Movements of wintering surf scoters: predator responses to different prey landscapes

The distribution of predators is widely recognized to be intimately linked to the distribution of their prey. Foraging theory suggests that predators will modify their behaviors, including movements, to optimize net energy intake when faced with variation in prey attributes or abundance. While many studies have documented changes in movement patterns of animals in response to temporal changes in food, very few have contrasted movements of a single predator species naturally occurring in dramatically different prey landscapes. We documented variation in the winter movements, foraging range size, site fidelity, and distribution patterns of a molluscivorous sea duck, the surf scoter (Melanitta perspicillata), in two areas of coastal British Columbia with very different shellfish prey features. Baynes Sound has extensive tidal flats with abundant clams, which are high-quality and temporally stable prey for scoters. Malaspina Inlet is a rocky fjord-like inlet where scoters consume mussels that are superabundant and easily accessible in some patches but are heavily depleted over the course of winter. We used radio telemetry to track surf scoter movements in both areas and found that in the clam habitats of Baynes Sound, surf scoters exhibited limited movement, small winter ranges, strong foraging site fidelity, and very consistent distribution patterns. By contrast, in mussel habitats in the Malaspina Inlet, surf scoters displayed more movement, larger ranges, little fidelity to specific foraging sites, and more variable distribution patterns. We conclude that features associated with the different prey types, particularly the higher depletion rates of mussels, strongly influenced seasonal space use patterns. These findings are consistent with foraging theory and confirm that predator behavior, specifically movements, is environmentally mediated.     

Modeling spring migration patterns of scoters and loons in the Bay of Fundy

Populations of scoter and loon species that winter in the Atlantic are understudied in North America, but coastal observatories may provide the data required to fill some of the knowledge gaps. The migration of scoters and loons has been monitored at the Point Lepreau Bird Observatory (PLBO) in the Bay of Fundy every spring since 1996, but little peer-reviewed research based on the resultant database has been published. Using data collected over 18 years at the Bay of Fundy (2000–2017), our objectives were to (1) determine the most accurate method of modeling hourly migration rates for Surf (Melanitta perspicillata), White-winged (M. deglandi), and Black (M. americana) scoters, and Red-throated (Gavia stellata) and Common (G. immer) loons, and (2) assess trends in hourly migration rates for our five focal species to determine if the numbers of migrants passing PLBO have changed over time. We calculated hourly migration rates for each of our five focal species and evaluated drivers (i.e., timing and environmental conditions) of migration and annual trends using zero-inflated generalized linear mixed models (GLMMs). We found that drivers of migration differed among species. Specifically, hourly migration rates decreased with increasing tide height for all species except Red-throated Loons. In addition, hourly migration rates increased with increasing wind vector (i.e., a tailwind) for the three scoter species, but decreased with increasing wind vector for the two loon species. Scoter migration rates peaked daily between 11:00 and 13:00 UTC, but we found no daily peak for either loon species. Peak hourly migration rates of Black and Surf scoters occurred from 12 to 26 April, but migration rates of White-winged Scoters and both loon species continued to increase throughout our migration-monitoring window. Finally, we found no changes in hourly migration rates over time for any of our focal species, suggesting no changes in abundance over the 18 years of data collection. Our study reveals the importance and utility of long-term, coastal observation stations, and we recommend their continued funding and use as valuable sources of monitoring data.     

