Main Prey Research Articles

State‐dependent environmental sensitivity of reproductive success and survival in a shorebird

To understand the consequences of anthropogenic and environmental changes for wildlife populations, it is important to study how individuals differ in their sensitivity to environmental change and whether this depends on individual characteristics. An individual's reproductive performance may provide an integrative, unidimensional proxy of an individual's characteristics. In this study, we define an individual's characteristics by three such reproductive states, namely successful, failed and non‐breeders in the previous year. We used a 16‐year dataset of individually marked breeding Eurasian OystercatchersHaematopus ostralegusto examine the interannual fluctuations in reproductive success and survival among breeding states, and their state‐dependent sensitivity to environmental conditions. Environmental conditions included available biomass of the main prey species of breeding Oystercatchers (Ragworm, Baltic Tellin and Lugworm), tidal height, which reflects one of the main causes of nest loss (flooding), and conditions that may impact the energetic requirements during incubation, such as temperature. We also included environmental variables measured in winter, including available biomass of the main winter prey species (Blue Mussel and Common Cockle) along with factors that may affect food availability and energetic requirements for homeostasis, namely bivalve weight loss, windchill, winter severity and precipitation. Breeding birds that were successful the previous year had higher survival and were more likely to remain successful, in comparison with failed or non‐breeders. The effects of environmental conditions acted in the same direction on reproductive success but had opposite effects on survival among the three breeding states, especially for windchill and Blue Mussel biomass. The contrasting state‐dependent effects of the environment on survival thus averaged out when examining consequences for lifetime reproductive nest success (LRnS); instead, LRnS was largely influenced by environmental conditions acting upon reproduction. Our study indicates that an individual's previous breeding state provides an integrative measure of heterogeneity in individuals' sensitivity of reproduction and survival to environmental change. Incorporating previous breeding state as a source of individual heterogeneity in population modelling may improve predictions of future population dynamics in a rapidly changing world.

First evaluation of quantitative fatty acid signature analysis (QFASA) in dolphins

Accurate diet estimation of marine mammals is fundamental to investigate their ecological roles in marine habitats, but it remains a pervasive challenge to researchers due to the constraints associated with conventional methods based on stomach contents or feces analysis, which are imprecise, limited to last meal and often biased. Quantitative fatty acid signature analysis (QFASA), an emerging method for diet estimations, has been demonstrated to be reliable in reconstructing long-term diets of many marine mammal predators; however, its application has not been seriously evaluated in dolphins. To this end, we compared the QFASA estimates obtained using 8 pre-existing calibration coefficient sets, 3 fatty acid subsets, and 3 prey library subsets to the true diet of a captive Indo-Pacific humpback dolphin (Sousa chinensis) that was fed a long-term diet of mostly gizzard shad (Clupanodon thrissa) with smaller proportions of Japanese seabass (Lateolabrax japonicus), pumpkinseed (Lepomis gibbosus), roughscale tonguesole (Cynoglossus lida), and Chinese herring (Ilisha elongate). The diet of the dolphin was best reconstructed using the calibration coefficients derived from captive feeding trials of American mink (Mustela vison) that were fed herring with the “main” fatty acid subset; this process correctly identified gizzard shad as the main prey source of the dolphin with the highest actual diet proportions and lowest predator signature proportions outside the range of the mean prey proportions. In addition, high accuracy and consistency were acquired in the diet estimations obtained using the calibration coefficients derived from minks fed herring and herring plus seal oil even though pseudo-prey were included in our model, revealing the high robustness and reliability of QFASA in reconstructing the dolphin diet. We recommend caution in selecting fatty acid subsets when using fatty acid signatures derived from different studies. Overall, QFASA offers a promising tool to quantify the long-term diets of humpback dolphins and other odontocetes.

