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Hawksbill sea turtles are the most tropical sea turtle species with one of the last remaining aggregations in West Africa found on Príncipe Island (1° 37′ N; 7° 23′ E). Here we present for the first time, data on the trophic and foraging ecology of both juvenile and adult hawksbill turtles found in the shallow waters of Príncipe, using stable isotope analyses of carbon (δ 13 C) and nitrogen (δ 15 N), and assess any isotopic niche segregation between these two life-stages. Hawksbill turtles were sampled from December 2012 to June 2014, complementary to a snorkeling survey conducted around the entire coastline ( ca . 100 km). δ 13 C and δ 15 N values were measured in epidermal samples of 40 individuals and analyzed in the context of isotopic niche width and overlap (i.e. trophic and foraging niches). Juveniles hawksbills (n = 29; < 60 cm curved carapace length (CCL)) occupy a significant smaller isotopic niche than adults (n = 11; > 75 cm), especially in relation to δ 13 C values (i.e. habitat use) but also in δ 15 N values (i.e. trophic level). Variances between adults and juveniles were not homogenous for both isotopes and larger for adults, particularly for δ 13 C values. We found significant differences in δ 13 C values between the two groups, but not for δ 15 N, and a significant correlation between δ 13 C values and CCL for the pooled data. SIBER (stable isotopes Bayesian ellipses in R) outcomes support these results and, although niches are not completely segregated, it indicates spatial foraging segregation between juveniles and adults. The fact that Príncipe Island's shallow waters are constantly being patrolled by spearfishermen, together with the existence of a large insular platform and a superior dive capacity in larger hawksbills, might influence this segregation. Our results suggest that part of the adults may be originating from isotopically distinct areas. To have a better understanding on the distribution and abundance of the sea turtle populations in Príncipe, including their connectivity with other foraging and breeding areas, future in-water studies focused mainly on the entire insular platform of Príncipe, but also on the adjacent probable foraging areas of the Gulf of Guinea, are required. [ABSTRACT FROM AUTHOR]

Knowledge about sexual segregation and gender-specific, or indeed individual specialization, in marine organisms has improved considerably in the past decade. In this context, we tested the “Intersexual Competition Hypothesis” for penguins by investigating the feeding ecology of Gentoo penguins during their austral winter non-breeding season. We considered this during unusual environmental conditions (i.e. the year 2009 had observations of high sea surface and air temperatures) in comparison with the long term average at Bird Island, South Georgia. Through conventional (i.e. stomach contents) and stable isotopic values from red blood cells, plasma and feathers of both male and female Gentoo penguins, we showed that there were significant differences between sexes, with males feeding mainly on fish (54% by mass) followed by crustaceans (38%) whereas females fed mainly on crustaceans (89% by mass) followed by fish (4%). Themisto gaudichaudii was the most important crustacean prey for males (64% by mass; 82% by number; 53% by frequency of occurrence) and females (63% by mass; 77% by number; 89% by frequency of occurrence), contrasting with all previous studies that found Antarctic krill Euphausia superba were generally the main prey. Stable isotopic data showed that, in terms of habitat use (based on δ 13C), there were significant differences in short-term carbon signatures between males and females (based on plasma and red blood cells), suggesting that both sexes explored different habitats, with females exploring more offshore pelagic waters and males feeding more in coastal benthic waters. Based on δ 15N, males fed on significantly higher trophic level than females (based on plasma and red blood cells), in agreement with our diet results., Thus, Gentoo penguins behave in a similar manner to other non-breeding penguins species (e.g. king, macaroni and rockhopper penguins), albeit at a smaller spatial scale (as they do not disperse as these other penguins do), in that they have a wider habitat and trophic niche during the Antarctic Winter (in comparison to Summer). We also detected individual specialization in feeding/trophic levels for each gender, with certain males feeding mainly on fish and certain females mainly on crustaceans, which may be driven the prevailing environmental conditions that lead individuals to search for alternative prey, and cause sexual diet segregation. Our results provide further information to help improve understanding about sexual segregation and individual specialization of marine organisms, while contributing valuable information on the winter diet for Antarctic monitoring programs and for modelling Antarctic marine food webs. [ABSTRACT FROM AUTHOR]