Coast to coast: High genomic connectivity in North American scoters

Dispersal shapes demographic processes and therefore is fundamental to understanding biological, ecological, and evolutionary processes acting within populations. However, assessing population connectivity in scoters (Melanitta sp.) is challenging as these species have large spatial distributions that span remote landscapes, have varying nesting distributions (disjunct vs. continuous), exhibit unknown levels of dispersal, and vary in the timing of the formation of pair bonds (winter vs. fall/spring migration) that may influence the distribution of genetic diversity. Here, we used double‐digest restriction‐associated DNA sequence (ddRAD) and microsatellite genotype data to assess population structure within the three North American species of scoter (black scoter, M. americana; white‐winged scoter, M. deglandi; surf scoter, M. perspicillata), and between their European congeners (common scoter, M. nigra; velvet scoter, M. fusca). We uncovered no or weak genomic structure (ddRAD Φ_ST < 0.019; microsatellite F_ST < 0.004) within North America but high levels of structure among European congeners (ddRAD Φ_ST > 0.155, microsatellite F_ST > 0.086). The pattern of limited genomic structure within North America is shared with other sea duck species and is often attributed to male‐biased dispersal. Further, migratory tendencies (east vs. west) of female surf and white‐winged scoters in central Canada are known to vary across years, providing additional opportunities for intracontinental dispersal and a mechanism for the maintenance of genomic connectivity across North America. In contrast, the black scoter had relatively elevated levels of divergence between Alaska and Atlantic sites and a second genetic cluster found in Alaska at ddRAD loci was concordant with its disjunct breeding distribution suggestive of a dispersal barrier (behavioral or physical). Although scoter populations appear to be connected through a dispersal network, a small percentage (<4%) of ddRAD loci had elevated divergence which may be useful in linking areas (nesting, molting, staging, and wintering) throughout the annual cycle.     

Annual-Cycle Movements and Phenology of Black Scoters in Eastern North America

Sea ducks exhibit complex movement patterns throughout their annual cycle; most species use distinct molting and staging sites during migration and disjunct breeding and wintering sites. Although research on black scoters (Melanitta americana) has investigated movements and habitat selection during winter, little is known about their annual-cycle movements. We used satellite telemetry to identify individual variation in migratory routes and breeding areas for black scoters wintering along the Atlantic Coast, to assess migratory connectivity among wintering, staging, breeding, and molt sites, and to examine effects of breeding site attendance on movement patterns and phenology. Black scoters occupied wintering areas from Canadian Maritime provinces to the southeastern United States. Males used an average of 2.5 distinct winter areas compared to 1.1 areas for females, and within-winter movements averaged 1,256 km/individual. Individuals used an average of 2.1 staging sites during the 45-day pre-breeding migration period, and almost all were detected in the Gulf of St. Lawrence. Males spent less time at breeding sites and departed them earlier than females. During post-breeding migration, females took approximately 25 fewer days than males to migrate from breeding sites to molt and staging sites, and then wintering areas. Most individuals used molt sites in James and Hudson bays before migrating directly to coastal wintering sites, which took approximately 11 days and covered 1,524 km. Males tended to arrive at wintering areas 10 days earlier than females. Individuals wintering near one another did not breed closer together than expected by chance, suggesting weak spatial structuring of the Atlantic population. Females exhibited greater fidelity (4.5 km) to previously used breeding sites compared to males (60 km). A substantial number of birds bred west of Hudson Bay in the Barrenlands, suggesting this area is used more widely than believed previously. Hudson and James bays provided key habitat for black scoters that winter along the Atlantic Coast, with most individuals residing for >30% of their annual cycle in these bays. Relative to other species of sea duck along the Atlantic Coast, the Atlantic population of black scoter is more dispersed and mobile during winter but is more concentrated during migration. These results could have implications for future survey efforts designed to assess population trends of black scoters. © 2021 The Wildlife Society.     

Dietary analysis reveals differences in the prey use of two sympatric bat species

One mechanism for morphologically similar and sympatric species to avoid competition and facilitate coexistence is to feed on different prey items within different microhabitats. In the current study, we investigated and compared the diet of the two most common and similar‐sized bat species in Japan—Murina ussuriensis (Ognev, 1913) and Myotis ikonnikovi (Ognev, 1912)—to gain more knowledge about the degree of overlap in their diet and their foraging behavior. We found that both bat species consumed prey from the orders of Lepidoptera and Diptera most frequently, while the proportion of Dipterans was higher in the diet of M. ikonnikovi. Furthermore, we found a higher prey diversity in the diet of M. ikonnikovi compared to that of M. ussuriensis that might indicate that the former is a more generalist predator than the latter. In contrast, the diet of M. ussuriensis contained many Lepidopteran families. The higher probability of prey items likely captured via gleaning to occur in the diet of M. ussuriensis in contrast to M. ikonnikovi indicates that M. ussuriensis might switch between aerial‐hawking and gleaning modes of foraging behavior. We encourage further studies across various types of habitats and seasons to investigate the flexibility of the diet composition and foraging behavior of these two bat species.     

