Prey Taxa Research Articles

Molecular gut content analysis indicates the inter- and intra-guild predation patterns of spiders in conventionally managed vegetable fields.

Inter‐ and intra‐guild interactions are important in the coexistence of predators and their prey, especially in highly disturbed vegetable cropping systems with sporadic food resources. Assessing the dietary range of a predator taxon characterized by diverse foraging behavior using conventional approaches, such as visual observation and conventional molecular approaches for prey detection, has serious logistical problems. In this study, we assessed the prey compositions and compare the dietary spectrum of a functionally diverge group of predators—spiders—to characterize their trophic interactions and assess biological control potential in Brassica vegetable fields. We used high‐throughput sequencing (HTS) and biotic interaction networks to precisely annotate the predation spectrum and highlight the predator–predator and predator–prey interactions. The prey taxa in the gut of all spider families were mainly enriched with insects (including dipterans, coleopterans, orthopterans, hemipterans, and lepidopterans) with lower proportions of arachnids (such as Araneae) along with a wide range of other prey factions. Despite the generalist foraging behavior of spiders, the community structure analysis and interaction networks highlighted the overrepresentation of particular prey taxa in the gut of each spider family, as well as showing the extent of interfamily predation by spiders. Identifying the diverse trophic niche proportions underpins the importance of spiders as predators of pests in highly disturbed agroecosystems. More specifically, combining HTS with advanced ecological community analysis reveals the preferences and biological control potential of particular spider taxa (such as Salticidae against lepidopterans and Pisauridae against dipterans), and so provides a valuable evidence base for targeted conservation biological control efforts in complex trophic networks.

Nestling diet of the Algerian Nuthatch Sitta ledanti, an endemic threatened bird in Babors’ Kabylia region (north-eastern Algeria)

The Algerian Nuthatch is an endemic and protected bird species in Algeria, and its different habitats are threatened by fires and others human actions; the species is therefore considered ‘Endangered’. A faecal samples analysis of the species’ nestlings was done to determine their diet. The nestling faecal samples were collected during the breeding season of 2019 in the Tamentout deciduous forest in the region of Babors’ Kabylia (north-east Algeria). The faecal samples analysis allowed us to count 686 individuals belonging to 39 different prey taxa. They belong to two arthropods classes and six orders. Insects (95.4%) were more dominant compared with spiders (4.96%). Beetles were most diverse, with 22 prey taxa and 293 individuals. Dermaptera (earwigs) were represented by only two prey taxa and 265 individuals, with the European Earwig Forficula auricularia recorded 253 times. A correlation was also found between the prey sizes and energy intake. Costello’s charts indicated five potential prey including Forficula auricularia, Oxythyrea funesta and Anthaxia sp. were the most consumed. The niche breadth calculation (0.017) revealed that the Algerian Nuthatch specialises on some prey items such as Forficula auricularia to feed its nestlings. The most prized prey species had sizes between 14.5 mm and 19 mm, Forficula auricularia has a size of 15 mm.

ROBBER FLIES (DIPTERA: ASILIDAE) AS PREDATORS OF HARVESTER ANT WORKERS (HYMENOPTERA: FORMICIDAE: POGONOMYRMEX) IN EASTERN NEW MEXICO AND WEST TEXAS

Three species of robber flies (Asilidae) are recorded as preying on workers of Pogonomyrmex harvester ants in eastern New Mexico and western Texas: Cerotainiops abdominalis, Saropogon combustus, and Saropogon pritchardi. Of 379 prey records for C. abdominalis, 66% were Pogonomyrmex workers. Two species of Saropogon were collected in association with a large number of harvester ant workers: S. combustus (40% of 263 prey records) and S. pritchardi (94% of 288 prey records). All three species show a statistical preference for Hymenoptera, specifically for harvester ant workers, and avoidance of Diptera, Hemiptera, Lepidoptera, and Orthoptera prey. A brief review of invertebrate predators of Pogonomyrmex workers is given, with emphasis on asilid predators. For the three asilid predators mentioned in the article, seasonality, observed behaviors, and a list of known prey taxa are included.

