Proportion Of Invertebrates Research Articles

Mercury contamination is an invisible threat to declining migratory shorebirds along the East Asian-Australasian Flyway

Exposure to pollutants is a potentially crucial but overlooked driver of population declines in shorebirds along the East Asian-Australasian Flyway. We combined knowledge of moult strategy and life history with a standardised sampling protocol to assess mercury (Hg) contamination in 984 individuals across 33 migratory shorebird species on an intercontinental scale. Over one-third of the samples exceeded toxicity benchmarks. Feather Hg was best explained by moulting region, while habitat preference (coastal obligate vs. non-coastal obligate), the proportion of invertebrates in the diet and foraging stratum (foraging mostly on the surface vs. at depth) also contributed, but were less pronounced. Feather Hg was substantially higher in South China (Mai Po and Leizhou), Australia and the Yellow Sea than in temperate and Arctic breeding ranges. Non-coastal obligate species (Tringa genus) frequently encountered in freshwater habitats were at the highest risk. It is important to continue and expand biomonitoring research to assess how other pollutants might impact shorebirds.

Effects of food availability on the trophic niche of the hazel dormouse Muscardinus avellanarius

The scale at which variations in food availability affect the foraging habits of individual animals can determine how the distribution of food resources affects populations. For species of conservation concern, these factors can have important implications for the management of habitats, as spatial and temporal variations in resource availability influence the trophic ecology of both individuals and populations. The hazel dormouse Muscardinus avellanarius is a species with seasonal dietary shifts and limited ranging, and whose populations in Great Britain are exhibiting marked decline, despite conservation measures. We compared resource availability and variation in dormouse traits with their trophic characteristics, determined by stable isotope analysis of dormouse hair and of their putative food items.The trophic levels of individual dormice were associated with the abundance of invertebrates in the surrounding habitat and in the woodland as a whole. Assessment of dormouse dietary composition suggests that the proportions of invertebrates and of tree seeds and flowers in dormouse diets are affected by the abundance of food plants in the local habitat. This suggests that dormice can exploit both invertebrates and plants in proportion to their availability, and are variable in their predatory habits, in response to both the availability of invertebrates and plants.Dormouse populations exhibit a broader trophic niche in autumn than in spring, most likely a consequence of their consumption of foods derived from a wider variety of tree and shrub species. We found no relationship between isotope signatures or food availability and the body mass or torpor of individuals, or the status of populations. This may be because, on the sites we studied, dormice could adapt to different food availabilities without discernible individual and population effects.Dormice are opportunistic feeders, rather than specialists, making use of abundant food resources at a local scale. Habitat conservation for dormice, therefore, could benefit from establishing and maintaining habitats that increase the overall abundance and uniform distribution of both flower and fruit-bearing shrubs and trees and invertebrate populations, at a fine spatial scale.

Decadal variations in the community status of economically important invertebrates in the Bohai Sea

With the decline of fish stocks, the proportions of economically important invertebrates like crustaceans and cephalopods have increased in the Bohai Sea. The community structure and trophic level of economically important invertebrates were analyzed using the bottom trawl survey data collected by the Yellow Sea Fisheries Research Institute in the Bohai Sea in May and August of 1958–1959, 1982, 1992–1993, 2004, 2009 and 2015. A total of 37 species of economically important invertebrates, belonging to 5 orders, 24 families, were captured. The biomass densities of economically important invertebrates in the Bohai Sea displayed an overall downward trend from 1982 to 2015. Oratosquilla oratoria and Loligo spp. were the most dominant species in the past 30 years, the biomass proportion of O. oratoria increased gradually in both May and August from 1982 to 2015. Moreover, biodiversity indices of economically important invertebrates in the Bohai Sea appeared to decline from 1982 to 2004 and then increased in 2015. Similarly, the mean trophic level of economically important invertebrates declined from 1982 to 2004 and increased slightly in 2015. Overall, although the proportions of invertebrates have increased, the biomass densities in the Bohai Sea have displayed an overall downward trend from 1982 to 2015. The increases in the biodiversity and trophic level of economically important invertebrates after the 2000s, possibly benefit from stock enhancement projects implemented by governments at different levels and national fishery management measures such as the “double-control” of the total number and engine power of fishing vessels and summer moratorium of fishing.

