Piscivorous Birds Research Articles

Massive hepatic trematodosis in 5 juvenile bald eagles.

Hepatic trematodosis by opisthorchiid flukes has been reported sporadically in North American fish-eating raptors. Bald eagles (Haliaeetus leucocephalus) infected by these flukes often have various degrees of granulomatous cholangitis, pericholangitis, necrosis of adjacent hepatocytes, and subsequent hepatic fibrosis. Species identification has been complicated by the inability to dissect intact specimens from liver tissue. Between 2007 and 2018, 5 juvenile bald eagles with massive hepatic trematodosis were identified at autopsy. Histologically, flukes were non-spinous. Parasitologic identification revealed ventral suckers (80-93 µm diameter), and uteri containing golden, operculated eggs (~25.0 × 12.0 µm). An unfixed frozen liver sample of one eagle was analyzed by PCR and DNA sequencing targeting the large subunit rRNA, ITS region, and cox1 genes of the parasite. The fluke DNA sequences shared 99.6%, 98.4%, and 87.0% similarity, respectively, with Erschoviorchis anuiensis, a newly described opisthorchiid species infecting the liver and pancreas of fish-eating birds in Europe and Asia. Infection by E. anuiensis is highly pathogenic in several piscivorous bird species. The clinical significance of trematodosis in our 5 cases is uncertain because all birds had comorbidities.

Seasonal fluctuations attenuate stimulatory or inhibitory impacts of colonial birds on abundance, structure and diversity of soil biota.

Soil microorganisms and free-living nematodes were investigated in association with the nesting and roosting habitats of the following piscivorous and omnivorous colonial birds: black kite (Milvus migrans), great cormorant (Phalacrocorax carbo), black-crowned night heron (Nycticorax nycticorax) and little egret (Egretta garzetta), in Israel's Mediterranean region. Abiotic variables, abundance, trophic structure, sex ratio and genus diversity of soil free-living nematodes, and total abundance of bacteria and fungi, were measured during the wet season, following our previous study conducted during the dry season. The observed soil properties were important drivers of soil biota structure. Presence of the most efficient elements for soil organisms, such as phosphorus and nitrogen, was strongly dependent on the diet of the compared piscivorous and omnivorous bird colonies; levels of these nutrients were notably higher in the bird habitats than in their respective control sites during the study period. Ecological indices showed that the different species of colonial birds can have different (stimulatory or inhibitory) impacts on abundance and diversity of the soil biota, affecting the structure of the soil free-living nematode population at the generic, trophic and sexual levels during the wet season. A comparison with results from the dry season illustrated that seasonal fluctuations can change, and even attenuate the effect of bird activity on the abundance, structure and diversity of the soil communities.

Mercury distribution inthe great cormorant (Phalacrocorax carbo) from the Krogulna ponds and Nysa Kłodzka River (Poland).

Mercury belongs among the highly hazardous substances present inthe environment and represents agreat health risk for many animals including predatory and piscivorous birds. The aim ofthis study was toassess the total mercury content inthe main detoxifying organs (liver and kidney) and inthe muscles ofadult great cormorants (Phalacrocorax carbo) caught attwo localities (the Krogulna ponds and the Nysa Kłodzka River) insouthern Poland. The aim was tocompare the locality with the iron ore mining history (the Krogulna ponds) with asite without such load (the Nysa Kłodzka River). The total mercury content inthe great cormorants decreases asfollows: kidneys> liver> muscle inboth monitored localities and significantly differs between the localities. Theaverage mercury content varied from 0.58±0.38mg/kg (muscle) to1.39±1.42mg/kg (kidney) inthe cormorantfrom the Krogulna ponds and from 1.09±0.40mg/kg (muscle) to3.12±1.55mg/kg (kidney) inthe cormorant from the Nysa Kłodzka River. The accumulation ofmercury does not correlate with the mining history asit was higher atthe Nysa Kłodzka River, but itis probably influenced bythe different fish stocks inthese two localities (omnivorous fish inthe Krogulna ponds versus predatory fish inthe Nysa Kłodzka River).