Paleoecology of naticid–molluscan prey interaction during the Late Jurassic (Oxfordian) in Kutch, India: evolutionary implications

AbstractWe document and quantify one of the oldest predator–prey interactions between naticid gastropods and molluscan prey, on the basis of drill holes in shells, from the Late Jurassic (Oxfordian) beds of Kutch, western India. Previously, many workers recorded naticid-like drill holes on prey taxa from the Triassic and the Jurassic, but in the absence of associated naticid body fossils, they remained equivocal.The present gastropod community is dominated by turritellines (98% of the sample) that form the turritelline-dominated assemblage, and the naticid drilling predation is restricted almost entirely to turritellines among gastropods. Confamilial naticid predation takes place occasionally. Within the bivalve community, corbulids and nuculids are most abundant and are drilled more often than other taxa. These observations indicate that prey selection was opportunistic and based solely on availability. Drilling intensities at both assemblage and lower taxon levels are low. Behavioral stereotypy of naticid predation in some cases is moderately high.Turritellines are often the preferred prey of naticid gastropods since the late Early Cretaceous. These two groups form a recurrent association reflecting prey–predator interaction. Here we suggest that both turritellines and naticids evolved during the Jurassic, and the prey–predator interaction between them was established shortly thereafter. Among bivalves, corbulids also became important prey of naticids in the same spatiotemporal framework. Corbulids are older than naticids and first appeared during the Middle Jurassic. After their first encounter with naticids, corbulids evolved conchiolin layers within the valves to resist predation.

Diet composition and prey choice by the Great Grey Shrike Lanius excubitor during the non-breeding period: comparing two methods of diet analysis

ABSTRACT Capsule The diet of the Great Grey Shrike Lanius excubitor during the non-breeding period was assessed using analysis of pellets and larders. The two methods gave different results but together showed a preference for voles, crickets and dung beetles. Aims To describe the diet composition of the Great Grey Shrike based on analyses of the contents of pellets and larders; to compare the two methods, and to compare prey taken in relation to its local availability. Methods The research was carried out during the non-breeding period of the Great Grey Shrike in an agricultural landscape of east-central Poland in 2014–2018. The diet was assessed through the analysis of the contents of larders and regurgitated pellets. The abundance of potential prey was assessed with pitfall traps for invertebrates and live traps for small mammals. Results In larders, the ratio of vertebrates to invertebrates was 34.3 : 65.7 (n = 528 prey items), with Orthoptera, Coleoptera and Rodentia predominant. In pellets, the ratio was 64.6 : 35.4 (n = 237 prey items in 155 pellets), with Rodentia and Coleoptera being most numerous. The proportions of the most frequently found prey taxa differed significantly between the two methods of diet analysis. In relation to potential prey availability, Great Grey Shrikes showed a preference for Common Voles Microtus arvalis but seemed to avoid mice Apodemus spp. and Diptera. The greatest discrepancies between the methods were for Coleoptera, Lepidoptera and Orthoptera. Conclusion The results of the pellet and larder analyses differed, mainly because of the large number of Orthoptera found in the larders; shrikes can use them to mark their territories and so they may remain uneaten. Both analytical methods should be used simultaneously to determine the diet composition.

Summer diet of juvenile lake sturgeon reintroduced into the Genesee and St. Regis Rivers, New York USA

The restoration of threatened species involves understanding multiple aspects of the life history and ecology of the target species. One important consideration in the restoration of threatened species is feeding ecology. We examined the summer diet of reintroduced juvenile lake sturgeon (Acipenser fulvescens) in the Genesee (n = 119, ages 1 and 2) and the St. Regis rivers (n = 40, ages 1, 2, 5, 6, and 7) of New York State, USA, in the summer of 2005. The most common taxa consumed were Diptera (88% of prey biomass) in the Genesee River and Ephemeroptera (35% of prey biomass) and Diptera (29%) in the St. Regis River. Diptera: (Chironomidae) was the major prey taxon in both benthic communities. Selectivity analysis showed a positive selection of Diptera by Genesee River lake sturgeon and an avoidance of Diptera by St. Regis River lake sturgeon. The St. Regis River lake sturgeon showed avoidance of Coleoptera, but positive selection of Ephemeroptera, Trichoptera, and Oligochaeta. Results indicate that the reintroduced juvenile lake sturgeon are growing and successfully finding prey in these two rivers and appear to actively select specific prey types.

