Important Prey Items Research Articles

Diet of Nestling Spectacled Tyrants (Hymenops perspicillatus) in the Southeast Pampas Region, Argentina

We studied the diet of nestling Spectacled Tyrants (Hymenops perspicillatus) in the southeast Pampas region, Argentina. From November 2012 to January 2013, we used video footage to determine prey items that the parents fed to their chicks. We obtained 54 hrs of recording time to survey 18 nests. We identified a total of 125 prey items, representing 33 different taxa, grouped into four classes: Insecta, Arachnida, Chilopoda, and Amphibia. Insects accounted for 94% of total prey. The most frequent prey items were orthopterans (Caelifera), unidentified lepidopteran larvae, and odonats (Zygoptera). Lepidopterans were numerically the most important prey item in November, odonats in December, and orthopterans in January. Diet of the nestling birds was generalist in terms of the consumption of insects, and the changes in prey consumption during the course of the breeding season support an opportunistic feeding behavior by Spectacled Tyrants.

Associations of Bobolink Territory Size with Habitat Quality

Territory size generally varies with habitat quality, including vegetation structure, food abundance and available space. Bobolink (Dolichonyx oryzivorus), a semi-colonial species, is known to respond to these habitat quality factors individually, though no previous study has examined these factors simultaneously in relation to territory size. We examined the relationship between bobolink territory size and vegetation structure, prey abundance and patch size in hayfields of southern Ontario, Canada. All three factors were influential in explaining variation in territory size. Important prey items were more abundant in small territories. These small territories also had taller and denser vegetation, deeper litter, and less bare soil. Territory size was related to patch size, with smaller territories on smaller fields. We compared our results with other studies that have found links between territory size and individual variables, including factors not in our models.

Stomach content and stable isotope analysis of sailfish (Istiophorus platypterus) diet in eastern Taiwan waters

Stomach content analysis (SCA) and stable isotope analysis (SIA), coupled with isotopic-mixing model analysis, were used to estimate diet composition of sailfish Istiophorus platypterus in eastern Taiwan waters. SCA provided information on diet, but the high occurrence of empty stomachs (48.5%) limited this analysis. According to the index of relative importance (%IRI), the most important prey items were Priacanthus macracanthus (38.7%), followed by Auxis spp. (35.9%), and Trichiurus lepturus (8.5%). However, the most important prey groups for adult sailfish (>181cm, LJFL) as estimated by the stable isotope-mixing model were T. lepturus (32.6%), Katsuwonus pelamis (15.8%), and P. macracanthus (11.3%), and for maturing sailfish were K. pelamis (12.9%), P. macracanthus (10.4%), and T. lepturus (32.6%), respectively. Juvenile sailfish feed primarily on smaller prey items with lower δ15N values, while adult sailfish preferred larger prey items with higher δ15N values. Our findings suggested that an integrated SCA and SIA is considerably more powerful than using SCA alone in determining diet composition of sailfish over long time scales. In summary, a high diversity in the diet composition of sailfish was found and included an array of coastal, benthic, pelagic, and mesopelagic species. Sailfish are most likely opportunistic feeders consuming the most abundant prey items in eastern Taiwan waters.

Measurement of Diporeia respiration rate for Lake Superior

The freshwater amphipod Diporeia is a dominant macroinvertebrate species in Lake Superior’s benthic community and an important prey item for many fish. A capacity to predict growth and production rates of Diporeia using a bioenergetics model requires information on physiological processes of the species. The objective of this study is to quantify oxygen consumption of Lake Superior Diporeia and to determine if respiration rate changes with body length. Diporeia were collected from Lake Superior and kept over natural sediment maintained at 4°C. Dissolved oxygen levels for groups of immature (2mm), juvenile (4mm), and adult (6mm) Diporeia in 20ml microcosms were measured using a polarographic microelectrode. Mass-specific respiration rates for Lake Superior Diporeia ranged from 32.0 to 44.7 mg O2 g DW−1 day−1. A significant relationship between body length and mass-specific respiration rate (p>0.1) was not found. The estimate of Diporeia respiration presented here is significantly higher (p<0.05) than previous findings from populations in Lakes Michigan and Ontario. This study provides new data on respiration rates of Lake Superior Diporeia and compares findings to studies for other connecting Great Lakes.