Assessment of the correlation between the nutrient load from migratory bird excrement and water quality by principal component analysis in a freshwater habitat

Waterbirds depend on a dispersed network of wetlands for their annual life cycle during migration. Climate and land use changes raise new concerns about the sustainability of these habitat networks, as water scarcity triggers ecological and socioeconomic impacts threatening wetland availability and quality. During the migration period, birds can be present in large enough numbers to influence water quality themselves linking them and water management in efforts to conserve habitats for endangered populations. Despite this, the guidelines within laws do not properly account for the annual change of water quality due to natural factors such as the migration periods of birds. Principal component analysis and principal component regression was used to analyze the correlations between the presence of a multitude of migratory waterbird communities and water quality metrics based on a dataset collected over four years in the Dumbrăvița section of the Homoród stream in Transylvania. The results reveal a correlation between the presence and numbers of various bird species and the seasonal changes in water quality. Piscivorous birds tended to increase the phosphorus load, herbivorous waterbirds the nitrogen load, while benthivorous duck species influenced a variety of parameters. The established PCR water quality prediction model showed accurate prediction capabilities for the water quality index of the observed region. For the tested data set, the method provided an R2 value of 0.81 and a mean squared prediction error of 0.17.

Endurance Swimming Is Related to Summer Lake Survival of Rainbow Trout in a Warm Lake with Avian Piscivores

Fitness of fish is assumed to be influenced by locomotion performance, but empirical evidence linking swimming capacity to survival in nature remains sparse. Poor triploid (3N) fish aerobic swimming performance in conjunction with production of sibling diploid (2N) and 3N populations of genetically identical origin to minimize variability among compared populations make 3N trout an informative system to test hypotheses about fitness consequences of fish locomotion. Here, we ask if reduced survival of 3N relative to 2N trout in natural ecosystems during periods of high temperature relate to a lower aerobic swimming capacity and aerobic scope of 3N compared with 2N conspecifics. Three-yearly cohorts of conspecific 2N and 3N hatchery-reared, yearling rainbow trout were ranked for swimming endurance, externally marked for their endurance quantile, and then stocked into two lakes as yearlings to quantify their survival in the wild over summer as a function of ploidy, temperature and endurance; all while tracking temperature and depth habitat utilization via telemetry. As expected, 3N swimming endurance was lower than that of 2N, but with considerable individual overlap. Aerobic swimming endurance, especially for 3N, was predictive of summer survival in a warm lake where piscivorous birds potentially exerted high predation pressure, resulting in low fish survival. This empirical evidence of a connection between swimming endurance and fitness provides support for long held assumptions of this relationship and could inform future sport fishing stocking industry practices to match fish strains to ideal habitats.

Evaluation of a snail trap prototype for monitoring the intermediate gastropod hosts of Bolbophorus spp. in commercial catfish ponds of the southeastern United States

AbstractBolbophorus damnificus is a digenetic trematode causing significant economic losses within the United States commercial catfish industry. The indirect life cycle is complex, requiring piscivorous birds, aquatic snails, and fish to complete. With federal protections on many piscivorous birds and no FDA‐approved therapeutic treatment for trematode infections in fish, management within the catfish industry is primarily limited to controlling the snail host. Planorbella trivolvis and Biomphalaria havanensis are snails commonly found in commercial catfish ponds and known to transmit B. damnificus. This study evaluated a low‐cost snail trap prototype for monitoring populations of these snails in efforts to better inform treatment regimes. Snail traps were deployed into ponds on a commercial catfish farm and checked weekly throughout the production season. All snails were identified and counted to evaluate trap efficacy. Traps captured significantly more snails in foodfish ponds than in fingerling ponds; however, this trend was not present in monthly box samples. B. havanensis was rarely collected and was only found consistently within one pond, while P. trivolvis was routinely collected from all ponds, although abundance varied widely among ponds. Snail traps could be a useful, low‐cost method to monitor snail populations within ponds and better inform control treatments.

Long term changes in aquaculture influence migration, regional abundance, and distribution of an avian species.

