagia at sea. Although crucial to individual survival, foraging strategies before moult have been little investigated in keystone marine consumers in the Southern Ocean. The Macaroni Penguin Eudyptes chrysolophus demonstrates how individuals may adjust their foraging strategies during this period in line with constraints such as potential intraspecific competition between localities, foraging ability between dimorphic sexes and timing at sea between breeding and non‐breeding population components. We recorded pre‐moult behaviour at sea for 22 Macaroni Penguins from Crozet and Kerguelen Islands (southern Indian Ocean) during 2009 and 2011, using light‐based geolocation and stable isotope analysis. Penguins were distributed in population‐specific oceanic areas with similar surface temperatures (3.5 °C) south of the archipelagos, where they foraged at comparable trophic levels based on stable isotopes of their blood. Bayesian ‘broken stick’ modelling with concurrent analysis of seawater temperature records from the animal‐borne devices showed that within each population, females remained 6 days longer than males in the colder waters before heading back towards their colonies. Finally, 17 other non‐breeding individuals that moulted earlier had a higher mean blood δ¹⁵N value than did post‐breeding birds, meaning that early moulters probably fed more on fish than did late moulters. Our findings of such adjustments in foraging strategies developed across locality, sex and breeding status help understanding of the species' contrasted pre‐moult biology across its range and its ecology in the non‐breeding period.     

Space use by giant anteaters (Myrmecophaga tridactyla) in a protected area within human‐modified landscape

1. Spatial ecology data are essential for conservation purposes, especially when extinction risk is influenced by anthropogenic actions. Space use can reveal how individuals use the habitat, how they organize in space, and which components are key resources for the species.
2. We evaluated the space use and multiscale habitat selection of giant anteaters (Myrmecophaga tridactyla), a vulnerable Neotropical mammal, in a Cerrado site within a human‐modified landscape in southeastern Brazil.
3. We used GPS transmitters to track eight anteaters in the wild. With the resulting dataset, we estimated home range and core‐area sizes and then used two overlap indexes. We assessed habitat selection by compositional analysis and analyzed events of spatio‐temporal proximity.
4. The average Brownian bridge kernel estimate of home range size was 3.41 km² (0.92–7.9). Regarding home range establishment, five individuals showed resident behavior. Males (n = 4) had larger home ranges and were more active than females (n = 4). Despite the spatial overlap of home range (above 40% in four dyads), maximum temporal space sharing was 18%. Giant anteaters were found in proximity. Habitat selection favored savanna, and exotic timber plantation was always avoided. Roads and built‐up areas were selected secondarily at the landscape level.
5. The selection of anthropogenic sites denotes behavioral plasticity regarding modified habitats. However, the high selectivity for savanna, at all levels, demonstrates a high dependence on natural habitats, which provide the necessary resources for the species. The recurrent proximity of male–to‐female anteaters may indicate reproductive behavior, which is essential for maintaining this isolated population.

     

Inter‐Fullerene Electronic Coupling Controls the Efficiency of Photoinduced Charge Generation in Organic Bulk Heterojunctions

Photoinduced charge generation (PCG) dynamics are notoriously difficult to correlate with specific molecular properties in device relevant polymer:fullerene organic photovoltaic blend films due to the highly complex nature of the solid state blend morphology. Here, this study uses six judiciously selected trifluoromethylfullerenes blended with the prototypical polymer poly(3‐hexylthiophene) and measure the PCG dynamics in 50 fs–500 ns time scales with time‐resolved microwave conductivity and femtosecond transient absorption spectroscopy. The isomeric purity and thorough chemical characterization of the fullerenes used in this study allow for a detailed correlation between molecular properties, driving force, local intermolecular electronic coupling and, ultimately, the efficiency of PCG yield. The findings show that the molecular design of the fullerene not only determines inter‐fullerene electronic coupling, but also influences the decay dynamics of free holes in the donor phase even when the polymer microstructure remains unchanged.     

Diet of the Critically Endangered Brown Spider Monkey (Ateles hybridus) in an Inter‐Andean Lowland Rainforest in Colombia

Brown spider monkeys (Ateles hybridus) are one of the least known and more threatened primates in the Neotropics. Recognized as a species about a decade ago, field studies on these endangered primates have mainly focused on estimating local population densities. Since 2006, we habituated a group of wild brown spider monkeys at Serranía de Las Quinchas, Colombia, and studied their feeding ecology during 2.5 years using focal “subgroup” sampling, and conducted phenological surveys in order to estimate habitat‐wide fruit availability. Based on 847 hr of behavioral follows, brown spider monkeys spent approximately 25% of their time in feeding activities, and fed from fruits and leaves on at least 123 plant species. Ripe fruits were the most important item in the diet of A. hybridus at Las Quinchas comprising 92% of their feeding time. Probably due to the minor variation in the monthly proportion of fruits in brown spider monkey's diet throughout this study, there was no relation between habitat‐wide fruit availability and the proportion of fruit included in their monthly diet. The diet of brown spider monkeys at Las Quinchas is toward the high end of fruit intake, even within other wild spider monkeys’ populations, suggesting that these endangered primates might also be facing the challenges of being a large bodied fruit specialist under a regional scenario of habitat loss and fragmentation. Am. J. Primatol. 74:1097‐1105, 2012. © 2012 Wiley Periodicals, Inc.     

Sex‐related site fidelity of humpback whales (Megaptera novaeangliae) to the Fueguian Archipelago feeding area,Chile

We investigated sex‐related site fidelity by humpback whales to the Fueguian Archipelago, a new feeding area in the eastern South Pacific, by examining the resighting histories of 45 males and 39 females recorded from 2003 to 2012. Results indicated an overall annual return to the feeding area of 74.8%, and annual sex ratio is roughly equal in the population. The probability of an individual being resighted across years and in subsequent years was not significantly different for both males and females, however, the proportion of resighting within a year was significantly higher for individual males compared to females. Potential sources of sex‐related bias were analyzed, but none were found to be significant. Greater intraannual resighting frequency for males may reflect sex‐based differences in spatial occupation and short‐range movements due to potential differences in energy budgets.