Metal contamination and food web changes alter exposure to upper trophic levels in upper Blackfoot River basin streams, Montana

Reduced invertebrate abundance and diversity are common responses to metals contamination in mining-impacted streams. The resulting changes in community composition may have implications for metals accumulation and transfer through the food web. We investigated how changes in invertebrate community composition (abundance, species richness, and food web complexity) influence metals bioaccumulation and exposure risk to upper trophic levels along a contamination gradient in the upper Blackfoot River Basin, Montana. Invertebrate species richness exhibited the strongest decline with increasing sediment metals concentrations, driven by the loss of metals-sensitive taxa. These changes in invertebrate community composition resulted in a decline in the proportion of invertebrates in the scraper functional feeding group, likely influencing dietary metals exposure to the invertebrate community. Additionally, invertebrates with a strong propensity-to-drift increased with sediment contamination, potentially facilitating metals transfer to fish and higher trophic levels through predation. Using invertebrate exposure values (invertebrate abundance × metals concentrations), we found that moderately contaminated sites in our study area produced both the highest invertebrate exposure values and the highest fish tissue metals concentrations. Considering both changes in invertebrate community composition and metal concentrations is an important step towards understanding and evaluating potential toxic effects to upper trophic levels in mining-impacted streams.

Intra-Seasonal and Brood-Size Dependent Variation in the Diet of Black Stork (Ciconia nigra) Nestlings

Nestling diet and parental provisioning rate are important determinants of reproductive success and future offspring performance in birds. The diet of Black Stork (Ciconia nigra) nestlings was characterized and tested for intra-seasonal and brood-size dependent variation in the type and mass of prey provisioned to the brood. Data were collected on 576 prey items from 45 Black Stork broods in central Poland during 2005–2016. Black Stork nestlings were provisioned almost exclusively with fish and amphibians; the proportion of invertebrates in their diet was marginal. Fish were a dominant component of nestling diet, comprising up to 65% of prey items and over 85% of total prey mass. Common spadefoot tadpoles (Pelobates fuscus), weatherfish (Misgurnus fossilis) and Prussian carp (Carassius gibelio) were among the most abundant prey. Black Storks foraged on relatively small prey, with an average length of 101.4 ± 1.5 mm (n = 576) and an average mass of 13.8 ± 1.0 g (n = 550). Larger broods were significantly more often fed with amphibians and with lighter prey. As the season progressed, the probability of preying on amphibians increased. This study provides evidence for Black Stork provisioning effort optimization mediated by selection of smaller, but easier to catch and handle prey, such as common spadefoot tadpoles.

Increased Water Pollution After Closure of Australia’s Longest Operating Underground Coal Mine: a 13-Month Study of Mine Drainage, Water Chemistry and River Ecology

This study investigated the water pollution impact of mine drainage from an underground colliery that had stopped mining 3 years earlier. After more than a century of operation, the mining stopped, pumping ceased and groundwater accumulated, causing the flooding of the deepest sections (c. 15%) of the mine workings. The mine then began free-draining to the adjacent Wingecarribee River. The closure and flooding triggered acid mine drainage that has resulted in mildly acidic pH and higher concentrations of several metals. Of greatest environmental concern were ecologically hazardous concentrations of three metals: nickel (418 μg/L), zinc (1161 μg/L) and manganese (11,909 μg/L) in the mine drainage. Such concentrations are some of the highest concentrations reported for these metals in drainage from an Australian coal mine and are 2.5 to seven times higher than when the mine was operating. The concentration of nickel and manganese were stable, but zinc gradually declined throughout the 13-month study. The inflow of the drainage increased the concentration of the three metals in the river, causing exceedance of water quality guidelines for protection of aquatic species. The ecological impact of the mine drainage was substantial, causing a 63% reduction in family richness and a 90% reduction in proportion of invertebrates from the known pollution-sensitive orders (Ephemeroptera, Plecoptera and Trichoptera). Literature suggests the pollution could continue for decades. Of additional concern is that the mine drainage is currently untreated and pollutes a river in the water catchment of Australia’s largest domestic water supply reservoir.