Agricultural development has been causing changes to the environment and the abundance and distribution of avian species. Agriculture is dynamic with changes in products occurring at large scales over relatively short time periods. The catfish aquaculture industry is one such agriculture industry that has undergone dramatic changes over the last 25 years. The double-crested cormorant (Nannopterum auritum) is a piscivorous bird that has an extensive history with the aquaculture industry of Mississippi due to its depredation of cultured catfish. A large-scale monitoring program began in 1989 to estimate the abundance and location of cormorants at every known roost in the primary catfish producing region of the state, regionally known as the Delta. We used this data set to address hypotheses pertaining to cormorant ecology within the Delta over time, particularly in relation to aquaculture. We found that, although the Midwest breeding population of cormorants has been increasing, the abundance of cormorants wintering in the Delta has been decreasing, closely following the decline of aquaculture, suggesting aquaculture area is the primary reason for cormorant inhabitation of the region. We also modeled cormorant presence and abundance at all roost sites to determine what factors most influenced cormorant distribution. Aquaculture area around roosts was a significant predictor of both cormorant presence and abundance. However, the influence of aquaculture area was seasonally dependent, with greater positive influences occurring prior to migration. Lastly, we found peak cormorant abundance in the Delta is occurring 2.14 days earlier each year, which may be indicative of changes to migration phenology. Information gained using this large dataset aids in cormorant damage mitigation and to further our understanding of cormorant ecology. Data indicate changes in agriculture, and potentially climate change, can influence phenology, distribution, and abundance of avian species at large geographic scales.

The genus Contracaecum Raillet & Henry (Nematoda: Anisakidae): host and geographical distribution on Neotropical and Antarctic species

Nematodes of the genus Contracaecum Raillet & Henry, 1912 (Anisakidae, Contracaecinae) have a worldwide distribution. The taxonomy of the genus Contracaecum is well-known nowadays due to several morphometric studies, scanning electron microscopy, and molecular biology. The aim of this work was to review, clarify, and summarize the valid species of the genus Contracaecum parasitizing piscivorous sea birds and mammals from both the Neotropical and Antarctic regions reviewing all scientific available papers and electronic searching data up to date. A checklist on Neotropical and Antarctic Contracaecum spp. was organized through a revision of scientific papers and original descriptions. The systematic online search and the most updated papers were obtained through SCOPUS, Google Scholar, PubMed, Medline, World Register of Marine Species, etc. We provide information about hosts, Neotropical and Antarctic localities where worms were collected, references, molecular markers, and Genbank accession numbers. Twenty-five Neotropical and Antarctic Contracaecum species have been recorded up to date and checked out as valid ones according to the most updated data. Twenty-one species parasitize exclusively fish-eating birds, two species were reported only on marine mammals, and the other two parasitize both sea birds and mammals. A total of 20 Contracaecum species are exclusively reported for the Neotropical region, three only for Antarctic hosts, and two species were reported parasitizing both Neotropical and Antarctic hosts. Several Contracaecum species (10) have been corroborated by molecular analysis of different genetic markers. After reviewing all morphological descriptions of the Contracaecum species, and despite most of them have been characterized only by morphometric methods, we are convinced that all species listed in this work correspond to good and valid Contracaecum Neotropical and Antarctic species. Present results indicate that more taxonomic and molecular studies are needed to advance the understanding of the distribution and host specificity of the Contracaecum species.

Multispecies collective waving behaviour in fish.

Collective behaviour is widely accepted to provide a variety of antipredator benefits. Acting collectively requires not only strong coordination among group members, but also the integration of among-individual phenotypic variation. Therefore, groups composed of more than one species offer a unique opportunity to look into the evolution of both mechanistic and functional aspects of collective behaviour. Here, we present data on mixed-species fish shoals that perform collective dives. These repeated dives produce water waves capable of delaying and/or reducing the success of piscivorous bird attacks. The large majority of the fish in these shoals consist of the sulphur molly, Poecilia sulphuraria, but we regularly also found a second species, the widemouth gambusia, Gambusia eurystoma, making these shoals mixed-species aggregations. In a set of laboratory experiments, we found that gambusia were much less inclined to dive after an attack as compared with mollies, which almost always dive, though mollies dived less deep when paired with gambusia that did not dive. By contrast, the behaviour of gambusia was not influenced by the presence of diving mollies. The dampening effect of less responsive gambusia on molly diving behaviour can have strong evolutionary consequences on the overall collective waving behaviour as we expect shoals with a high proportion of unresponsive gambusia to be less effective at producing repeated waves. This article is part of a discussion meeting issue 'Collective behaviour through time'.