Rationale The main limitation of isotopic tracking for inferring distribution is the lack of detailed reference maps of the isotopic landscape (i.e. isoscapes) in the marine environment. Here, we attempt to map the marine δ13C isoscape for the southwestern sector of the Atlantic Ocean, and assess any temporal variation using the wandering albatross as a model species. Methods Tracking data and blood and diet samples were collected monthly from wandering albatrosses rearing chicks at Bird Island, South Georgia, during the austral winter between May and October 2009. The δ13C and δ15N values were measured by mass spectrometry in plasma and blood cells, and related to highly accurate data on individual movements and feeding activity obtained using three types of device: GPS, activity (immersion) loggers and stomach temperature probes. Results The tracked birds foraged in waters to the north or northwest of South Georgia, including the Patagonian shelf-break, as far as 2000 km from the colony. The foraging region encompassed the two main fronts in the Southern Ocean (Polar and Subantarctic fronts). The δ13C values varied by only 2.1 ‰ in plasma and 2.5 ‰ in blood cells, and no relationships were found between the δ13C values in plasma and the mean latitude or longitude of landings or feeding events of each individual. Conclusions The failure to distinguish a major biogeographic gradient in δ13C values suggest that these values in the south Atlantic Ocean are fairly homogeneous. There was no substantial variation among months in either the δ13C or the δ15N values of plasma or blood cells of tracked birds. As birds did not show a significant change in diet composition or foraging areas during the study period, these results provide no evidence for major temporal variation in stable isotope ratios in consumer tissues, or in the regional marine isoscape in the austral winter of 2009. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Trophic relationships are a central theme in ecology and play a crucial role in the survival of organisms, because the availability of food resources varies over time and space. Until recently, most ecological studies treated conspecific individuals as ecologically equivalent, but intra-specific variation in individual foraging and feeding strategies can be large. Studies documenting the occurrence of individual specialization in seabirds ( n = 94) increased substantially since the year 2000, and rapid and significant advances are being made since then. This review summarizes existing knowledge within this subject, examines the relative incidence of individual specialization and investigates the possible ecological implications of individual specialization in seabirds. Our results show that, to date, the incidence of individual specialization is documented in around 12 % of the total extant seabird species although some studies ( n = 12) did not find evidences of individual specialization in the foraging and feeding strategies of some seabird populations. Most studies were conducted at higher latitudes, leading to a lack of knowledge on the incidence of this trait in tropical seabird populations. Results suggest that the incidence of individual specialization may be potentially widespread within seabirds, but may fluctuate spatio-temporally among/within species and populations due to the frequency of specialists, predictability of resources or environmental conditions. This study supports the hypothesis that individual specialization may have important ecological consequences at both individual and population levels, such as implications in breeding performance or in intra-specific competition and, consequently, a high impact on ecological processes and foraging dynamics. Further investigation is required to identify the mechanisms that generate individual specialization and its ecological implications at both population and individual levels. [ABSTRACT FROM AUTHOR]

Breeding seabirds are central-place foragers and therefore exploit food resources most intensively nearer their colonies. When nesting aggregations are close to one another density-dependent competition is likely to be high, potentially promoting foraging segregation (i.e. neighbouring colonies may segregate to search for food in different areas). However, little is known about spatial segregation in foraging behaviour between closely adjacent colonies, particularly in species that are wide-ranging foragers. Here, we tested for foraging segregation between two sub-colonies of a wide-ranging seabird, Cory's shearwater Calonectris borealis, separated by only 2 km, on a small Island in the North Atlantic. During the 2010 chick-rearing period, 43 breeding adults of both sexes were simultaneously sampled at both sub-colonies. A GPS logger was deployed on each individual and removed after several foraging trips at sea. Blood samples (plasma and red blood cells) were collected from each tracked individual for stable isotope analysis. Results indicated partial spatial segregation between the two sub-colonies during local foraging trips (i.e. those of ≤1 day duration and 216 km from the colony) accounting for 84.2 % of all trips recorded. The location of the breeding sub-colony influenced the direction of travel of birds during local trips resulting in sub-colony-specific foraging areas. Although the oceanographic conditions associated with the foraging range of the two sub-colonies differed, no differences were found in the habitat exploited and in their estimated diets. This suggests that birds concentrated their feeding activity in patches of similar habitat and prey during the chick-rearing period. [ABSTRACT FROM AUTHOR]

This study tested for fluctuations on short-term consistency (within about 1 month) in the isotopic niche of a pelagic seabird species. Short-term consistency in the isotopic niche was assessed using a wide-ranging apex predator, the Cory's shearwaters Calonectris diomedea, along a 3-year study (2010-2012), during both the pre-laying and chick-rearing periods, with markedly inter- and intra-annual differences in the foraging spatial distribution at sea and isotopic niche width. We used individual movement data and stable isotope data, analysed using recent metrics based in a Bayesian framework, of 69 adults breeding on a small neritic island in the North Atlantic (39°24′N, 009°30′W). As expected, our results confirm that isotopic niche expansion could arise via increased variation in spatial distribution at sea among individuals. Results suggest fluctuations on short-term consistency in the isotopic niche of Cory's shearwaters related to their different foraging patterns among periods and, ultimately, to presumably temporal changes in the availability and predictability of food resources. Short-term consistency in the isotopic niche was higher and persistent during periods when the population showed an intermediate isotopic niche width and absent when isotopic niche was either smaller or larger during the study period. These results suggest that consistency in the isotopic niche is an important characteristic of this population during the breeding period that may fluctuate depending on resources availability and should be important to understand the dynamics of foraging ecology of pelagic seabirds in general. [ABSTRACT FROM AUTHOR]

The wandering albatross ( Diomedea exulans) is regarded as a generalist predator, but can it be consistent in its foraging niche at an individual level? This study tested short- and long-term consistency in the foraging niche in terms of habitat use, trophic level and, by inference, prey selection. Fieldwork was carried out at Bird Island, South Georgia, in May-October 2009, during the chick-rearing period. Blood (plasma and cells) and feathers for stable isotope analyses (δC and δN) were sampled from 35 adults on their return from a foraging trip during which they carried stomach temperature, activity and global positioning system loggers. Results suggest short-term consistency in foraging niche in relation to both oceanic water mass and trophic level, and long-term consistency in use of habitat. Consistent differences between individuals partly reflected sex-specific habitat preferences. The proportion of consistent individuals (i.e., with a narrow foraging niche) was estimated at c. 40 % for short-term habitat and trophic level (prey) preferences and 29 % for longer-term habitat preference, suggesting this is an important characteristic of this population and potentially of pelagic seabirds in general. Foraging consistency was not related to body condition or level of breeding experience; instead, it may reduce intraspecific competition. [ABSTRACT FROM AUTHOR]