Species traits reveal effects of land use, season and habitat on the potential subsidy of stream invertebrates to terrestrial food webs

Adult aquatic insects with a terrestrial life-stage are important vectors transferring resources assimilated in freshwater environments to terrestrial consumers. Research on this linkage has focused particularly on how terrestrial environmental features affect dispersal of adult aquatic insects, and on the responses of terrestrial consumers. However, both the timing and extent of dispersal by adult aquatic insects are further regulated by their species-specific life history traits. We sampled aquatic invertebrates from nine streams in central Sweden, and assessed how the composition of key traits related to dispersal and life history varied between in-stream habitats (riffles, pools), seasons (autumn, spring), and among streams differing in catchment land use (forested, agriculture). Traits indicative of more limited adult dispersal (e.g. small adult size and weak flying strength), along with traits indicative of strongly pulsed peaks in emergence (e.g. univoltinism and well-synchronised emergence) were all more abundant in the agricultural than forested streams in the autumn. However, these differences had disappeared by late spring, possibly reflecting early emergence by the univoltine taxa that dominated the agricultural stream communities and/or elevated mortality in the agricultural streams. Riffles supported higher abundances of insects with strongly flying adults, whereas traits associated with more limited dispersal were characteristic of insect assemblages in pools, which also supported the highest proportion of invertebrates completely lacking an adult flying stage. This result is likely to have implications at larger scales, given the dominance of soft-bottomed pool habitats and scarcity of riffles in many agricultural landscapes. Overall, our analysis indicates that while overall production of aquatic invertebrates with a winged adult was greater in agricultural streams, availability of this productivity for terrestrial consumers is more likely to be spatially restricted closer to the stream channel, and potentially also more temporally pulsed .

Population variation in the trophic niche of the Trinidadian guppy from different predation regimes

Population variation in trophic niche is widespread among organisms and is of increasing interest given its role in both speciation and adaptation to changing environments. Trinidadian guppies (Poecilia reticulata) inhabiting stream reaches with different predation regimes have rapidly evolved divergent life history traits. Here, we investigated the effects of both predation and resource availability on guppy trophic niches by evaluating their gut contents, resource standing stocks, and δ15N and δ13C stable isotopes across five streams during the wet season. We found that guppies from low predation (LP) sites had a consistently higher trophic position and proportion of invertebrates in their guts and assimilate less epilithon than guppies from high predation (HP) sites. Higher trophic position was also associated with lower benthic invertebrate availability. Our results suggest that LP guppies could be more efficient invertebrate consumers, possibly as an evolutionary response to greater intraspecific competition for higher quality food. This may be intensified by seasonality, as wet season conditions can alter resource availability, feeding rates, and the intensity of intraspecific competition. Understanding how guppy diets vary among communities is critical to elucidating the role of niche shifts in mediating the link between environmental change and the evolution of life histories.

Contrasting Population and Diet Influences on Gut Length of an Omnivorous Tropical Fish, the Trinidadian Guppy (Poecilia reticulata).

Phenotypic plasticity is advantageous for organisms that live in variable environments. The digestive system is particularly plastic, responding to changes in diet. Gut length is the result of a trade-off between maximum nutrient absorption and minimum cost for its maintenance and it can be influenced by diet and by evolutionary history. We assessed variation in gut length of Trinidadian guppies (Poecilia reticulata) as a function of diet, season, ontogeny, and local adaptation. Populations of guppies adapted to different predation levels have evolved different life history traits and have different diets. We sampled guppies from sites with low (LP) and high predation (HP) pressure in the Aripo and Guanapo Rivers in Trinidad. We collected fish during both the dry and wet season and assessed their diet and gut length. During the dry season, guppies from HP sites fed mostly on invertebrates, while guppies in the LP sites fed mainly on detritus. During the wet season, the diet of LP and HP populations became very similar. We did not find strong evidence of an ontogenetic diet shift. Gut length was negatively correlated with the proportion of invertebrates in diet across fish from all sites, supporting the hypothesis that guppy digestive systems adapt in length to changes in diet. Population of origin also had an effect on gut length, as HP and LP fish maintained different gut lengths even in the wet season, when their diets were very similar and individuals in both types of populations fed mostly on detritus. Thus, both environment and population of origin influenced guppies gut length, but population of origin seemed to have a stronger effect. Our study also showed that, even in omnivorous fish, gut length adapted to different diets, being more evident when the magnitude of difference between animal and plant material in the diet was very large.