The spatial and trophic ecology of culpeo foxes (Lycalopex culpaeus) in the high Andes of northern Chile

ABSTRACT The spatial and trophic ecology of the culpeo fox (Lycalopex culpaeus) was studied in the Salar de Punta Negra basin and the Llullaillaco National Park, in the high Andes of the Region of Antofagasta in northern Chile. The objectives of this study were to understand the feeding ecology, habitat use, and home range and activity pattern of culpeo fox. The study was conducted in an area of approximately 2800 km2 inside the Punta Negra salt flat basin, Llullaillaco NP, the surrounding mountains, and within areas of mining operations. We used methodologies including camera trapping, live trapping and satellite monitoring of L. culpaeus individuals, and diet analysis. Fifteen captures and five recaptures of culpeos were made, and three of them were equipped with satellite tracking collars. The home ranges estimated using the Minimum Convex Polygon (MPC 95%) were: 1029 km2 (female), 809 km2 (female) and 215 km2 (male). Culpeo foxes were nocturnal animals. A larger sample of 282 fecal scats was collected, with the main trophic prey in culpeo fox diet by frequency of occurrence being rodents (74.3%), arthropods (48%), camelids carrion (43.6%), birds (16.3%), vegetation (13.8%) and reptiles (2.5%). Niche breadth was low (0.367).

The predator activity landscape predicts the anti‐predator behavior and distribution of prey in a tundra community

AbstractPredation shapes communities through consumptive and non‐consumptive effects. In the latter case, prey respond to perceived predation risk through proactive or reactive risk management strategies occurring at different spatial and temporal scales. The predator–prey space race and landscape of fear concepts are useful to better understand how predation risk affects prey behavioral decisions and distribution. We assessed predation risk effects in a terrestrial Arctic community, where the arctic fox is the main predator of ground‐nesting birds. Using high‐frequency GPS data, we estimated a predator activity landscape corresponding to fox space use patterns and validated with an artificial prey experiment that this predator activity landscape correlated with the predation risk landscape. We then investigated the effects of the fox activity landscape on multiple prey species, by assessing the anti‐predator behavior of a main prey (snow goose) actively searched for by foxes, and the nest distribution of several incidental prey species. We first found that snow geese showed a stronger level of nest defense in areas highly used by foxes, possibly responding with a reactive strategy to variation in predation risk. Then, nests of incidental prey reproducing in habitats easily accessed by foxes had a lower probability of occurrence in areas highly used by foxes, suggesting these birds may use a proactive risk management strategy by shifting their distribution away from risky areas. For incidental prey species nesting in microhabitat refuges difficult to access by foxes, probability of nest occurrence was independent of predation risk in the surrounding area, as they avoid risk at a finer spatial scale. By tracking all individuals of the dominant predator species in our study area, we demonstrated the value of using predator space use patterns to infer spatial variation in predation risk. Overall, we highlight the diversity of risk management strategies in prey sharing a common predator, hence refining our understanding of the mechanisms driving species distribution and community structure.

Survival rates of adult and juvenile gyrfalcons in Iceland: estimates and drivers.

Knowledge of survival rates and their potential covariation with environmental drivers, for both adults and juveniles, is paramount to forecast the population dynamics of long-lived animals. Long-lived bird and mammal populations are indeed very sensitive to change in survival rates, especially that of adults. Here we report the first survival estimates for the Icelandic gyrfalcon (Falco rusticolus) obtained by capture-mark-recapture methods. We use a mark-recapture-recovery model combining live and dead encounters into a unified analysis, in a Bayesian framework. Annual survival was estimated at 0.83 for adults and 0.40 for juveniles. Positive effects of main prey density on juvenile survival (5% increase in survival from min to max density) were possible though not likely. Weather effects on juvenile survival were even less likely. The variability in observed lifespan suggests that adult birds could suffer from human-induced alteration of survival rates.