Food resource partitioning of the <Emphasis Type="Italic">Mustelus lunulatus</Emphasis> and <Emphasis Type="Italic">Mustelus henlei</Emphasis> (Elasmobranchii: Carcharhiniformes)

The feeding habits and trophic ecology of Mustelus lunulatus and Mustelus henlei in the central coast of the Colombian Pacific were evaluated and compared to determine whether there was trophic niche overlap or resource partitioning between these two sympatric shark species. A total of 59 prey items were identified and grouped into 10 taxonomic categories. Mustelus lunulatus fed in large proportion on Stomatopoda and Brachyura, whereas M. henlei fed almost exclusively on Teleostei. Dendrobranchiata, Cephalopoda, Anomura and Polychaeta complemented the diets of both species. There were significant differences in diet between the two species, and there was an ontogenetic diet shift in Mustelus lunulatus, with Stomatopoda being the main prey item of juveniles and Brachyura the main prey item of adults. Dietary overlap (by sex and size) was low between species, but it was high for each species, with significant overlap between juveniles and adults of M. lunulatus and M. henlei, and between males and females of M. henlei. There were differences in the trophic levels of the species, sexes and sizes. This study suggests there is food resource partitioning, and differing ecological function of the two Mustelus species in the food web of the study area.     

Interspecific differences in prey items in relation to morphological characteristics among four lutjanid species (Lutjanus decussatus, L. fulviflamma, L. fulvus and L. gibbus)

Clarifying interspecific differences in prey items in relation to morphological characteristics is a fundamental aspect to understand the mechanism enabling the diversity of feeding ecology of fishes. The aim of the present study was to clarify the relationship between prey items and body shape variation, teeth and mandible characteristics for four lutjanid species: Lutjanus decussatus, L. fulviflamma, L. fulvus and L. gibbus. Stomach contents analysis revealed that the main prey items of L. decussatus were fishes, L. fulviflamma were crabs and fishes, and L. fulvus and L. gibbus was crabs. Body shape analysis revealed that L. decussatus and L. fulviflamma had a shallower body depth whereas L. fulvus and L. gibbus had a deeper body depth. The two species with a shallower body had long teeth whereas the other two species with a deeper body depth had shorter teeth. The jaw-lever mechanics were compared and L. decussatus and L. fulviflamma have a faster mouth opening–closing mechanism. Canonical correspondence analysis revealed that fishes was the major prey item for the species having a shallower body depth, higher teeth length and lower ratios of in-lever to out-lever of mandibles, whereas crabs was the major prey item for the species having a deeper body depth, lower teeth length and higher ratios of in-lever to out-lever of mandibles. It is suggested that the interspecific differences in main prey items among the four species are directly related to behavioral differences based on body shape, teeth characteristics and jaw-lever mechanics.     

Distribution patterns of wintering sea ducks in relation to the North Atlantic Oscillation and local environmental characteristics

Twelve species of North American sea ducks (Tribe Mergini) winter off the eastern coast of the United States and Canada. Yet, despite their seasonal proximity to urbanized areas in this region, there is limited information on patterns of wintering sea duck habitat use. It is difficult to gather information on sea ducks because of the relative inaccessibility of their offshore locations, their high degree of mobility, and their aggregated distributions. To characterize environmental conditions that affect wintering distributions, as well as their geographic ranges, we analyzed count data on five species of sea ducks (black scoters Melanitta nigra americana, surf scoters M. perspicillata, white-winged scoters M. fusca, common eiders Somateria mollissima, and long-tailed ducks Clangula hyemalis) that were collected during the Atlantic Flyway Sea Duck Survey for ten years starting in the early 1990s. We modeled count data for each species within ten-nautical-mile linear survey segments using a zero-inflated negative binomial model that included four local-scale habitat covariates (sea surface temperature, mean bottom depth, maximum bottom slope, and a variable to indicate if the segment was in a bay or not), one broad-scale covariate (the North Atlantic Oscillation), and a temporal correlation component. Our results indicate that species distributions have strong latitudinal gradients and consistency in local habitat use. The North Atlantic Oscillation was the only environmental covariate that had a significant (but variable) effect on the expected count for all five species, suggesting that broad-scale climatic conditions may be directly or indirectly important to the distributions of wintering sea ducks. Our results provide critical information on species–habitat associations, elucidate the complicated relationship between the North Atlantic Oscillation, sea surface temperature, and local sea duck abundances, and should be useful in assessing the impacts of climate change on seabirds.     