Food Composition and Prey Selection of Cod, <I>Gadus Morhua</I> (Actinopterygii: Gadiformes: Gadidae), in the Southern Baltic Sea

Background. At the end of 1980s, ecological regime shifts occurred in the Baltic. Since, the Baltic fish assemblage has been dominated by sprats, whereas before cod was the dominant fish species. The majority of previous food studies refer to the period before the shift. This raises the question, how changes in the Baltic ecosystem have affected the diet of cod. The aim of the presently reported study was to identify the differences in the food composition of cod depending on the area, depth, season, and the cod size and compare it with the findings from the 1970s and 1980s. Materials and methods. Food composition and selection of prey size for Baltic cod was evaluated by examining the stomach contents of 556 adult cod, collected in 2006 and 2007. Fish stomachs were sampled from research catches within the Polish Exclusive Economic Zone. Results. The main component of the cod diet were the clupeids, constituting more than 67% of the total weight of the food recovered from the specimens studied. Other fishes in the diet represented Gobiidae, Ammodytidae, as well as young cod. The dominant invertebrate in the diet was the isopod Saduria entomon which accounted for 13% of the diet by weight. The weight proportion of larger fish, such as herring, Clupea harengus (L.), and cod, increased with the cod size, while the proportion of small- and medium-sized fish (sprats, gobies) decreased. The food composition of cod varied seasonally. The weight proportion of European sprat, Sprattus sprattus (L.), was much higher in winter (55%) than in fall (27%), while the proportion of cod in the diet was higher in the fall (10%) than in winter (4%). The proportion of sprat in the diet increased with depth, while that of Ammodytidae and Gobiidae showed a decreasing trend. At depths greater than 40 m, the proportion of invertebrates in cod stomachs decreased. This study demonstrated a significant area effect for sprat; year effect for sprat and Saduria entomon; a seasonal effect for young cod and S. entomon; and a depth effect for sprat, young cod, and S. entomon. The occurrences of herring and small cod increased in the stomach as the predator increased, while no significant relation was found for sprat and S. entomon. The data collected do not indicate that cod select a specific size of sprat or herring, though cod were found to use size selection for S. entomon and juvenile cod. Conclusion. The food composition of cod has undergone certain changes compared to results of Załachowski (1977, 1985), which covered the 1970s and 1980s. Currently, the proportion of clupeids in the food is approximately 67% (in weight), while during the 1977–1982 it was in the range of 25%–50% depending on cod length. In 2006 and 2007 sprat was the main cod diet component rather than herring.

Body mass, phylogeny and diet composition affects kidney morphology in passerine birds

We studied the renal morphology of 16 species of passerines to assess whether the composition of the diet of birds have been paralleled by differences in the characteristics of the kidneys. We determined the number and length of the medullary cones and the percentage of renal medulla in birds with contrasting dietary habits and then correlated these features with the percentage of nitrogen and proportion of invertebrates in the diet. To examine the correlation between kidney and diet variables, we first used standard correlation and least square regression, and correlation and regression on phylogenetically independent data. We found that the mass of the medullary portion of the kidney, and the medullary cone length were negatively correlated with the percentage of invertebrates present in the diet. We hypothesized that the further development of the renal medulla observed in granivorous birds may be correlated with the small amount of water present in the seeds. Our results suggest that the availability of water in different foods is probably one of the main factors that have led to structural and probably functional changes of the kidney in the studied species.

Feeding Ecology and Development of Juvenile Black Ducks in Maine

Feeding Ecology and Development of Juvenile Black Ducks in Maine

Feeding ecology of a nesting population of the Common Buzzard (Buteo buteo) in the Upper Nitra Region, Central Slovakia

Feeding ecology of a nesting population of the Common Buzzard (Buteo buteo) in the Upper Nitra Region, Central Slovakia During routine checks of the nests of the Common Buzzard in the Upper Nitra region (Central Slovakia) we collected food remains and recorded all prey given to the nestlings. We present results from the period 2006-2008. 606 food items were determined, comprising mainly mammals (67%). Birds were also frequent (17%), less so amphibians and reptiles (7%) and invertebrates (10%). During the rodent population peak in 2007, Buzzard pairs nesting in the valley preyed mainly on Microtus arvalis, whereas pairs living at the rim of the valley fed on Myodes glareolus and Talpa europaea, and higher in the Vtáčnik Mts birds fed on Apodemus flavicollis. After a massive decline in the rodent population in the following year 2008, the survival rate of the nestlings was very low and the proportion of invertebrates in their diet increased. Birds that were most frequently preyed upon included juvenile Turdus philomelos and Garrulus glandarius, prey identified from amphibian was mainly Bufo bufo, and from reptile prey was largely Anguis fragilis.