Role of eutrophication in structuring planktonic communities in the presence of the ctenophore Mnemiopsis leidyi

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 510:151-165 (2014) - DOI: https://doi.org/10.3354/meps10900 Role of eutrophication in structuring planktonic communities in the presence of the ctenophore Mnemiopsis leidyi Marianne E. McNamara1,2,*, Darcy J. Lonsdale1, Robert M. Cerrato1 1School of Marine and Atmospheric Science, Stony Brook University, Stony Brook, NY 11794-5000, USA 2Biology Department, Suffolk County Community College, Selden, NY 11784, USA *Corresponding author: mcnamam@sunysuffolk.edu ABSTRACT: Increasing evidence implicates anthropogenic activities with recently documented shifts in the abundance and seasonal distribution of gelatinous zooplankton in coastal waters. The ctenophore Mnemiopsis leidyi occurs in mid-Atlantic estuaries in the USA where seasonal blooms occur earlier and in greater magnitude than those studied decades ago. Large densities of adult M. leidyi exert significant predation pressure on mesozooplankton, potentially influencing microplankton abundance and composition. Field-based mesocosm experiments were conducted to examine the individual and interactive roles of ctenophore predation and nutrient loading on the microplankton community using historic and recent abundances of M. leidyi in Great South Bay, New York, USA. High (recent) abundances of M. leidyi exposed to eutrophic conditions influenced plankton community structure in a way that was distinctly different from when the processes occurred separately or under low (historic) abundances. Microplanktonic ciliates exhibited an order of magnitude increase in tanks receiving either nutrient or ctenophore amendments, but increased by 2 orders of magnitude in treatments receiving both ctenophore and nutrient additions. Furthermore, ctenophores recovered from nutrient treatments produced nearly 3 times as many eggs than those reclaimed from ctenophore-only treatments, suggesting that nutrient enrichment enhances fecundity of M. leidyi. Since ciliates are an important prey item for developing M. leidyi, the combined bottom-up and top-down influences of eutrophication and ctenophore predation, respectively, on microplankton may help explain recently documented shifts in the population dynamics of M. leidyi in mid-Atlantic estuaries. KEY WORDS: Mesocosm · Ciliates · Trophic cascade · Mesozooplankton · Nutrient enrichment · Great South Bay Full text in pdf format PreviousNextCite this article as: McNamara ME, Lonsdale DJ, Cerrato RM (2014) Role of eutrophication in structuring planktonic communities in the presence of the ctenophore Mnemiopsis leidyi . Mar Ecol Prog Ser 510:151-165. https://doi.org/10.3354/meps10900 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 510. Online publication date: September 09, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

Prey Selection and Energy Values of Main Food Items of the Torrent Duck (Merganetta armata) in Northwestern Patagonia, Argentina

The Torrent Duck (Merganetta armata) is one of four species of waterfowl that live in fast flowing rivers. Torrent Ducks feed on benthic invertebrates in mountain rivers from Venezuela to Argentina. Prey selection by Torrent Ducks was investigated by comparing the proportion of prey taxa in their feces with the proportion available in river benthos. Feces and benthos were sampled during spring and autumn at sites with different precipitation levels in northwestern Argentine Patagonia. Energy values of the most important prey items were evaluated and the results adjusted for the amount of chitin body proportions. The average energy value of each individual prey item was 3.60 J in Gripopterygidae, 5.88 J in Simuliidae, 11.48 J in Atalophlebiinae and 12.25 J in Smicridea spp. These four invertebrate taxa represented approximately 80% of Torrent Duck diet. Prey availability and energy value alone could not explain the total Torrent Duck diet, and it was necessary to consider other factors such as aspects of prey natural history and their distribution in the benthos. Most consumed items were filter-feeding species (Simuliidae and Smicridea spp.) that inhabited rock surfaces that were more accessible to Torrent Ducks. Gripopterygidae and Atalophlebiinae were less accessible as they inhabit in the lower part of rocks. Diet information can be used to assess the availability of the most important prey items of Torrent Ducks in different rivers, and thus to estimate an important feature of habitat quality.