Great cormorant (Phalacrocorax carbo sinensis) predation on adult anadromous brown trout (Salmo trutta)

AbstractThe increase in abundance of great cormorants (Phalacrocorax carbo sinensis) over the last decades has caused concern for the sustainability of fish populations. Cormorants are opportunistic piscivorous birds that eat fish from a wide range of species and sizes, in marine, lacustrine and riverine habitats. It has been documented that juvenile salmonids are under significant predation pressure by great cormorants, although knowledge on the predation of adult salmonids by cormorants is limited. In this study, adult anadromous brown trout (Salmo trutta) were tagged over multiple years with PIT tags during their spawning migration in a Danish lowland river. Two nearby cormorant colonies were subsequently scanned for PIT tags to estimate predation rate. It was estimated that by minimum 15.4% of tagged adult sea trout were predated by cormorants. The majority of the individuals were predated in the river, and females were more likely to be predated than males. Moreover, length had a significant effect on predation probability: individuals between 35 and 43 cm had the highest likelihood to be predated, while smaller and larger individuals were less likely to be predated. Our findings challenge the assumption that cormorants do not prey on reproductively mature salmonids. Furthermore, predation of mature individuals may have implications for the recruitment and sustainability of the population.

Molecular and morphological characterization of Andracantha gravida (Alegret, 1941) (Acanthocephala: Polymorphidae) in piscivorous birds from the Gulf of Mexico.

Adult specimens of Andracantha gravida (Alegret, 1941) were recorded from the intestines of the double-crested cormorant Nannopterum auritus (Lesson) (type host) and brown pelican Pelecanus occidentalis L. in two localities from Mexico: Celestún, Yucatan (south-eastern) and Punta Piedra, Tamaulipas (north-eastern). The specimens of A. gravida are morphologically characterized by having a pipe-shaped body without swellings, the absence of small trunk spines between the two fields of spines on the foretrunk and a cylindrical proboscis with 14-16 rows of 10-12 hooks per row. Newly generated partial sequences of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene were generated from adult isolates of A. gravida from Mexico and compared with one sequence of A. gravida and with sequences of other polymorphid acanthocephalans available in GenBank. Phylogenetic analyses based on maximum likelihood and Bayesian inference methods of the cox1 dataset placed all the species of Andracantha in a single clade, with weak support. The analyses of the cox1 dataset placed Andracantha sigma Presswell, García-Varela & Smales, , as sister to the clade formed by A. gravida, Andracantha phalacrocoracis (Yamaguti, 1939), Andracantha leucocarboi Presswell, García-Varela & Smales, and an unidentified species of Andracantha from Japan. The newly generated cox1 sequences of A. gravida from piscivorous birds of Mexico formed a strongly supported clade with the published sequence of A. gravida from the double-crested cormorant from the south-eastern coast of Mexico. The intraspecific genetic divergence among isolates identified as A. gravida ranged from 0.0% to 2.2%. A cox1 haplotype network inferred with 14 sequences revealed the presence of nine haplotypes, two of which were shared between the populations of piscivorous birds from the north-eastern and south-eastern coasts of Mexico and seven of which were unique. The fixation index between the populations from north-eastern and south-eastern Mexico was low (0.06949), which suggests genetic flow. This can be explained by the migration patterns of the brown pelican and the double-crested cormorant along the coasts of the Gulf of Mexico.

Features of the vertebral column and caudal fin skeleton for identifying Engraulis australis in food of the Australasian gannet Morus serrator, Hauraki Gulf, New Zealand.

Identifying fish species from their bone remains is employed in identifying the prey of aquatic animals. However, diagnostic skeletal descriptions are scarce for fish species prey found in the food of piscivorous birds and other marine predators in New Zealand. The present article addresses this knowledge gap, providing a diagnostic description for the vertebral column and the skeleton of the caudal fin of the Australian anchovy Engraulis australis inhabiting coastal waters in and around the Hauraki Gulf, New Zealand. The vertebral column of E. australis is divided into four morphologically distinct regions more complicated than the classical division in abdominal and caudal parts only and the drawing of characteristic-looking vertebral profiles. Each of these four regions is associated with characteristic vertebral profiles. These morphological descriptive parameters express a morphotype that may be linked with the swimming mode of the Australian anchovy. The skeleton of the caudal fin of E. australis showed distinctive characteristics that will be useful as diagnostic criteria to identify specimens of the Australian anchovy and separate them from the skeletal elements of other fish species found in the food of gannets and other marine predators in future studies.