Modeling Distribution and Habitat Suitability for the Snow Leopard in Bhutan

The snow leopard (Panthera uncia) is one of the world's most elusive felids. In Bhutan, which is one of the 12 countries where the species still persists, reliable information on its distribution and habitat suitability is lacking, thus impeding effective conservation planning for the species. To fill this knowledge gap, we created a country-wide species distribution model using “presence-only” data from 420 snow leopard occurrences (345 from a sign survey and 77 from a camera-trapping survey) and 12 environmental covariates consisting of biophysical and anthropogenic factors. We analyzed the data in an ensemble model framework which combines the outputs from several species distribution models. To assess the adequacy of Bhutan's network of protected areas and their potential contribution toward the conservation of the species, we overlaid the output of the ensemble model on the spatial layers of protected areas and biological corridors. The ensemble model identified 7,206 km2 of Bhutan as suitable for the snow leopard: 3,647 km2 as highly suitable, 2,681 km2 as moderately suitable, and 878 km2 as marginally suitable. Forty percent of the total suitable habitat consisted of protected areas and a further 8% of biological corridors. These suitable habitats were characterized by a mean livestock density of 1.3 individuals per hectare, and a mean slope of 25°; they closely match the distribution of the snow leopard's main wild prey, the bharal (Pseudois nayaur). Our study shows that Bhutan's northern protected areas are a centre for snow leopard conservation both at the national and regional scale.

Population dynamics of an island population of water voles Arvicola amphibius (Linnaeus, 1758) with one major predator, the eagle owl Bubo bubo (Linnaeus, 1758), in northern Norway

Predator–prey relationships are of great significance to ecosystems, and their effects on the population dynamics of voles and lemmings (Microtinae) in Boreal and Arctic environments have long been of particular interest. A simple ecosystem with one major prey and one major predator could be an ideal setting for a study of their interactions. This is the situation on several small islands on the coast of northern Norway just below the Arctic Circle, with populations of water voles Arvicola amphibius preyed upon by the eagle owl Bubo bubo. The population dynamics of the water vole was studied by trapping and tagging in 2003–2018, eagle owl pellets were collected for analyses, eagle owl breeding attempts were recorded, and some weather variables collected from official recordings. After having been introduced well into the study period, the number of sheep Ovis aries was also recorded. Water voles were the main prey of the eagle owl, with 89% occurrence in pellets, with an overrepresentation of adults and males. Both predation, sheep grazing and extreme weather events influenced the vole population. Predator exclusion, as happened in three summers due to an intensive radio tracking study, especially increased the number of surviving young (in particular from the early cohorts) and the mass of adults. Extreme weather events, such as flooding in summer and deeply frozen ground in winter, most significantly reduced vole populations. Sheep grazing may exacerbate the effects of predation. A similar multitude of factors may affect populations of other rodent species as well.

Seasonal depth distribution and thermal experience of the non-indigenous round goby Neogobius melanostomus in the Baltic Sea: implications to key trophic relations

Native to the Ponto-Caspian region, the benthic round goby (Neogobius melanostomus) has invaded several European inland waterbodies as well as the North American Great Lakes and the Baltic Sea. The species is capable of reaching very high densities in the invaded ecosystems, with not only evidence for significant food-web effects on the native biota and habitats, but also negative implications to coastal fishers. Although generally considered a coastal species, it has been shown that round goby migrate to deeper areas of the Great Lakes and other inland lakes during the cold season. Such seasonal movements may create new spatio-temporal ecosystem consequences in invaded systems. To seek evidence for seasonal depth distribution in coastal marine habitats, we compiled all available catch data for round goby in the Baltic Sea since its invasion and until 2017. We furthermore related the depths at capture for each season with the ambient thermal environment. The round goby spend autumn and winter at significantly deeper and offshore areas compared to spring and summer months; few fish were captured at depths < 25 m in these colder months. Similarly, in spring and summer, round goby were not captured at depths > 25 m. The thermal conditions at which round goby were caught varied significantly between seasons, being on average 18.3 °C during summer, and dropping to a low 3.8 °C during winter months. Overall, the fish sought the depths within each season with the highest possible temperatures. The spatial distribution of the round goby substantially overlaps with that of its main and preferred prey (mussels) and with that of its competitor for food (flatfish), but only moderately with the coastal predatory fish (perch), indicating thereby very complex trophic interactions associated with this invasion. Further investigations should aim at quantifying the food web consequences and coupling effects between different habitats related to seasonal migrations of the round goby, both in terms of the species as a competitor, predator and prey.