Impact on demersal fish of a large-scale and deep sand extraction site with ecosystem-based landscaped sandbars

For the seaward harbour extension of the Port of Rotterdam in the Netherlands, approximately 220 million m3 sand was extracted between 2009 and 2013. In order to decrease the surface area of direct impact, the authorities permitted deep sand extraction, down to 20 m below the seabed. Biological and physical impacts of large-scale and deep sand extraction are still being investigated and largely unknown. For this reason, we investigated the colonization of demersal fish in a deep sand extraction site. Two sandbars were artificially created by selective dredging, copying naturally occurring meso-scale bedforms to increase habitat heterogeneity and increasing post-dredging benthic and demersal fish species richness and biomass. Significant differences in demersal fish species assemblages in the sand extraction site were associated with variables such as water depth, median grain size, fraction of very fine sand, biomass of white furrow shell (Abra alba) and time after the cessation of sand extraction. Large quantities of undigested crushed white furrow shell fragments were found in all stomachs and intestines of plaice (Pleuronectes platessa), indicating that it is an important prey item. One and two years after cessation, a significant 20-fold increase in demersal fish biomass was observed in deep parts of the extraction site. In the troughs of a landscaped sandbar however, a significant drop in biomass down to reference levels and a significant change in species assemblage was observed two years after cessation. The fish assemblage at the crests of the sandbars differed significantly from the troughs with tub gurnard (Chelidonichthys lucerna) being a Dufrêne-Legendre indicator species of the crests. This is a first indication of the applicability of landscaping techniques to induce heterogeneity of the seabed although it remains difficult to draw a strong conclusion due the lack of replication in the experiment. A new ecological equilibrium is not reached after 2 years since biotic and abiotic variables are still adapting. To understand the final impact of deep and large-scale sand extraction on demersal fish, we recommend monitoring for a longer period, at least for a period of six years or even longer.

Diet of the South American sea lion Otaria flavescens during the summer season at Río Negro, Patagonia, Argentina

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 20:235-243 (2014) - DOI: https://doi.org/10.3354/ab00557 Diet of the South American sea lion Otaria flavescens during the summer season at Río Negro, Patagonia, Argentina Raimundo Lucas Bustos1,*, Gustavo Adolfo Daneri1, Alejandra Vanina Volpedo2, Ana Harrington1, Esperanza Amalia Varela1 1Museo Argentino de Ciencias Naturales ‘Bernardino Rivadavia’, Div. Mastozoología, Av. Angel Gallardo 470 (C1405DJR), Ciudad de Buenos Aires, Argentina 2Centro de estudios Transdisciplinarios del Agua-CONICET, Facultad de Ciencias Veterinarias, Universidad de Buenos Aires, Av. Chorroarín 280 (1428), Ciudad de Buenos Aires, Argentina *Corresponding author: lbustos@macn.gov.ar ABSTRACT: The South American sea lion Otaria flavescens population from northern Patagonia was under intensive commercial harvesting pressure between 1930 and 1950 and is currently increasing at a rate of nearly 6% yr-1. Food availability in the oceans is one of the most important factors influencing the survival and dynamics of marine mammal populations. The objective of the present study was to determine the summer diet of O. flavescens by faecal analysis, in order to assess its trophic behavior, determine whether there are interannual differences in diet composition, and evaluate the potential interaction between fisheries operating in the study area and the species. Present results show that O. flavescens preys mainly on fish species, with Raneya brasiliensis being the most frequent (frequency of occurrence, %FO = 65.7) and abundant (%N = 47.9) fish prey. Cephalopods were the second most important prey item in terms of %FO (42.6%), with the highest index of relative importance corresponding to the octopod Octopus tehuelches. Since these prey taxa are not targeted by the commercial fishing fleet that operates in the study area, the overlap in the use of resources by O. flavescens and fisheries may not be substantial. Given that the biomass of the prey species mentioned above is not directly affected by fishery activities during summer, a greater amount of food may be available for sea lions, with this factor possibly contributing to the population recovery in the area. KEY WORDS: Otaria flavescens · Summer diet · Scats · Patagonia · Argentina Full text in pdf format PreviousNextCite this article as: Bustos RL, Daneri GA, Volpedo AV, Harrington A, Varela EA (2014) Diet of the South American sea lion Otaria flavescens during the summer season at Río Negro, Patagonia, Argentina. Aquat Biol 20:235-243. https://doi.org/10.3354/ab00557 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 20, No. 3. Online publication date: May 07, 2014 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2014 Inter-Research.