A comparison of natural and created depressional wetlands in central Oklahoma using metrics from indices of biological integrity

Created wetlands and water bodies that have wetland characteristics (old farm ponds) appear to provide many of the habitat attributes of natural systems. To compare the biological and physical characteristics of natural and created wetlands, we evaluated water chemistry and a suite of metrics associated with the plant, macroinvertebrate, and avian assemblages at 12 natural and six created systems in central Oklahoma. The natural wetlands had significantly shallower depths and higher turbidity levels than the created wetlands. Of 43 metrics across the three biotic assemblages, seven were significantly different between the two wetland types. The proportions of hemipteran insects from the family Corixidae and insectivorous bird species were both greater in natural than created wetlands. The proportion of perennial plant species, the proportion of invertebrates in the shredder feeding guild, the number of Ephemeroptera, Trichoptera, Sphaeridae, and dragonfly (ETSD) taxa, the proportion of individuals in the dominant bird taxa, and the proportion of avian edge species were all greater in created wetlands than in natural wetlands. The community similarity (based on Jaccard’s similarity index) in the two wetland types was 38% for plants, 56% for macroinvertebrates, and 65% for birds. For some individual metrics, assemblage members had similar attributes (e.g., proportion of omnivorous taxa) although the specific taxa often differed between natural and created wetlands. These differences may influence the performance of certain assessment methods when they are applied to created wetlands.

Fluctuations in chick diet of the Squacco Heron Ardeola ralloides in southern France: changes over the last 30 years

Capsule The composition varied between colony site, month and year. Aims To determine the diet composition of chicks and its variations in 2000 and 2001. To look for any changes over the last 30 years. Methods Chick regurgitates were analysed to determine which Order contributed most to the diet, by frequency and by biomass. Results During 2000 and 2001 chick diet was dominated by insects (92% and 70% by biomass, respectively), mainly Coleoptera (60% and 41%) and Orthoptera (27% in both years). The dry mass of Orthoptera, Coleoptera adults, Odonata and amphibians differed significantly between breeding sites, months and years.The proportion of invertebrates (in biomass) increased from 36.5% in 1970 and 31% in 1971 to 95% in 2000 and 90% in 2001 whereas the proportion of amphibians decreased in the same time from 49% and 33% in 1970 and 1971 to 5.0% and 9.5% in 2000 and 2001, respectively. Conclusion The proportion of prey types differed bewteen colony sites and months. Major changes were found in the diet composition between the early 1970s and 2000s. The possible hypotheses for the observed differences are discussed.

Spatial and temporal variation in the diet of Marbled Teal Marmaronetta angustirostris in the western Mediterranean

CapsuleThis globally threatened species is less dependent on invertebrates and more dependent on seeds than other ducks. Aims To assess seasonal variation in Marbled Teal diet at two of the most important wetlands for the west Mediterranean population. Methods Faecal samples from El Hotba, Morocco (19 in October, 28 in May) and Veta la Palma, Doñana (19 in August, five from July broods) were analysed. Gut contents of six birds from Veta la Palma (September–October) were analysed. Results At El Hotba, small seeds (especially Ruppia) and green plant material (especially charophytes) were the dominant faecal components in May and October. The proportion of invertebrates did not change, but more Corixidae and less Chironomidae were consumed in May. At Veta la Palma, Ruppia seeds were dominant in August, but Ephydridae, Chironomidae, Coleoptera and other insects were dominant in faeces from July broods. Significantly fewer Coleoptera but more Foraminifera were recorded in August. The overall proportion of invertebrates at El Hotba in May and October was higher than at Veta la Palma in August, but lower than in July broods. Corixidae were dominant in May, Ephydridae in July broods, unidentified insects, Ostracoda and Foraminifera in August and Coleoptera in October. Gut contents from Veta la Palma confirmed the dominance of Ruppia seeds in the post-breeding diet. Conclusion Marbled Teal differs in its ecology from the better-known north-temperate ducks. With the exception of ducklings, they are less dependent on invertebrates and rely on small seeds more than north-temperate ducks.