Behavioral observations and stable isotopes reveal high individual variation and little seasonal variation in sea otter diets in Southeast Alaska

Two complementary approaches were used to assess year-round variation in the diet of sea otters Enhydra lutris around Prince of Wales Island (POW) in southern Southeast Alaska, a region characterized by mixed-bottom habitat. We observed sea otters foraging to determine diet composition during the spring and summer. Then, we obtained sea otter vibrissae, which record temporal foraging patterns as they grow, from subsistence hunters to identify year-round changes in sea otter diets via stable isotope analysis of carbon (δ13C) and nitrogen (δ15N). We compared the stable isotopes from sea otter vibrissae and sea otter prey items that were collected during spring, summer, and winter. Overall, year-round sea otter diet estimates from stable isotope signatures and visual observations from spring and summer were dominated by clams in terms of biomass, with butter clams Saxidomus gigantea the most common clam species seen during visual observations. Our results indicate that these sea otters, when considered together at a regional level around POW, do not exhibit shifts in the main prey source by season or location. However, sea otter diets identified by stable isotopes had a strong individual-level variation. Behavioral variation among individual sea otters may be a primary driving factor in diet composition. This study provides quantitative diet composition data for modeling predictions of invertebrate population estimates that may aid in the future management of shellfisheries and subsistence hunting and the development of co-management strategies for this protected species.

The diet of Mustelus schmitti in areas with and without commercial bottom trawling (Central Patagonia, Southwestern Atlantic): Is it evidence of trophic interaction with the Patagonian shrimp fishery?

The study compares the diet composition between juveniles and adults of the narrownose smooth-hound Mustelus schmitti in areas with and without commercial bottom trawling using stomach contents. Individuals (n = 291) were caught as by-catch by the bottom-trawl shrimp fishery and by coastal sport anglers in Central Patagonia (Southwestern Atlantic between 43° and 45° S). Results showed that M. schmitti is a mesocarnivorous with a mean trophic level of 3.58. The diet was based mostly on crustaceans (decapods, stomatopods, isopods and amphipods), polychaetes, fishes and cephalopods, in a decreasing order of importance. The diet varied between juveniles and adults, and between individuals captured by the trawling fishery and sport anglers. Crabs were the main prey item observed in the stomach of individuals caught by anglers while the shrimp Pleoticus muelleri was the most consumed prey by individuals caught as by-catch. Juveniles consumed more polychaetes than adults, while the latter consumed mostly shrimp. The presence of shrimp in stomach contents of M. schmitti caught by the commercial fishery is evidence of a trophic interaction between M. schmitti and the fishery. The interaction may be due to the shark and the fleet targeting the same resource, or due to the shark using the discarded shrimp as a food source.

Factors Influencing Dietary Changes of Walleye Pollock, Gadus chalcogrammus, Inhabiting the East Sea off the Korean Coast