The Early Marine Biology of the Hatchery/Wild Juvenile Salmonid (Oncorhynchus sp.) Community in Barkley Sound, Canada

We conducted 11 purse seine/beachseine surveys over the summers of 2000 and 2001 to learn about the migration timing, distribution, and diet of hatchery chinook (Oncorhynchus tshawytscha) and coho (O. kisutch), and wild chinook, coho, sockeye (O. nerka) and chum (O. keta) juvenile salmon, in Barkley Sound, West Coast Vancouver Island. Juvenile salmon partitioned Barkley Sound by time and space, and by diet except for hatchery and wild coho. The analysis of migration timing included historic data for 1987-89, and results showed that timing differed between species and was consistent over years. Sockeye and chum dominated the juvenile salmon community until mid-June and hatchery and wild chinook dominated subsequently. Fish tended to be dispersed contagiously. Results of correlation analyses of catch suggested that fish of different origins and species did not co-occur. The euphausiid Thysanoessa spinifera was an important prey item but different fish species selected different sizes of T. spinifera at different times. The diet overlap between hatchery and wild coho did not affect return. Migration timing for sockeye and wild coho seems to reflect a strategy to enter the ocean when the biomass of the size fraction of T. spinifera that each species selects is likely to be maximal. Descriptions of migration timing, fish interactions, and diet provide information which appears to be useful for learning about the biological basis of salmon return variability.

Feeding habits of the king soldier bream, Argyrops spinifer (Forsskål, 1775) (Perciformes: Sparidae), in the northern Persian Gulf

Summary The feeding habits of the king soldier bream Argyrops spinifer (Forssk al, 1775), were examined in the northern part of the Persian Gulf (coastal waters of Bushehr, Iran). The stomach contents of 622 specimens, 13.5–64.2 cm in total length, collected by a trawl boat from June 2010 to May 2011, were analysed to assess the influence of size, season and sex on their diet composition. Amongst the examined stomachs, 57 were empty (vacuity index = 9.2%), which varied significantly (P < 0.05) throughout the year. According to the results, this species is a generalist carnivorous feeder with a diet consisting of 52 different prey items belonging to nine main categories. Bivalvia, Gastropoda, Malacostraca, Crustacea and Teleostei were the most important prey items. Fish size and gender showed no significant effects on diet composition. Moreover, in the main food catagories no seasonal variations were detected.

Cover type, environmental characteristics, and conservation of terrestrial gastropod diversity in boreal mixedwood forests

Terrestrial gastropods are important decomposers, herbivores, and prey items in forest systems and constitute a poorly understood element of forest biodiversity in Canada. We sampled terrestrial gastropod assemblages in northwestern Alberta, Canada, using board traps and forest floor sampling to examine their association with forest composition, structure, and environment (forest floor depth and moisture, coarse woody debris, understory vegetation cover) in four boreal mixedwood cover types: broadleaf (deciduous) dominated (DDOM), broadleaf (deciduous) dominated with coniferous understory (DDOMU), mixed conifer and broadleaf (MX), and conifer dominated (CDOM). The highest total gastropod abundance and richness occurred in the DDOM cover type. Furthermore, DDOM assemblages accumulated species more quickly (with sampling effort) and supported more gastropod species at higher levels of dominance than found in other cover types. The mix of coniferous and broadleaved trees influenced gastropod distributions within stands; however, associations observed between gastropod species and tree species differed among cover types, suggesting complex ecological contingency. For example, conifer basal area was an important driver of gastropod assemblage in DDOM and DDOMU forests, whereas broadleaf basal area was the most important driver in the CDOM forest type. We conclude that tree species mixture at a variety of scales sustains diversity of gastropod assemblages and that this understanding is significant for conservation of this taxon on mixedwood boreal forest landscapes.