The foraging ecology of sympatric marine fish in the genus Embiotoca (Embiotocidae): Importance of foraging behavior in prey size selection

Summary Two locally sympatric temperate marine reef fishes, Embiotoca jacksoni and E. lateralis (Embiotocidae), have high taxonomic similarity in diets. Subdivision of gammarid amphipods, their principal prey, was found. E. jacksoni took more tubicolous gammarid amphipods whereas E. lateralis consumed mostly free-living individuals. The species differed considerably with respect to between-individual variability in taxonomic compositions of their diets. Each E. jacksoni closely resembled other conspecifics in this regard while individual E. lateralis displayed very high between-fish variation. The principal interspecific difference in fish diets concerned the sizes of prey items taken. E. jacksoni ate small but very common items and the mean prey weight in their guts did not differ from random collections of available prey. E. lateralis concentrated on large, rarer sizes such that the average prey weight in their guts was much heavier than available or in the diet of E. jacksoni of the same length. Disparate foraging behaviors was a much better indicator of the relative differences in diets of these two fishes than was external fish morphology. E. jacksoni, which can winnow prey items from unwanted debris, was a relatively indiscriminant forager. E. lateralis did not winnow but actively searched for prey. This species was a much more discriminating forager, but displayed much variability in foraging behavior.     

Feeding associations between Red-necked Grebes Podiceps griseigena and Velvet Scoters Melanitta fusca in winter

Red-necked Grebes Podiceps griseigena wintering along the coast of Jseren, southwest Norway, were found to feed either solitarily or in close association with Velvet Scoters Melanitta fusca feeding on bottom prey (mainly echinoderms) dug out from the sandy substrate. By scuba diving at spots where both species were feeding, we found that stirring the sand caused polychaete worms to emerge from the substrate. Bottom samples showed that these worms (on average >1000 per m²) vastly outnumbered other animal taxa living in the substrate and that polychaetes were probably the most likely prey of grebes associated with scoters. Food competition between the two species and/or kleptoparasitism by the grebes were probably not involved (no food-stealing attempts by the grebes toward scoters handling prey brought to the surface, no aggression by scoters toward grebes and no effect of the grebes on the time budget of the scoters). Red-necked Grebes associating with scoters were mainly first-year birds, and the frequency of association decreased from a maximum of nearly 60% of the grebes in November to c. 5% before spring departure in April. Grebes feeding solitarily hunted in a manner resembling divers (Gavia) , and they brought fish to the surface significantly more often than grebes feeding with scoters. Solitary grebes spent less time feeding and more time preening and swimming than did grebes associating with scoters. The association appears to be a way naive birds could easily obtain prey. Skills needed to dive for more nutritious but agile fish are probably gradually acquired through the winter as more of the grebes adopt solitary feeding.     

Gutsy genetics: identification of digested piscine prey items in the stomach contents of sympatric native and introduced warmwater catfishes via DNA barcoding

A major focus of ecology is understanding trophic relationships and energy flows in natural systems, associated food web dynamics and changes in food webs due to introduced species. Predator-prey interactions are often assessed by examining stomach contents. However, partially digested remains may be difficult to accurately identify by traditional visual analysis. Here we evaluate the effectiveness of DNA barcoding to identify digested piscine prey remains in invasive Blue Catfish Ictalurus furcatus, non-native, but established Channel Catfish Ictalurus punctatus and native White Catfish Ameiurus catus from Chesapeake Bay, USA. Stomach contents were examined and piscine prey items were scored as lightly digested, moderately digested or severely digested. A 652 base pair region of the cytochrome c oxidase subunit I (COI-5P) mitochondrial DNA gene was sequenced for each prey item. Edited barcode sequences were compared to locally-caught and validated reference sequences in BOLD (Barcode of Life Database). A large majority of prey items were sufficiently digested to limit morphological identification (9.4 % to species and an additional 12.1 % to family). However, overall barcoding success was high (90.3 %) with little difference among the digestion classifications. Combining morphological and genetic identifications, we classified 91.6 % of fish prey items to species. Twenty-three fish species were identified, including species undergoing active restoration efforts (e.g., Alosa spp.) and commercially important species, e.g., Striped Bass Morone saxatilis, White Perch Morone americana, American Eel Anguilla rostrata and Menhaden Brevoortia tyrannus. We found DNA barcoding highly successful at identifying all but the most heavily degraded prey items and to be an efficient and effective method for obtaining diet information to strengthen the resolution of trophic analyses including diet comparisons among sympatric native and non-native predators.     