Effectiveness of physical barriers and enhanced fertilization in controlling predation on tilapia and catfish aquaculture systems by four piscivorous water bird families

Waterbirds cause substantial fish-stock losses in open aquaculture systems, particularly in developing countries where fish-ponds are smaller and predator control methods largely manual or under-resourced. This study: (1) used three fish-pond treatment meassures to assess their efficiencies in deterring predation pressure by four piscivorous waterbird families in small tilapia and catfish farms in western Kenya; and (2) distinguished bird group(s) most effectively deterred by these measures. The treatment measures were: coarse-grid wire mesh barriers; finer-grid wire barriers; and enhanced pond fertilization. Twelve fish-ponds were randomly sampled to assess birds' pond-neigborhood assemblages and their predation deterrence responses to pond treatment effects. Bird species richness was not affected by pond cover status, enhanced pond fertilization or type of pond cover barrier. However, pond-cover status, singularly and interactively with enhanced fertilization, reduced bird encounter rates while cover barrier type did not. Conversely, cover status, cover barrier type and fertilization each separately but not interactively contributed to improved deterrence to bird predation rates overall. However, while predation by families of larger birds was effectively reduced by enhancing pond fertilization or cover barriers, predation by families of smaller birds was prevented only by fine-grid chicken-mesh barriers. These results demonstrate that using enhanced fertilization and physical barriers can significantly contribute to reduction in predation pressure on open-culture pond-fish by most piscivorous birds, but may not always be effective if used separately. Effectiveness of combination of measures chosen will depend on types of target bird species and their feeding habits. The results constitute additional knowledge on field techniques useful in diversifying solution options for minimizing impacts of vertebrate predation on pond-fish stocks toward promoting sustainable aquaculture production and improving rural human nutrition.

Characterization of Clinostomum (Digenea: Clinostomidae) spp. in India

Platyhelminths belonging to the family Clinostomidae (Digenea) have a worldwide distribution and are known to infect piscivorous birds through their intermediate hosts, usually fish species. In the present study, clinostome metacercariae were collected from fish hosts, including Channa punctata (Bloch 1793) (n = 25) and Trichogaster fasciata Bloch and Schneider 1801 (n = 25), from a freshwater system in India. The experimental infection of cattle egrets, Ardea (Bubulcus) ibis Linnaeus 1758, with some of the live metacercariae found in the present study was successful. Live adult parasites were obtained from the buccal cavity of the birds. Both metacercaria and adult specimens were subjected to molecular studies to obtain the sequences of 28S, ITS1, and ITS2 (nuclear rDNA) regions. The parasites were found to belong to three species, Clinostomum giganticum Agarwal 1959; C. piscidium Southwell and Prashad 1918; and Euclinostomum heterostomum (Rudolphi 1809). Phylogenetic analyses of the sequences obtained from the adults and metacercariae established a link between the metacercariae in the fish hosts and adults in the avian host, which is essential to elucidate their partial life cycle and specify morphological characteristics in the metacercarial stage.

Cryptokotyle lühe, 1899 (trematoda: heterophyidae): special characteristics of developmental biology and epizootiology