Capturing shell-crushing by large mobile predators using passive acoustics technology

Durophagy (shell-crushing) is a predatory mode that has evolved across numerous marine taxa from relatively sessile crustaceans to large and highly mobile fishes and mammals. Despite its preponderance in the marine environment, the ecology of durophagy (i.e., dynamics and spatiotemporal distribution) remains poorly understood especially for highly mobile species, limiting our ability to quantify their predatory effects on benthic communities. Here, we used passive acoustics (i.e., remote monitoring of underwater sounds with acoustic recorders) to characterize consumption of hard-shelled mollusk prey by a model predator, the whitespotted eagle ray (Aetobatus narinari). Acoustic recordings were made in captivity for 434 total prey items, spanning eight species of hard-shelled mollusks (1 bivalve, 7 gastropods). For all prey types, consumption sequences were generally characterized by an initial high-energy signal (Sound Pressure Level > 160 dB re 1μPa), presumably associated with shell failure, followed by numerous additional signals of lesser energy as prey was further fractured and winnowed by the predator. Fracture events were short-lived (<0.1 s) with peak frequencies ranging from 3.1 to 5.0 kHz, depending on prey type. Statistical analyses showed capacity to distinguish between the two dominant prey types offered (hard clam, Mercenaria mercenaria and banded tulip, Cinctura lilium) based on processing time, the number of fractures, as well as using a suite of energy and spectral features associated with these acoustic signals. Importantly, we noted that the directionality of these relationships (i.e., relative differences in signals between prey types) can change depending on the chronological location within a consumption sequence and the amount of data analyzed (e.g., first fracture event vs. all fracture event), which may present analytical challenges. Additionally, in situ simulation of fracture events in the target environment suggested events could be detected above ambient noise out to 100 s of m. To our knowledge, this is the first attempt to both quantify and classify durophagy using passive acoustics. We recommend that future studies conduct extensive testing in controlled and target environments to build robust data sets capable of supporting feature extraction as well as detection-classification schemes via machine-learning. Lastly, collaborations with biomechanical scientists are suggested to facilitate a better understanding of the mechanisms driving acoustic variation of shell fracture across prey taxa.

Using DNA metabarcoding to investigate diet and niche partitioning in the native European otter (Lutra lutra) and invasive American mink (Neovison vison)

In the UK, the native European otter (Lutra lutra) and invasive American mink (Neovison vison) have experienced concurrent declines and expansions. Currently, the otter is recovering from persecution and waterway pollution, whereas the mink is in decline due to population control and probable interspecific interaction with the otter. We explored the potential of DNA metabarcoding for investigating diet and niche partitioning between these mustelids. Otter spraints (n = 171) and mink scats (n = 19) collected from three sites (Malham Tarn, River Hull and River Glaven) in northern and eastern England were screened for vertebrates using high-throughput sequencing. Otter diet mainly comprised aquatic fishes (81.0%) and amphibians (12.7%), whereas mink diet predominantly consisted of terrestrial birds (55.9%) and mammals (39.6%). The mink used a lower proportion (20%) of available prey (n = 40 taxa) than the otter and low niche overlap (0.267) was observed between these mustelids. Prey taxon richness of mink scats was lower than otter spraints and beta diversity of prey communities was driven by taxon turnover (i.e. the otter and mink consumed different prey taxa). Considering otter diet only, prey taxon richness was higher in spraints from the River Hull catchment and beta diversity of prey communities was driven by taxon turnover (i.e. the otter consumed different prey taxa at each site). Studies using morphological faecal analysis may misidentify the predator as well as prey items. Faecal DNA metabarcoding can resolve these issues and provide more accurate and detailed dietary information. When scaled up across multiple habitat types, DNA metabarcoding should greatly improve future understanding of resource use and niche overlap between the otter and mink.