Prey selection and foraging period of the predaceous rocky intertidal snail,Acanthina punctulata

Summary The diet and foraging period of the neogastropod Acanthina punctulata were investigated in order to test various aspects of recent optimal foraging strategy models. This intertidal snail is an actively searching predator which preys on snails and barnacles by boring a hole in the shell and rasping out the flesh. Unlike many gastropod predators, Acanthina drill its gastropod prey at a very specific location on the columella, the thickest portion of the shell. Acanthina's foraging period can be interpreted as a compromise between maximizing the energy obtained by feeding and minimizing risk of mortality from exposure to wave action. That foraging period minimizing risk of being dislodged by waves appears to be during low tide when the predators can be in shallow pools. However, prey cannot be captured and consumed during one low tide. Thus Acanthina must be exposed during some high tides, and its strategy appears to be to restrict movement while exposed. Thus search is not initiated during high tide, but drilling and prey consumption are continued during that time. A snail not drilling or consuming prey seeks the protection of crevices or large anemones during high tide. A model is presented to indicate the relative amounts of risk and net energy for Acanthina at successive low and high tides. Predictions from the model, e.g., minimizing search time to avoid being exposed for an additional high tide and no movement during high tide are supported by field data. Acanthina commences foraging at the beginning of low tide, searches initially for preferred prey, but if unsuccessful, settles for a less preferred prey and begins drilling this prey before the end of low tide. Drilling and ingestion of prey occur during the following high and sometimes low tides. These handling times take 95% of the total foraging time in the field, while search time takes only 5% (pursuit time is negligible). Drilling alone accounts for 48–70% of the total drilling and eating time. In the laboratory, drilling and eating time for littorine food ranged from 15–60 hrs per item. The time to drill and eat a littorine increases exponentially with prey length. Since handling and processing prey items represents such a large investment of time, Acanthina would be expected to be very selective with respect to choice of prey items. Electivity coefficients from field data suggest that littorines are preferred over barnacles. Acanthina in the laboratory optimizes the amount of biomass ingested per time by choosing larger littorines over smaller ones and by preferring the more readily drilled species.It is suggested that Acanthina obtains information about the range of prey available initially by encountering and evaluating quite a few prey before making a selection, but usually by comparing an item of prey encountered to the prey it recently ingested. This latter method should provide a basis for evaluating prey encountered and has the advantage of reducing search time, the total amount of time spent feeding and thus the high-tide time exposed to wave action.In a similar manner, the decrease in the level of acceptability of prey as search time increases represents a compromise between maximizing energy obtained and minimizing risk from mortality.     

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 δ¹⁵N was demonstrated. Pleuragramma antarcticum trophic level was estimated as 3·7 (postlarval fish) and 4·1 (fish aged 3+ years).     

Common Buzzards wintering strategies as an effect of weather conditions and geographic barriers

AimMigration is a constantly changing adaptation due to the climate condition evolution. The struggle for surviving during harsh winter season is different across Europe, being more complex toward the inner parts of the continent. The current approach explores the Common Buzzard number variation during the cold season and the climatic predictors of birds of prey wintering movements in relation to the possible influences of the Carpathian Mountains, which may act as a geographical barrier providing shelter from cold air outbreak from north and northeast of the continent.LocationRomania (45°N25°E).TaxonBirds of Prey.MethodsWe applied a GLMM to investigate the relation between continental and local climatic factors with the number of Common Buzzard observations in two regions. The first region is located inside the Carpathian Arch and the other one outside, east of this large mountains chain.ResultsThe Common Buzzard numbers wintering Eastern from the Carpathian Mountains are highly influenced by AO (Z = 2.87, p < .05%), while those wintering western are influenced by NAO (Z = 2.17, p < .05%). This is the first proof of separating influences for biodiversity of AO and NAO at continental scale, outlining the influence limit placed over the Eastern Carpathian Mountains.Main conclusionsThe Carpathian Mountains act like a geographic barrier, separating the wintering Common Buzzard populations from both sides of the mountain range. While the high number of individuals in Moldova is related to their eastern and northeastern Europe origins, in Transylvania the large number of individuals observed is related to the more sheltered characteristics of the region attracting individuals from central Europe. Also, since Transylvania region is well sheltered during cold air outbreak, it represents a more favorable region for wintering. From this point of view, we can consider that the Carpathian Mountains are a geographic barrier for wintering birds of prey.     