This study examined the dietary patterns of walleye pollock, Gadus chalcogrammus, off the middle eastern coast of Korea between January 2016 and December 2017 to determine the influences of various predictors on dietary changes. Based on stomach content analyses, walleye pollock was found to be a demersal carnivore that mainly consumes carid shrimps, euphausiids, mysids, teleosts, and cephalopods. The main prey species identified in the diets of walleye pollock were Euphausia pacifica (euphausiids), Themisto japonicus (amphipods), Neomysis spp. (mysids), Neocrangon communis, Pandalus borealis (carid shrimps), Watasenia scintillans (cephalopods), and Bothrocara hollandi (teleosts), which are hyper-benthic and bentho-pelagic organisms. Dietary analyses based on the weight contributions of different prey taxa to the diets revealed significant variations in dietary composition in terms of fish size, water depth, and season, implying intraspecific dietary segregation. Euphausiids dominate the diets of smaller individuals (&lt;30 cm TL), whereas the contributions of carid shrimps, teleosts, and cephalopods increase as body size increases. Similarly, the latter three prey items are dominant food resources in deeper habitats. The PERMANOVA results revealed that the size-related spatial and temporal changes in dietary composition are all significant for the species, as well as their two- or three-way interactions among those factors, except for the size-depth interaction. The coupling effect of size and depth is indicative of depth-dependent differences in fish sizes, with the tendency for larger individuals to be distributed in deeper habitats. In addition, seasonal and interannual variations in water column structures are also evident in the diets, which may, in part, account for the diet seasonality observed in the stomach content analysis. The dietary analyses of walleye pollock will improve our understandings to seek functional role of the species in benthic food webs, and to predict the effects of environmental and anthropogenic perturbations.

Los restos faunísticos del sitio arqueológico Tembrao (provincia de Río Negro, Argentina)

En este trabajo se presenta el análisis de los materiales faunísticos del sitio Tembrao, ubicado en un pequeño valle al pie de la meseta de Somuncurá (sur de la provincia de Río Negro). Un fechado realizado sobre restos faunísticos ubica la ocupación del lugar en el Holoceno tardío final. El conjunto está conformado principalmente por restos óseos de mamíferos, entre los que predominan los de artiodáctilos. Se propone que los guanacos habrían sido la presa principal de los cazadores recolectores pre-hispánicos, mientras que los restos de ovejas fueron ingresados por las ocupaciones modernas del paraje Tembrao. Se discute la disponibilidad de recursos faunísticos en cercanías del sitio, especialmente de guanacos sobre la meseta de Somuncurá, y las implicancias de la presencia de elementos foráneos (valvas de almejas fluviales y de moluscos marinos, y probablemente cáscaras de huevos de Rhea americana). En base al análisis se infiere un patrón de subsistencia basado en pocas especies, similar al de otras regiones mesetarias de Norpatagonia y claramente diferenciado de aquel del litoral marino y de los valles fluviales.

Plastic debris and natural food in two commercially important fish species from the coast of Peru

The aim of this study was to evaluate the presence of plastic debris in the stomach contents of two commercially important species Ethmidium maculatum and Mugil cephalus from Peru and relate their characteristics to their diet. The contents of 1820 stomachs were analyzed visually to detect the presence of plastics and prey. Of the analyzed samples, 0.3% contained nine microplastic fragments (0.72–4.54 mm) and one mesoplastic fragment (6.65 mm). Green and blue plastics of polyethylene and polypropylene were the most common. In E. maculatum, copepods were the main prey, followed by diatoms and decapods, and they exhibited the highest amount of plastics. In M. cephalus, the main prey were diatoms, copepods, and dinoflagellates, and they exhibited only one type of microplastic. Although the characteristics of the plastics and the prey of these species may be related (sizes–colors), more research is required to understand this problem in commercially important fishery resources in Peru.

A new enemy of Apis mellifera (Hymenoptera: Apidae): First report of Nomamyrmex esenbeckii (Hymenoptera: Formicidae) attacking honey bee colonies

Nomamyrmex esenbeckii, commonly known as the legionary ant, belongs to the group of army ants. This social insect employs a cooperative hunting method that is considered more evolved than solitary hunting ants. Their main preys are other ants and termites. However, in this article, we report for the first time in Mexico the predatory behavior of N. esenbeckii on Apis mellifera colonies.