Do predators react differently to dangerous and larger prey? The case of a mygalomorph generalist spider preying upon insects

Prey morphology and size are known to influence a predator’s decision to attack and consume particular prey; however, studies that evaluate both traits simultaneously are uncommon. Here, we first described the trophic niche in the mygalomorph spider Paratropis sp. These spiders have a narrow trophic niche and feed mainly on sympatric species such as larvae of lepidopterans and of beetles such as carabids, passalids and scarabeids. Second, we evaluated the effect of prey taxon and size on acceptance and immobilization duration, and built an ethogram of the predator’s behaviors. For each prey taxa, we offered large (approximately same size than the spider) and small larvae (approximately half of the size of the spider) of the aforementioned prey. We classified carabid beetle larvae as the most dangerous prey because of their sharp mandibles and predatory habits, followed by scarabeid larvae; lepidopteran and passalids larvae were considered to be non-dangerous prey. We did not find a significant effect of prey taxon or size on spiders’ acceptance. Prey size did not affect the time invested on each behavioral category, but prey taxon did. Moreover, although spiders used a similar strategy for capturing prey, they spent more time biting carabid larvae than other prey. Our results suggest that, at least in our study area, prey that are dangerous or the predator’s size do not seem to affect Paratropis sp. acceptance per se, but can cause the predator to change the time budget allocated to each behavior.

Ancient dog diets on the Pacific Northwest Coast: zooarchaeological and stable isotope modelling evidence from Tseshaht territory and beyond

Domestic dogs are frequently encountered in Indigenous archaeological sites on the Northwest Coast of North America. Although dogs depended on human communities for care and provisioning, archaeologists lack information about the specific foods dogs consumed. Previous research has used stable isotope analysis of dog diets for insight into human subsistence (‘canine surrogacy’ model) and identified considerable use of marine resources. Here, we use zooarchaeological data to develop and apply a Bayesian mixing model (MixSIAR) to estimate dietary composition from 14 domestic dogs and 13 potential prey taxa from four archaeological sites (2,900–300 BP) in Tseshaht First Nation territory on western Vancouver Island, British Columbia, Canada. Two candidate models that best match zooarchaeological data indicate dogs predominantly consumed salmon and forage fish (35–65%), followed by nearshore fish (4–40%), and marine mammals (2–30%). We compared these isotopic data to dogs across the Northwest Coast, which indicated a pronounced marine diet for Tseshaht dogs and, presumably, their human providers. These results are broadly consistent with the canine surrogacy model as well as help illuminate human participation in pre-industrial marine food webs and the long-term role of fisheries in Indigenous economies and lifeways.

A real-time PCR assay to detect predation by spiny dogfish on Atlantic cod in the western North Atlantic Ocean.

Conventional observations show spiny dogfish (Squalus acanthius Linnaeus) rarely eat Atlantic cod (Gadus morhua Linnaeus; 0.02% of stomachs) in the northwestern Atlantic Ocean. Critics express concern that digestion may limit species‐level prey identification, and with recovery from overfishing, dogfish populations may be suppressing cod by competition or predation. This study applied a real‐time PCR TaqMan assay to identify cod in dogfish stomachs collected by cooperating fishing boats during normal trawling operations (May 2014–May 2015; Gulf of Maine, Georges Bank). Conventional methods observed 51 different prey taxa and nearly 1,600 individual prey items, but no cod were observed. Cod DNA was detected in 31 (10.5%) of the dogfish stomachs, with a higher percentage of these from the homogenate of amorphous, well‐digested prey and stomach fluids (20 stomachs or 65%) than from discrete animal tissues (11 stomachs or 35%). Re‐examination of photographs of these 11 tissue samples revealed one whole, partially digested fish that could be recognized in hindsight as cod. Cod DNA was observed in dogfish stomachs year round: in January (1 of 1 trip), February (1 of 1), May (1 of 3), June (0 of 1), July (3 of 4), August (1 of 2), and October (3 of 3). Although these data suggest higher interaction rates between dogfish and cod than previously observed, addressing the population consequences of this predator–prey relationship requires a robust sampling design, estimates of digestion rates by dogfish to account for complete degradation of DNA sequences, and consideration for dogfish scavenging during fishing operations.