Difference in Black-tailed Gull (Larus crassirostris) diet during the breeding season for the last 10 years in the South Sea of Korea

Sea temperature in the South Sea of Korea has been increased over the last decades. Seabirds are sensitive to changes in food availability in marine environment. In this study, we investigate the diet of Black-tailed gulls (Larus crassirostris) during the breeding season to identify changes of marine environment and biological response such as breeding performance in the South Sea of Korea. A total of 22 fish species or family (n = 128) from regurgitates by chicks were collected on Hongdo Island in 2002 and 2012. The most important prey item was Japanese anchovies (Engraulis japonicas). Proportion of Anchovy in diet increased in 2012 (70.5%) compared to 10 years ago (27.5%). Some species were newly found in 2012: Spotted chub mackerel (Scomber australasicus), Pacific sand lace (Ammodytes personatus), White ventral goby (Acanthogobius lactipes), Silver-strip round herring, Multicolorfin rainbowfish (Halichoeres poecilopterus), Silverside (Hypoatherina tsurugae), Surfperch (Neoditrema ransonneti) and Spotnape ponyfish (Leiognathus muchalis), but not in 2002. Especially, sub-tropic fish such as Kammal thryssa (Thryssa kammalensis), and Rosefish (Helicolenus hilgendorfi) were frequently observed in the diet of 2012. These results might reflect the increase of sea temperature in the South Sea of Korea.

The diet of the black widow spider Latrodectus mirabilis (Theridiidae) in two cereal crops of central Argentina

The spider Latrodectus mirabilis (Holmberg, 1876) is commonly found in cereals crops of central Argentina. We studied its diet composition at the field and capture rate on leaf-cutting ants based on laboratory experiments. This study comprises the first approach that documents the diet of L. mirabilis in wheat and oat fields of central Argentina. We identified 1,004 prey items collected from its webs during the last phenological stages of both cereal crops. The prey composition was variable but the spiders prey mainly on ants (Formicidae, Hymenoptera), who represented more than 86% of the total. Meanwhile, in the capture rate experiences we registered a high proportion of ants captured by spiders at the beginning of experiences, capturing the half of the ants from total in the first four hours. Summarizing, we reported a polyphagous diet of this spider species in wheat and oat fields. Ants were the most important prey item of this spider, as found in other Latrodectus spiders around the world.

Distribution and feeding ecology of the Greenland shark (Somniosus microcephalus) in Greenland waters

Greenland sharks are widely distributed and most likely a highly abundant predator in arctic waters. Greenland sharks have previously been considered scavengers, but recent studies suggest that Greenland sharks also predate on live prey. In this study, distribution and feeding ecology in Greenland waters were investigated. Based on data from 25 years of surveys, Greenland sharks were usually caught at 400–700 m but were found at all depths between 100 and 1,200 m. Based on examination of stomachs from 30 Greenland sharks (total length of 258–460 cm), the most important prey items were Atlantic cod (65.6 % IRI), harp seal (9.9 % IRI), skates (5.2 % IRI) and wolffish (4.4 % IRI), but large geographical variations were observed. Prey composition and qualitative observations support the hypothesis of active predation. Consistent with other studies, the results of this work support the notion that the Greenland shark is an apex predator with the potential to influence trophic dynamics in the Arctic.

Feeding habits of juvenile Japanese common squid Todarodes pacificus: Relationship between dietary shift and allometric growth

In this study, ontogenetic dietary shifts in relation to morphological changes were examined in juvenile Japanese common squid Todarodes pacificus (<160mm mantle length; ML) collected in the Sea of Japan. Ten morphometric characters were measured for 147 specimens of Japanese common squid. The allometric growth pattern of each character in relation to ML was studied by using the logarithmic form of the allometric growth model with piecewise regression analysis. The allometric growth pattern indicated that the body shape of T. pacificus changed from a rounded to a more streamlined shape, and only growth of the fin base length and fin width were positively allometric. Three morphological characters had an inflection point at 53–72mm ML, indicating the transformation to an adult morphology. The digestive tract contents of 135 squids were examined for dietary shifts. T. pacificus smaller than 50mm ML fed exclusively on crustaceans such as copepods, amphipods and euphausiids, and then shifted to a mixed diet of crustaceans and fish at 50–99mm ML; after reaching 100mm ML, fish were the most important prey items and crustaceans became less important. These suggest that the swimming performance of T. pacificus changes markedly at around inflection points, the size at which T. pacificus starts to feed on fish. Therefore, the dietary shift is suggested to be closely related to the ontogenetic change in swimming performance.