This review presents the scientific studies data on the special characteristics of developmental biology and epizo- otiology of Cryptocotyle trematodes, which belong to Heterophyidae family and pose a threat to the health of the endotherms, including humans, i.e., it is a typical zoonosis. These trematodes are predominantly widespread in the Mediterranean region, namely, in the western Mediterranean region and the Aegean province. The trematodes of Cryptocotyle genus are found in Europe, Asia, North and South America, and Antarctica. They are typical bio- helminths, i.e., they have a complicated life cycle, where the initial intermediate hosts are mollusks, the second ones – fish of different species, the definitive and final hosts are piscivorous birds, carnivorous animals (foxes, wolves, dogs, cats, etc.), and humans. Cryptocotylosis is remarkable for its seasonal prevalence, which depends on the climatic zoning of territories. For instance, in the territorial waters of Ukraine, the highest indices of crypto- cotylosis invasion among Agonidae fish are mainly observed in summer and autumn, but the peak of the invasion comes in autumn. The parasitizing of Cryptocotyle trematodes in the organism of mollusks impacts the reproduc- tion ability and behavioral specificities (motility) of the latter. The invaded fish have black pigment spots on the surface of their bodies – these are metacercariae. In the organism of definitive hosts, the agent is localized in the gastrointestinal tract and may cause inflammatory processes in the mucous membrane of the intestines and changes in parenchymatous organs, which demonstrates the toxic effect of the parasite on the host organism. The diagnos- tics of cryptocotylosis is based on detecting the agent in the host organism and its further taxonomic identification by its anatomic and morphological specificities. The pollution of the aqueous medium with organic and inorganic residues impacts the organisms of both hosts and parasites.

Cost of regulations on US catfish farms

AbstractUnderstanding the economic effects of regulations on US aquaculture farms provides insights into which compliance costs create the greatest compliance burden on farms. This can further guide strategies to improve the efficiency of regulatory frameworks and potentially reduce on‐farm compliance costs while maintaining adequate oversight. This study estimated the regulatory compliance burden on US catfish farms as part of a national effort to quantify the cost of regulations on US aquaculture farms. Completed survey interviews of catfish farms in the major catfish‐producing states covered 63% of the total US catfish production area. Total regulatory costs of the US catfish industry were estimated at $45 million annually. Lost farm revenues (measured as the value of lost production, the value of markets lost from regulations, and the value of business opportunities lost because of regulations) were estimated to be $35 million per annum. Catfish‐producing states outside the Alabama/Arkansas/Mississippi region had the highest ($2856/ha) and Alabama the lowest ($1127/ha) regulatory costs per hectare among the surveyed states. The greatest regulatory cost burden on catfish farms ($18 million) was caused by environmental regulations related mostly to the management of federally protected piscivorous migratory birds, followed by labor regulations ($12 million), and taxes/insurance ($7 million). Regulatory costs ($/kg) were 2.6 times higher on smaller (<80 ha) farms relative to larger (>300 ha) farms. Attention is needed to identify alternative regulatory frameworks that provide the same degree of regulatory oversight but are more cost‐efficient.

Significant impact of allochthonous nutrient loads on microarthropods in forest soils

Aim of study: To investigate the impact of allochthonous material from piscivorous birds on forest soil microarthropod communities.
 Area of study: Six study zones in the Curonian Spit peninsula (western Lithuania) were designated in Pinus sylvestris stands with nesting sites of the great cormorants, taking into account the relief and the duration of the ornithogenic impact.
 Materials and methods: The total abundance of mites and Collembola and the species richness and diversity of Oribatida and Gamasina mites were assessed and compared.
 Main results: The abundance of Collembola, Tarsonemidae and Acaridae mites positively correlated with ornithogenic activity, while Oribatida and Gamasina mites decreased significantly. The structure of microarthropod communities was similar in most of the studied zones, except for the active nesting zone and the abandoned part of the colony on the dune slope. The greatest species richness of Oribatida and Gamasina was found in the unaffected forest in the dune hollow, whereas the lowest value was found in the active nesting area and in the abandoned part of the colony on the dune slope. Of the environmental parameters studied, soil pH (r = - 0.725) and tree layer (r = 0.827) were those most significantly related to the changes of microarthropod communities.
 Research highlights: We found that cormorant colonies have a strong impact on forest ecosystems and soil properties, leading to significant changes in soil microarthropod communities. Birds thus create a natural disturbance experiment that can help reveal the factors that determine the diversity and composition of natural microarthropod communities.