Habitat utilization and feeding ecology of small round goby in a shallow brackish lagoon

We examined small-scale distribution and feeding ecology of a non-native fish species, round goby (Neogobius melanostomus (Pallas, 1814)), in different habitats of a coastal lagoon situated in the south-western Baltic Sea. First observations of round goby in this lagoon were reported in 2011, 3 years before the current study was conducted, and information on this species’ basic ecology in different habitats is limited. We found that mainly juvenile round gobies are non-randomly distributed between habitats and that abundances potentially correlate positively with vegetation density and thus structural complexity of the environment. Abundances were highest in shallower, more densely vegetated habitats indicating that these areas might act as a refuge for small round gobies by possibly offering decreased predation risk and better feeding resources. Round goby diet composition was distinct for several length classes suggesting an ontogenetic diet shift concerning crustacean prey taxa between small (≤ 50 mm total length, feeding mainly on zooplankton) and medium individuals (51–100 mm, feeding mainly on benthic crustaceans) and another diet shift of increasing molluscivory with increasing body size across all length classes. Differences in round goby diet between habitats within the smallest length class might potentially be related to prey availability in the environment, which would point to an opportunistic feeding strategy. Here, we offer new insights into the basic ecology of round goby in littoral habitats, providing a better understanding of the ecological role of this invasive species in its non-native range, which might help to assess potential consequences for native fauna and ecosystems.

Diet of albacore Thunnus alalunga from the waters of Mauritius (western Indian Ocean) inferred from stomach contents and fatty acid analysis

The diet of albacore Thunnus alalunga from their spawning ground in the waters of Mauritius was investigated. The stomach contents of 249 albacore individuals, caught by industrial longliners and artisanal fishers, was analysed, and the dominant prey taxa were selected for lipid and fatty acid (FA) analysis. The FA profiles of prey were compared with those of liver tissue of spawning-capable and post-spawning female albacore, using multivariate analysis. Whereas stomach content analysis identified cephalopods and crustaceans as the dominant prey items in number, FA-profile analysis identified crustaceans and fishes as the most-frequently consumed prey of post-spawning female albacore. In contrast, the FA profiles of spawning-capable albacore and those of prey showed very low similarity. Analysis of the prey suggests that although cephalopods, crustaceans and fishes could all provide albacore with the required lipids and FAs, cephalopod prey seem to be less desirable owing to their lower energy content (i.e. low in total lipid, triacylglycerol, 16:0, 18:0 and 18:1ω9). Instead, the most beneficial food appeared to be locally available fishes, which are more energy-rich and have a higher docosahexaenoic acid/ eicosapentaenoic acid ratio. These results provide new information on the trophic ecology of albacore, promote our understanding of the importance of prey type for successful reproduction of albacore, and highlight the advantages of FA profiling to study diet.

SquamataBase: a natural history database and R package for comparative biology of snake feeding habits.

Public databases in taxonomy, phylogenetics and geographic and fossil occurrence records are key research tools that provide raw materials, on which broad-scale analyses and synthesis in their respective fields are based. Comparable repositories for natural history observations are rare. Publicly available natural history data on traits like diet, habitat and reproduction are scattered across an extensive primary literature and remain relatively inaccessible to researchers interested in using these data for broad-scale analyses in macroecology and macroevolution. In this paper, I introduce SquamataBase, an open-source R package and database of predator-prey records involving the world’s snakes. SquamataBase facilitates the discovery of natural history observations for use in comparative analyses and synthesis and, in its current form, contains observations of at least 18,304 predator individuals comprising 1,227 snake species and at least 58,633 prey items comprising 3,231 prey taxa. To facilitate integration with comparative analysis workflows, the data are distributed inside an R package, which also provides basic functionality for common data manipulation and filtering operations. Moving forward, the continued development of public natural history databases and their integration with existing digitisation efforts in biodiversity science should become a priority.