Prey preferences of sympatric fin (Balaenoptera physalus) and humpback (Megaptera novaeangliae) whales revealed by stable isotope mixing models

AbstractOver‐exploitation of top predators and fish stocks has altered ecosystems towards less productive systems with fewer trophic levels. In the Celtic Sea (CS), discards and bycatch levels have prompted concern about some fisheries, while fin and humpback whales are recovering from centuries of over‐exploitation. A lack of empirical evidence on the preferred diet of some predators such as whales in the CS has hindered the implementation of effective conservation measures using an ecosystem‐based approach to fisheries management. Using a Bayesian framework (SIAR), stable carbon (δ13C) and nitrogen (δ15N) isotope mixing models were used to assign proportionate diet solutions to fin and humpback whales (skin biopsies) and putative prey items: herring (Clupea harengus), sprat (Sprattus sprattus), and krill (Meganyctiphanes norvegica and Nyctiphanes couchii) in the CS. Krill was the single most important prey item in the diet of fin whales, but one of the least important for humpback whales (albeit based on a small sample of humpback whale samples). Age 0 sprat and herring comprised a large proportion of the diet of both species, followed by older sprat (age 1–2) and older herring (age 2–4). An ecosystem based approach to fisheries management will be required in the CS if we seek effective conservation of both fin and humpback whales, and sustainable fisheries.

Pelagic decapods in the northern Benguela upwelling system: Distribution, ecophysiology and contribution to active carbon flux

Decapods were sampled with a 1m2 MOCNESS (mainly upper 1000m) in the northern Benguela Current during three cruises in December 2009, September/October 2010 and February 2011. Although pelagic decapods are abundant members of the micronekton community, information about their ecophysiology is very limited. Species-specific regional distribution limits were detected for various decapod species (e.g. Plesionika carinata, Sergestes arcticus, Pasiphaea semispinosa). Significant diel vertical migration patterns were determined for three caridean and three penaeiodean species. Biomass was variable and ranged from 23 to 2770mg dry mass m−2 with highest values for P. semispinosa. Fatty acid and stable isotope analyses revealed that the examined decapod species are omnivorous to carnivorous except for the herbivorous to omnivorous species P. carinata. Calanid copepods such as Calanoides carinatus were identified as an important prey item especially for caridean species. Community consumption rates of pelagic decapods derived from respiration rates ranged from 7mgCm−2d−1 (23°S) to >20mgCm−2d−1 (19°S, 17°S). A potential active respiratory carbon flux was calculated for migrating pelagic decapods with 4.4mgCm−2d−1 for the upper 200m and with 2.6mgCm−2d−1 from the base of the euphotic zone to a depth of 600m. Overall, pelagic decapods apparently play a more prominent role in the northern Benguela Current ecosystem than previously assumed and may exert a substantial predation impact on calanid copepods (up to 13%d−1 of standing stock).

Lesser black-backed gulls (Larus fuscus) consuming swimming crabs: An important link in the food web of the southern North Sea