Review of Factors Affecting the Distribution and Abundance of Waterfowl in Shallow-Water Habitats of Chesapeake Bay

Long-term trends of waterfowl populations in Chesapeake Bay demonstrate the importance of shallow-water habitats for waterfowl species. Although recent increases in field feeding by geese and swans lessened the importance of shallow-water areas for these species, most duck species depend almost exclusively on shallow-water habitats. Many factors influenced the distribution and abundance of waterfowl in shallow-water habitats. Habitat degradation resulted in the decline in numbers of most duck species and a change in distribution of some species. Increased numbers of mallards (Anas platyrhynchos) in recent decades probably resulted from release programs conducted by the Maryland Department of Natural Resources and private individuals. Studies of food habits since 1885 showed a decline in submerged-aquatic vegetation in the diet of some species, such as the canvasback (Aythya valisineria), and an increase in the proportions of invertebrates in the diet. Diversity of food organisms for many waterfowl species has declined. Surveys of vegetation and invertebrates in the Chesapeake Bay generally reflect a degradation of shallow-water habitat. Human population increases in the Chesapeake Bay watershed directly and indirectly affected waterfowl distribution and abundance. The increase of exotic plant and invertebrate species in the bay, in most cases, benefited waterfowl populations. Increased contaminants have reduced the quality and quantity of habitat, although serious attempts to reverse this trend are underway. The use of shallow-water habitats by humans for fishing, hunting, boating, and other recreational and commercial uses reduced the use of shallow-water habitats by waterfowl. Humans can lessen the adverse influences on the valuable shallow-water habitats by restricting human population growth near these habitats and improving the water quality of the bay tributaries. Other affirmative actions that will improve these areas for waterfowl include greater restrictions on boat traffic in shallow-water habitats and establishing more sanctuaries in shallow-water areas that have complete protection from human disturbance. *** DIRECT SUPPORT *** A01BY074 00013

Food selection by capercaillie chicks in southern Norway

Food selection by capercaillie (Tetrao urogallus) chicks was studied using human-imprinted chicks. Invertebrates made up more than 50% of the chicks' diet during the 1st week. Feeding on plants increased to approximately 100% in 7-week-old chicks. Berries of Vaccinium myrtillus made up 85% of the plant material eaten. Berries were eaten once they ripened. Other important plant foods were flowers of Erica tetralix and Melampyrum pratense. Ants (Formicidae) were the most utilized invertebrate food. The observed decrease in the proportion of invertebrates in the diet with increasing age was not a result of decreasing invertebrate abundance. Sweep net samples showed significantly fewer invertebrates when chicks were 1 – 3 weeks old than when chicks were 4 – 6 weeks old.