Diet composition of starry smooth‐hound Mustelus asterias and methodological considerations for assessing the trophic level of predatory fish

The stomach contents of 640 starry smooth-hound Mustelus asterias from the north-east Atlantic were examined. The diet was dominated by crustaceans (98.8% percentage of index of relative importance, %IRI), with the two main prey species being hermit crab Pagurus bernhardus (34% IRI) and flying crab Liocarcinus holsatus (15% IRI). Ontogenetic dietary preferences showed that smaller individuals [20-69 cm total length (LT ) n = 283] had a significantly lower diversity of prey than larger individuals (70-124 cm LT , n = 348); however, 18 prey species were found exclusively in smaller individuals and eight prey taxa were found exclusively in larger individuals. Larger commercially important brachyurans such as edible crab Cancer pagurus and velvet swimming crab Necora puber were more prevalent in the diet of larger individuals. Specimens from the North Sea ecoregion had a lower diversity of prey types for a given sample size than fish from the Celtic Seas ecoregion. Whilst cumulative prey curves did not reach an asymptote, this was primarily due to the high taxonomic resolution utilized and 95% of the diet was described by just seven crustacean taxa. The trophic level (TL) was calculated as 4.34 when species-level prey categories were used. This fine-scale taxonomic resolution resulted in a TL estimate close to a whole level above that estimated using wider taxonomic groupings. This large bias has important methodological implications for TL studies based on categorized prey data, particularly those of predatory fish.

Prey selectivity, functional response, and population growth of Asplanchna girodi de Guerne (Rotifera) fed four different brachionid prey

ABSTRACTWe determined numerical response, functional response, and prey selection by the predator Asplanchna girodi using 4 brachionid rotifer species, varying in size and lorica spines. We hypothesized that the consumption by the predators and thus population growth rates would be highest on prey with small spines compared with those with long spines. Data on the numerical response study showed that the population growth patterns of A. girodi were significantly influenced by prey species and density. With greater prey availability, the populations of the predator reached higher densities. At any given prey density, population densities of A. girodi were higher when feeding on Plationus patulus and Brachionus angularis than on B. rubens and B. havanaensis. The highest numbers of males were produced on diets of B. havanaensis and P. patulus. The rate of population increase ranged between 0.2 and 0.4 d−1 and was highest when feeding on a diet of P. patulus. A. girodi showed type II functional response for all the tested prey species. Among the 4 prey taxa tested, A. girodi showed the highest preference for B. angularis, regardless of its density. By contrast, it avoided B. rubens and P. patulus completely. These observations corroborate our hypothesis and suggest that prey morphology is an important determinant in prey selection by nonvisual predators such as Asplanchna.

Breeding behaviour and diet of the Crowned Eagle Stephanoaetus coronatus in western Tanzania

The aim of the current study was to reveal the breeding ecology of Crowned Eagles in western Tanzania through constant daytime monitoring. The breeding circumstances of three resident pairs in the focal study area suggest that the breeding cycle of the species is seasonal, because they lay eggs in the dry season, so that fledging occurs in the rainy season. One pair brought a total of 88 prey items (a minimum of 80 prey individuals) during the breeding period from nest-making to the point at which the nestling was about to fledge at 106 days old. Prey animals comprised three vertebrate taxa (mammal, reptile and bird), of which mammals dominated, ranging over primates, rodents, carnivores, hyraxes and bovids. Diversity of prey taxa increased in the later stage of the nestling period. As well as breeding periodicity and prey selectivity, I describe details of some novel behaviours related to breeding ecology of the species, such as nest material delivery, copulation, feeding behaviour, unilateral eye closure, alert behaviour and defensive behaviour.