Swimming crabs (Liocarcinus spp.) are one of the most common brachyuran species in the North Sea, and their abundance has substantially increased over the last century. Seabirds such as lesser black-backed gulls (LBBG) commonly feed mainly on higher-trophic-level organisms such as fish. However, intensive use of swimming crabs by LBBGs in the eastern North Sea has been noted over several years. Our investigation of this aspect of the food web by examining food remains from breeding LBBGs showed that swimming crabs accounted for more than half of the nutrition of LBBGs. Gulls selected larger individuals than expected, based on sizes of free-living swimming crabs. A long-term data set (2002–2006) shows that gulls took swimming crabs mainly in the early morning and late evening, suggesting that they might migrate vertically in the water column. Moreover, it shows that although swimming crabs occurred at considerable distances from the shore, LBBGs took this prey item exclusively from near the shore where it was most abundant. This suggests the existence of a possible energy threshold above which gulls experience a net energy loss, if they have to travel too far from their colony, where the abundance of swimming crabs is lower and the energy intake might thus not compensate for the long-distance flights. Swimming-crab abundance did not appear to be the primary factor influencing overall gull distribution. A simple bioenergetic model showed that the 22,000 individual LBBGs in the most important breeding colony in the south-eastern North Sea consumed approximately 35 million swimming crabs annually (i.e. 1590 swimming crabs per individual gull) during the breeding period. However, considering the high numbers of swimming crabs in the south-eastern North Sea (demonstrated by bottom-trawl surveys in 2005 and 2007) LBBGs are unlikely to exert top-down control on this prey. Conversely, a bottom-up effect is more likely, potentially enabling further increases in LBBG populations through increases in their most important prey item in the south-eastern North Sea.

Diet and trophic niche of Antarctic silverfish Pleuragramma antarcticum in the Ross Sea, Antarctica

The diet of Antarctic silverfish Pleuragramma antarcticum was evaluated by examining stomach contents of specimens collected in the Ross Sea (71°-77° S; 165°-180° E) in January to March 2008. Pleuragramma antarcticum (50-236 mm standard length, L(S)) and prey items were analysed for stable-isotopic composition of carbon and nitrogen. According to index of relative importance (I(RI) ), which incorporates frequency of occurrence, mass and number of prey items, the most important prey items were copepods (81%I(RI) over all specimens), predominantly Metridia gerlachei and Paraeuchaeta sp., with krill and fishes having low I(RI) (2·2 and 5·6%I(RI) overall). According to mass of prey (M) in stomachs, however, fishes (P. antarcticum and myctophids) and krill dominated overall diet (48 and 22%M, respectively), with copepods being a relatively minor constituent of overall diet by mass (9·9%M). Piscivory by P. antarcticum occurred mainly in the extreme south-west of the region and near the continental slope. Krill identified to species level in P. antarcticum stomachs were predominantly Euphausia superba (14·1%M) with some Euphausia crystallophorias (4·8%M). Both DistLM modelling (PRIMER-permanova+) on stomach contents (by I(RI)) and stepwise generalized linear modelling on stable isotopes showed that L(S) and location were significant predictors of P. antarcticum diet. Postlarval P. antarcticum (50-89 mm L(S)) consumed exclusively copepods. Juvenile P. antarcticum (90-151 mm L(S)) consumed predominantly krill and copepods by mass (46 and 30%M, respectively). Small adult P. antarcticum (152-178 mm L(S)) consumed krill, fishes and copepods (37, 36 and 15%M, respectively). Large adult P. antarcticum (179-236 mm L(S)) consumed predominantly fishes and krill (55 and 17%M, respectively), especially in the north (near the Ross Sea slope) and in the SW Ross Sea. Amphipods were occasionally important prey items for P. antarcticum (western Ross Sea, 39%M). General concordance between stomach contents and trophic level of P. antarcticum and prey based on δ(15) N was demonstrated. Pleuragramma antarcticum trophic level was estimated as 3·7 (postlarval fish) and 4·1 (fish aged 3+ years).

The invertebrate diet of northern bobwhite chicks in Georgia, United States

The establishment of brood–rearing habitats along field margins has become a popular agri–environmental prescription to help reverse population declines of northern bobwhite (Colinus virginianus) in Georgia, United States. Here, the invertebrate–diet of chicks foraging on farmland with established brood–rearing habitats is examined and compared to those of chicks on an intensively managed wild bobwhite shooting estate. In 2001 and 2002, faecal samples were collected and analysed from nocturnal roost sites of bobwhite broods. Differences in invertebrate composition between the study sites were investigated using compositional analysis. While the diet of chicks on both sites contained similar invertebrate groups, the composition of the diets varied significantly. Although chicks on farmland had eaten 1.7 times fewer Coleoptera, they had 1.7 times more Hemiptera in their diet. These data suggest that although the invertebrate composition in the diet of chicks differed between the two landscapes, both contained high proportions of important prey items.