Taxonomy and Distribution of Freshwater Pearl Mussels (Unionoida: Margaritiferidae) of the Russian Far East

The freshwater pearl mussel family Margaritiferidae includes 13 extant species, which are all listed by IUCN as endangered or vulnerable taxa. In this study, an extensive spatial sampling of Margaritifera spp. across the Russian Far East (Amur Basin, Kamchatka Peninsula, Kurile Archipelago and Sakhalin Island) was conducted for a revision of their taxonomy and distribution ranges. Based on their DNA sequences, shell and soft tissue morphology, three valid species were identified: Margaritifera dahurica (Middendorff, 1850), M. laevis (Haas, 1910) and M. middendorffi (Rosén, 1926). M. dahurica ranges across the Amur basin and some of the nearest river systems. M. laevis is distributed in Japan, Sakhalin Island and the Kurile Archipelago. M. middendorffi was previously considered an endemic species of the Kamchatka. However, it is widespread in the rivers of Kamchatka, Sakhalin Island, the Kurile Islands (across the Bussol Strait, which is the most significant biogeographical boundary within the archipelago), and, likely, in Japan. The Japanese species M. togakushiensis Kondo & Kobayashi, 2005 seems to be conspecific with M. middendorffi because of similar morphological patterns, small shell size (<100 mm long) and overlapped ranges, but it is in need of a separate revision. Phylogenetic analysis reveals that two NW Pacific margaritiferid species, M. laevis and M. middendorffi, formed a monophyletic 18S rDNA clade together with the North American species M. marrianae and M. falcata. The patterns that were found in these Margaritifera spp. are similar to those of freshwater fishes, indicating multiple colonizations of Eastern Asia by different mitochondrial lineages, including an ancient Beringian exchange between freshwater faunas across the Pacific.     

Diving behaviour and diet of the blue-eyed shag at South Georgia

Summary This paper describes a concurrent investigation of individual variation in diet, diving patterns and performance of blue-eyed shags Phalacrocorax atriceps breeding at South Georgia. Within one day individual shags exhibited one of three foraging strategies: short diving (4 birds, all dives 120 s) and mixed diving (15 birds, predominantly long but with a few short dives). The mean number of dives per day was significantly higher in shags that only made short dives (mean=172.0, SE=43.2) than birds with a mixed diving strategy (mean=40.5, SE=4.7) and birds that made only long dives (mean=30.8, SE=1.8). Diet was assessed using hard remains recovered from pellets regurgitated by the shags. Small nototheniid fish (c. 10 kJ per item) were by far the commonest prey but most pellets contained additional items. The frequency of pellets with additional items of higher energy value than nototheniid fish (10.c. 900 kJ per item), lower energy value (>1–10 kJ per item) and both higher and lower energy items was strikingly similar to the frequency of shags making long, short and both long and short dives respectively. Predicted aerobic dive limits suggested that during long dives, blue-eyed shags were probably sustained by anaerobic metabolism. Models of prey capture rates demonstrated that for both long and short diving, many items must be caught per dive when birds are feeding on prey at the lower end of the energy range. Predicted capture rates for the commonest recorded prey (small fish) differ markedly between the two diving strategies.     