Feeding Ecology of Ring-Necked Ducks in Northwestern Minnesota

Feeding ecology of ring-necked ducks (Aythya collaris) was studied in northwestern Minnesota, from April to August 1978-80. Adult male and female diets were similar throughout reproduction. Food use by adult birds before recrudescence of female gonadal tissue varied by habitat: diets for birds using temporary wetlands were dominated by plant material, whereas animal foods made up one-half of the diet of males and females collected on semipermanent and permanent wetlands later used for nesting. The proportion of invertebrates consumed by adult birds increased after the arrival period. Female reproductive protein requirements are drawn primarily from the diet during prelaying and laying. Based on estimated consumption rates, females may feed up to 19 hours/day to obtain required protein. Consumption of invertebrates by nonlaying birds suggests that their use can be energetically profitable; however, food selection by prelaying/laying hens on a noncaloric basis (e.g., minerals) may result in expenditure of fat reserves. Juveniles ate mostly invertebrates, but the proportion of animal material in the diet differed between ageclasses. Although significant food preferences were exhibited by adults and juveniles, availability played a prominent role in food selection. Food habits of adult and juvenile ring-necked ducks appear to be more generalized than those of congenerics, but there is considerable overlap in the food taxa consumed by diving ducks (Tribe Aythyini). J. WILDL. MANAGE. 49(3):546-557 Energetic costs of gonadal growth for female ducks and geese are large relative to those of other major groups of birds (King 1973, Ricklefs 1974). Among waterfowl, dependence on breeding ground food resources for reproductive energy and nutrient requirements varies by species and group. Whereas Arctic nesting geese and common eiders (Somateria mollissima) are essentially independent of food resources from arrival on the breeding grounds through incubatio by virtue of reserves accumulated on wintering and staging areas (Korschgen 1977, Ankney and MacInnes 1978, Raveling 1979), most ducks feed intensively on the breeding area. Food needs of breeding waterfowl also vary within species by sex and female body condition (e.g., renesting mallard [Anas platyrhynchos] hens) (Krapu 1981). The diets of 'Present address: Delta Waterfowl Research Station, Rural Route 1, Portage la Prairie, Manitoba R1N 3A1, Canada. This content downloaded from 207.46.13.131 on Sat, 15 Oct 2016 04:19:25 UTC All use subject to http://about.jstor.org/terms J. Wildl. Manage. 49(3):1985 RING-NECKED DUCK FEEDING * Hohman 547 breeding female ducks change seasonally, reflecting changing protein demands. Invertebrates, which are digestible sources of protein with high caloric densities (Reinecke 1977), predominate in female diets during gonadal recrudescence and ovulation (Krapu 1974, Swanson et al. 1974b, Serie and Swanson 1976, Drobney and Fredrickson 1979, Reinecke and Owen 1980, Noyes 1983). Their availability to females may be a major determinant of clutch size (Krapu and Swanson 1975) and laying date (Krapu 1974). Ring-necked ducks are small-bodied (500-900 g), inland diving ducks, which have been studied principally in the Northeast (Mendall 1958). They commonly nest in northern bog-marshes, wetlands of low primary production (Reader 1978, Richardson 1979) that are little used by other ducks. This work was undertaken as part of a study examining energetics of breeding ring-necked ducks. The objectives were to: (1) examine adult ring-necked duck diets in relation to sex and stage of reproduction, and juvenile food habits by age; (2) assess preferences among foods; and (3) estimate rate of food consumption. This paper represents a portion of my Ph.D. thesis work supervised by M. W. Weller and submitted to the Univ. of Minnesota at St. Paul. I was also advised by E. F. Cook, J. A. Cooper, F. McKinney, and J. R. Tester. L. J. Korschgen assisted with seed identifications. R. D. Crawford, R. T. Eberhardt, L. G. Sugden, and M. W. Weller commented on drafts of the manuscript. This is Journal Paper 13838 of the Minn. Agric. Exp. Stn., St. Paul. Financial support was provided by the North Am. Wildl. Found. through the Delta Waterfowl Res. Stn., Minn. Dep. of Nat. Resour., Univ. of Minnesota, Dep. of Fish. and Wildl., Computing Cent., Agric. Exp. Stn., and Graduate School, and the Minn. Waterfowl Assoc.

Comparison of the usefulness of the silver carp and the bighead carp as additional fish in carp ponds

On the basis of fishery results and food analyses of the silver carp, Hypophthalmichthys molitrix, and of the bighead carp, Aristichthys nobilis, it was found that the latter species is less useful for intensive rearing in ponds jointly with the common carp. Although the bighead carp, due to its rapid growth rate, gave a higher level of production than the silver carp at the same stocking densities, the drop in common carp production with bighead was so considerable that there are doubts as to the usefulness of joint rearing of the two species in ponds. Comparisons of the amount and composition of food of the silver carp and the bighead carp lead to the conclusion that food competition of the latter species with respect to the common carp is considerably greater. Although neither silver carp nor bighead carp consumed feed given to the common carp (sorghum), and detritus was the main dietary component of the two former species of fish, the proportion of invertebrates in the food of bighead carp was greater and the components more similar to the food of the common carp. The silver carp consumed smaller zooplankton species, mainly Bosmina longirostris and rotifers, which were of no significance as food for the common carp. The bighead carp consumed large Cladocera and Copepoda species, and also Tendipedidae larvae, i.e. organisms constituting the basic component of the food of common carp.