Primates are an important food resource for leopards (Panthera pardus) in Mahale, Tanzania

AbstractLeopard diets in the Kasoje area of the Mahale Mountains National Park, Tanzania, were analysed by inspecting prey remains in 256 scats. This area is unique as leopard density is high despite a relatively low density of medium‐sized ungulates, regarded as the most preferred prey of leopards. At least eleven prey mammal species were confirmed in the scats. Small prey mammals up to 10 kg comprised 91.4% of the relative biomass consumed; the mean prey biomass in each scat was 7.6 kg. Blue duiker (31.2%) was the most dominant prey species, followed by the red colobus (29.2%), semi‐terrestrial Cercopithecinae (the vervet monkey and yellow baboon combined) (10.5%) and the red‐tailed monkey (9.9%). At the order level, the most consumed prey taxon was Primates (53.8%), followed by Cetartiodactyla (39.6%) and Rodentia (5.8%). Among primates, the blue monkey was the most preferred prey species, followed by the red colobus and semi‐terrestrial Cercopithecinae. High consumption of primates is a unique characteristic of the leopards in Mahale. This trend exemplifies the flexibility of leopards in their choices of prey, and such flexibility may be one of the underlying reasons for leopards exhibiting the broadest global distribution among all wild felid species.

Diet of Glossogobius callidus (Teleostei: Gobiidae) in freshwater impoundments in the Sundays River Valley of the Eastern Cape, South Africa

Despite the high abundance of the gobiid fish Glossogobius callidus in many freshwater ecosystems in South Africa, very few studies have assessed the biology and ecology of the species. Here, we investigated the diet of G. callidus populations sourced from Sundays River irrigation ponds. A total of 571 fish grouped into two size classes (TL, range ± SD: juveniles of 20–60 ± 45 mm; adults of 61–140 ± 85 mm) were sampled by seine netting; prey items were removed from the guts and identified and sorted to obtain dietary information for each prey group. Of the examined guts, 97% contained prey comprising 17 taxa within 10 taxonomic groups. Teleosts were identified to species level, whereas most dietary components were identified to a broad taxonomic group. Aquatic invertebrates were the most important component of the diet of G. callidus, but the index of relative importance (%IRI) of dominant invertebrate taxa varied according to ontogenetic stage of G. callidus and season. Prey taxa included: Diptera, Hemiptera, Trichoptera, Odonata, Cladocera, Copepoda, Hydracarina, Amphipoda, Mollusca and Teleostei. Dipteran prey taxa were consistently encountered in both size classes and across all seasons. G. callidus can therefore be regarded as a generalist invertivore.

Novel vs. Traditional Approaches to Sampling Seabird Diet: Nest and Pellet Analysis of Brandt's Cormorants (Phalacrocorax penicillatus)

Diet of the Brandt's Cormorant (Phalacrocorax penicillatus) breeding population on Alcatraz Island, California, USA was determined for 2014-2016 using two sampling methods. Regurgitated pellets and complete nests were collected, once all chicks had left colonies, to reduce disturbance to nesting birds. Results identified 25 prey taxa including 23 teleost fishes and two cephalopods. Diet was dominated by northern anchovy (Engraulis mordax) and speckled sanddab (Citharichthys stigmaeus), with plainfin midshipman (Porichthys notatus), sole spp. (Pleuronectidae), and sculpin spp. (Cottidae) rounding out the top five abundant species. Comparison of diet by sample type yielded similar results in terms of prey species composition, but total diet differed between the two samples due to rare prey items being more prevalent in nest samples. Determining cormorant diet using a combination of pellet and nest samples is a novel approach with the potential to provide a better representation of prey consumed during the full breeding period (up to 6 months for cormorants), and similar methods may be informative for other seabirds that produce pellets. In contrast, diet determined from pellets alone may only represent a short time period just prior to collection, as pellets are often blown away by strong winds or disintegrate through trampling and/or exposure to the elements in open seabird breeding colonies.