Winter Diet of an Eurasian Eagle Owl (Bubo bubo) Near the Yedikır Dam, Amasya (Turkey)

Abstract&#x0D; Aim of study: The aim of this study was to contribute to the data on the diet of Eurasian Eagle Owl (Bubo bubo) in Turkey.&#x0D; Area of study: This study was conducted near the Yedikır Dam (Amasya)&#x0D; Material and methods: A total of 12 pellets of the Eurasian Eagle Owl collected in Yedikır Dam was analyzed. The remains of the skull and lower jaw were used for the identification of mammals. &#x0D; Main results: 60 preys were identified to belong to 6 different taxa (5 Rodents and 1 Passerine). The main prey was Mus spp. (35.0%). Only one bird remain was recorded from pellets.&#x0D; Highlights: Pellet analyses were the first step for understanding the diet of B. bubo. Considering, B. bubo is an opportunistic predator and can consume medium-sized mammals and large-sized birds. Hence, a diet study supported with remains that are directly collected from the nest or perching site and their surroundings will reveal more objectively prey preferences for this apex predator.

‘Taking Fishers’ Knowledge to the Lab’: An Interdisciplinary Approach to Understand Fish Trophic Relationships in the Brazilian Amazon

Trophic levels can be applied to describe the ecological role of organisms in food webs and assess changes in ecosystems. Stable isotopes analysis can assist in the understanding of trophic interactions and use of food resources by aquatic organisms. The local ecological knowledge (LEK) of fishers can be an alternative to advance understanding about fish trophic interactions and to construct aquatic food webs, especially in regions lacking research capacity. The objectives of this study are: to calculate the trophic levels of six fish species important to fishing by combining data from stable isotopes analysis and fishers’ LEK in two clear water rivers (Tapajós and Tocantins) in the Brazilian Amazon; to compare the trophic levels of these fish between the two methods (stable isotopes analysis and LEK) and the two rivers; and to develop diagrams representing the trophic webs of the main fish prey and predators based on fisher’s LEK. The fish species studied were Pescada (Plagioscion squamosissimus), Tucunaré (Cichla pinima), Piranha (Serrasalmus rhombeus), Aracu (Leporinus fasciatus), Charuto (Hemiodus unimaculatus), and Jaraqui (Semaprochilodus spp.). A total of 98 interviews and 63 samples for stable isotopes analysis were carried out in both rivers. The average fish trophic levels did not differ between the stable isotopes analysis and the LEK in the Tapajós, nor in the Tocantins Rivers. The overall trophic level of the studied fish species obtained through the LEK did not differ from data obtained through the stable isotopes analysis in both rivers, except for the Aracu in the Tapajós River. The main food items consumed by the fish according to fishers’ LEK did agree with fish diets as described in the biological literature. Fishers provided useful information on fish predators and feeding habits of endangered species, such as river dolphin and river otter. Collaboration with fishers through LEK studies can be a viable approach to produce reliable data on fish trophic ecology to improve fisheries management and species conservation in tropical freshwater environments and other regions with data limitations.

FEEDING HABITS OF THE STYGIAN OWL (ASIO STYGIUS) AND THE SHORT-EARED OWL (A. FLAMMEUS) IN THE SOUTHWEST OF BOGOTÁ SAVANNA, CUNDINAMARCA, COLOMBIA

This study quantitively compares the diets of the Stygian Owl (Asio stygius) and the Short-eared Owl (A. flammeus) in the south-west of the Bogotá Savanna, Colombia. We identified 130 prey items from 111 A. stygius pellets and 579 prey items from 149 A. flammeus pellets. In terms of the numbers of preys, the diet of A. stygius consisted of the following: 88.1% birds, mainly pigeons, rails and cuckoos; and a smaller proportion of beetles (11.4%). In the diet of A. flammeus, insects were the most frequent prey item (59.8%), followed by rodents (39.8%), and birds (0.5%). In terms of biomass contribution, the main preys in the diet of A. stygius were Eared Doves (Zenaida auriculata) (54%) and Purple Gallinules (Porphyrio martinica) (19.3%), while the diet of A. flammeus consisted mainly of House Mice (Mus musculus) (65.2%). Diet diversity varied between the owl species: A. flammeus was more selective in its hunting habits, while A. stygius was more of an opportunistic predator. It is important to quantify the ecosystem services these owls provide not only by controlling M. musculus, Z. auriculata, and Shiny Cowbird (Molothrus bonariensis) populations, which can affect human well-being and threatened species populations, but also through secondary seed dispersion and birdwatching opportunities.