Factors influencing lead, mercury and other trace element exposure in birds from metal mining areas

Non-ferrous metal mining is considered one of the largest sources of toxic metal released to the environment and may threaten ecosystems, notably biota. We explored how birds that inhabit non-ferrous metal mining sites are exposed to mercury, lead, and other trace elements by analyzing their feathers and verifying which factors may influence element concentrations in feathers. We sampled a total of 168 birds, representing 26 species, with different feeding habits and migration patterns in a non-polluted reference site and two historical metal mining areas: Almadén, which is considered one of the most heavily mercury-contaminated sites worldwide, and the Sierra Madrona mountains where lead has been mined since ancient times. The quantification of aluminum (Al), arsenic (As), barium (Ba), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), selenium (Se), thorium (Th), thallium (Tl), uranium (U), vanadium (V) and zinc (Zn) was performed by inductively coupled plasma mass spectrometry (ICP-MS). Feather analysis revealed contamination by Hg and Pb, in Almadén and Sierra Madrona, respectively. We found that granivorous birds had the lowest feather Hg levels compared to those found in omnivorous, insectivorous, and piscivorous species, whereas feather Pb was about twice as high in granivores and omnivores, than in insectivorous and piscivorous birds. We also found differences among study sites in 13 elements and confirmed the influence of feather age, migratory patterns of the birds, and external deposition of elements, on metal concentrations in the feathers. Our results highlight that despite the cessation of metal mining in the study areas, local avifauna are being exposed to Hg and Pb from abandoned mines and old tailings sites, indicating that appropriate measures are needed to protect biota from overexposure to these toxic metals.

Microchemical provenancing of prey remains in cormorant pellets reveals the use of diverse foraging grounds.

Piscivorous birds in aquatic ecosystems exert predation pressure on fish populations. But the site‐specific impact on fish populations, including stocked and commercially used fish species, remains disputed. One of the key questions for the management of piscivorous birds and fish is determining the origin of prey and thus which fish populations are targeted by the birds. We addressed this question by provenancing otoliths (earstones) of fish obtained from regurgitated pellets of piscivorous birds by otolith microchemistry analysis. We retrieved otoliths from regurgitated pellets of great cormorants (Phalacrocorax carbo sinensis) collected every 2 weeks for 2 years from breeding and roosting colonies at Chiemsee in Bavaria, Germany, and classified them according to family or species. We collected water samples from Chiemsee and potential surrounding foraging grounds. We measured the strontium (Sr) 87Sr/86Sr isotope ratio and Sr mass fraction of water and otoliths using (laser ablation) inductively coupled plasma‐mass spectrometry. We assigned otoliths from regurgitated pellets to habitat clusters of origin by comparing the Sr isotopic and elemental composition of otoliths and waterbodies. In 36% of cormorant pellets collected at Chiemsee, prey was assigned to waterbodies distinct from Chiemsee. Furthermore, cormorants used different foraging sites during 1 day. Microchemical provenancing of prey remains can contribute to identifying foraging sites of piscivorous birds and to what extend the birds switched among foraging sites.

The dominant species of piscivorous bird does not adversely affect fishery in the lagoons of the southern Baltic Sea

The impact of fish-eating birds on fishery has long been debated. It is therefore important that the arguments in this debate be scientifically based. The Great Cormorant Phalacrocorax carbo is a flagship example of a conflict species that has been well studied. In some areas, however, such as the southern Baltic estuarine lagoons, the Goosander Mergus merganser may be more abundant, exerting a potentially greater impact on fisheries. However, this aspect has not been well studied in this region, so this article is an attempt to fill this knowledge gap. Based on the digestive tract content of 23 Goosander drowned in gillnets in Poland, it was found that the most frequently consumed species was Ruffe Gymnocephalus cernua (70% of biomass), followed by Zander Sander lucioperca (13% of biomass), Perch Perca fluviatilis (9% of biomass) and Roach Rutilus rutilus (8% of biomass). Average Goosander numbers in the Vistula and Odra estuaries in 2011–2018 were 11,000 in winter, 4,500 in spring and 2,800 in autumn. These fish-eating ducks were found to consume 242 t of fish annually during this period, whereas at the same time fishermen caught an average of 4,400 t of fish. The species caught by both Goosander and fishermen were mainly Zander (32 t vs 189 t), Perch (21 t vs 668 t) and Roach (19 t vs 701 t). No negative impact of Goosander foraging in the winter preceding the fishery season was demonstrated for any of the above species (Zander R2 = 0.022; Perch R2 = 0.834; Roach R2 = 0.881).