Food habits, occurrence, and population structure of the bat ray, Myliobatis californica, in Humboldt Bay, California

The bat ray, Myliobatis californica, is the most common, large predatory fish in Humboldt Bay, California. To prevent bat ray predation on cultured oyster beds, much effort has focused on reducing their population. A 13 month study was conducted in Humboldt Bay to examine the rays' use of the bay, population structure, and feeding ecology. Bat rays are seasonally found in Humboldt Bay during the spring, summer, and early fall months. Adult rays were most abundant during the summer months, while numbers of juveniles increased through the summer and early fall, indicating that Humboldt Bay is an important pupping and nursery ground. Very few rays were found in the bay during the colder months of the year. This decline in abundance is attributed to cooler water temperatures (< 10° C). The stomach contents from 503 bat rays were examined. Overall, clams were the predominant prey item. The index of importance and Shannon-Weiner diversity index indicated that food habits of bat rays change with increasing size. Larger prey items and a wider variety of prey items were consumed as rays increased in size. Dietary importance of small clams and Crangon shrimp decreased with increasing ray size, while the importance of larger prey items (e.g. large clams, Cancer crabs, blue mud shrimp, echiuran worms) increased. Predation on oysters was rare. Differences between the diets of male and female rays of similar sizes were also observed.     

Diet of the Long-eared Owl,Asio otus,in Central Anatolia (Aves: Strigidae)

In a one-year study on the diet of the Long-eared Owl, Asio otus, in the area of Karap?nar in Central Anatolia, 5324 prey items were recovered from 3314 pellets collected at monthly intervals. At least 7 species of mammals belonging to Insectivora (Crocidura suaveolens) and Rodentia (Allactaga williamsi, Cricetulus migratorius, Meriones tristrami, Mescocricetus brandti, Microtus guentheri, M. sp., Mus macedonicus) were identified. Rodentia were dominant and contributed 93.8% of the number of prey items of the Long-eared Owl. Microtus guentheri accounted for 83.9% of the rodent remains. The diet pattern was more diverse in summer, when some 24% of the diet consisted of non-mammal prey items (birds, insects).     

长江口中国花鲈食性分析

中国花鲈(Lateolabrax maculatus)是长江口重要的经济鱼类之一。根据2010年7月至10月在长江口崇明东滩团结沙和东旺沙水域采集到的胃含物样品,对中国花鲈的摄食习性进行了研究。结果表明,从中国花鲈胃含物中共鉴定出6类27种饵料生物,其多样性指数H’值为2.484,均匀度指数J’为0.7535,优势指数D为0.1262。采用百分比相对重要性指数(IRI%)和综合指标优势指数(Ip)分析的结果较一致,鱼类是长江口中国花鲈夏季主要食物,其百分比相对重要性指数(IRI%)和综合指标优势指数(Ip)分别为82.63%和94.48,鮻(Liza haematocheila)为优势饵料生物(IRI%=41.89,Ip=53.20)。团结沙和东旺沙中国花鲈食性差异较大,主成分分析(PCA)表明鲚属(Coilia spp.)、舌虾虎鱼(Glossogobius giuris)、脊尾白虾(Exopalaemoncarinicauda)和雷伊著名团水虱(Gnorimosphaeroma rayi)是造成这种差异的主要饵料生物种类。     

Gape-limitation,foraging tactics and prey size selectivity of two microcarnivorous species of fish

Summary Patterns of prey size selectivity were quantified in the field for two species of marine microcarnivorous fish, Embiotoca jacksoni and Embiotoca lateralis (Embiotocidae) to test Scott and Murdoch's (1983) size spectrum hypothesis. Two mechanisms accounted for observed selectivity: the relative size of a fish in relation to its prey, and the type of foraging behavior used. Juvenile E. jacksoni were gape limited and newborn individuals achieved highest selectivity for the smallest prey size by using a visual picking foraging strategy. As young E. jacksoni grew, highest preference shifted to the next larger prey sizes. When E. jacksoni reached adulthood, the principal mode of foraging changed from visual picking to relatively indiscriminant winnowing behavior. The shift in foraging behavior by adults was accompanied by a decline in overall preference for prey size; sizes were taken nearly in proportion to their relative abundance. Adult E. lateralis retained a visual picking strategy and achieved highest selectivity for the largest class of prey. These differences in selectivity patterns by adult fish were not explained by gape-limination since adults of both species could ingest the largest prey items available to them. These results support Scott and Murdoch's (1983) hypothesis that the qualitative pattern of size selectivity depends largely on the range of available prey sizes relative to that a predator can effectively harvest.