Ontogenetic diet shifts of rough scad Trachurus lathami in the North Patagonian shelf (south-west Atlantic Ocean).

Rough scad Trachurus lathami is a key pelagic fish in the Argentinean continental shelf (ACS, south-west Atlantic Ocean), with recent increases in abundance. It is a main prey of fishes and marine mammals, and shares the environment with commercially relevant pelagic species (Engraulis anchoita and Scomber colias), playing an important role linking lower and upper trophic levels in the ecosystem. This study aims to determine the ontogenetic changes in the diet composition, feeding strategy, trophic niche breadth and trophic level of T. lathami in the North Patagonian Shelf (43°-45°30'S). The stomach contents of adult fish (n=238) were analysed. The results suggest a clear ontogenetic shift in the diet at a size of ~190 mm. Smaller individuals (160-190 mm) were specialized on misidaceans, and showed the highest trophic level, while larger T. lathami (221-230 mm) consumed decapods (Peisos petrunkevitchi) and teleosts (eggs and larvae). Trophic niche breadth was higher at the medium-sized class (191-220 mm), which mainly preyed on copepods (Calanoides carinatus) and chaetognaths (Sagitta spp.), evidencing a more diverse diet and a rather generalist strategy. Updated information on the trophic ecology of T. lathami evidences its extremely plastic feeding behaviour, being able to adapt its trophic niche to the most readily available food items from the mesopelagic community.

First report the role of benthic macroinvertebrates as preys for native fish in Toltén river (38° S, Araucania region Chile)

The Toltén river is located in the 137 years old Araucania region, Chile (38° S), and is characterized by low alterations through human interference due agriculture and towns in its surrounding basin, the presence of native fishes and salmonids, and by its lake effluent regime originated from Villarrica lake. The aim of the present study was to make a review of ecological role of the benthic inland water macroinvertebrates as preys for native fishes of the River Toltén, in order to understand their importance in the ecosystem of the river. The literature revealed that the main prey for native fishes are Chironomidae larvae, nevertheless there are not specific reports for Tolten river. The exposed results are similar with similar native species for Patagonia, and these native species would have prey for introduced salmonids, or these species would have prey competition with introduced salmonids in according to the literature descriptions for Argentinean and Chilean Patagonia.

Identification of Little Tern (Sternula albifrons) Prey in Inland Andong Lake, Korea Using Video Image Analysis

Little Tern (Sternula albifrons) prey composition was studied on a sandy islet in inland Andong Lake, Republic of Korea, during the breeding season (April to July 2018). Two remote-control video cameras with 4K-resolution were set on the islet to identify prey and determine whether prey species composition or size differed among breeding stages. On still images in which terns had prey in their bills (n = 1,275), prey species were identified, classified to five length-categories, and compared among breeding stages. Freshwater fishes dominated the observed diet (100%; 11 species overall), where the landlocked pond smelt (Hypomesus nipponensis; 80.8%) and largemouth bass (Micropterus salmoides; 13.7%) were main prey species. The mean prey length was 51.0 ± 20.89 mm, where 50.1–75.0 mm prey was the most frequent in the diet (42.2%) and varied significantly among breeding stages; 50.1–75.0 mm prey were most frequent during courtship and incubation stages, whereas 1.0–25.0 mm prey were most frequent at the chick-rearing stage. Surface water temperatures exceeded the upper thermal tolerance of the primary prey species at a date coincidental with tern departure from the colony.