Natural Prey Items Research Articles

Responses to prey chemical cues in wild-caught, adult gopher snakes (Pituophis catenifer).

Surface chemical cues from prey elicit elevated levels of tongue-flicking and striking behavior in many species of snakes and lizards. These responses are mediated by the vomeronasal system, and they may even occur in the absence of other sensory cues. How individuals of a species respond to prey chemical cues can reflect developmental, ecological, and evolutionary processes. Our focus in this study was ecologically based, and involved testing whether levels of chemosensory responding reflect the putative relative intake of prey types in nature. We tested 11 wild-caught adult gopher snakes (Pituophis catenifer) for their chemosensory responses, namely tongue flicking, in response to surface chemicals of natural prey items (rodent and bird) and to two control stimuli (distilled water and hexane). On average the snakes had significantly higher rates of tongue flicking toward prey cues than to control stimuli (p = .001). Responses to rodent and bird surface chemicals did not significantly differ from each other (p = .35). Tongue-flick responses to rodent surface chemicals were significantly higher than to both water and hexane (ps < .01), while responses to bird surface chemicals were significantly higher than to water (p < .05) but not to hexane (p = .12). (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Testing the Effects of Prey Type on the Life History and Population-Level Parameters of Chrysoperla externa (Neuroptera: Chrysopidae).

Green lacewings are valuable predators, utilized in augmentative biological control against various agricultural pests. However, further studies are required to comprehend the performance of these predators when consuming natural prey. We investigated the capacity of Chrysoperla externa (Hagen) to utilize the following three distinct prey types: the pupae of the coffee leaf miner Leucoptera coffeella (Guérin-Mèneville & Perrottet), the eggs of the sugarcane borer Diatraea saccharalis (F.), and the eggs of the Mediterranean flour moth Ephestia kuehniella (Zeller). The first two of these species are naturally occurring prey found in field crops, while the last serves as a factitious prey species for the mass rearing of natural enemies. We hypothesized that the type of prey would differentially affect the life history and population-level parameters of C. externa. Laboratory experiments were conducted to compare the pre-imaginal survival and developmental times, adult longevity and reproduction, and population growth of C. externa when larvae were provided with each of the three prey items. Results indicated that C. externa utilized the two natural prey items, L. coffeella pupae and D. saccharalis eggs, for its development, reproduction, and population growth. However, larvae developed significantly faster and females exhibited higher reproductive parameters, including fecundity and daily oviposition, when consuming the factitious prey, E. kuehniella eggs. This resulted in a higher intrinsic rate of population increase, as well as shorter times for the population to double in size. Understanding the population dynamics of C. externa when consuming different prey items is crucial for optimizing their utilization in augmentative biological control programs.

Natal Origin Differentiation Using Eye Lens Stable Isotope Analysis

AbstractNatal origin determination can be critical to understanding the movement, recruitment, and stock discrimination of fish populations. We investigated the utility of eye lens stable isotope analysis as a natural marker to determine natal origins, specifically the differentiation of stocked versus naturally reproduced individuals. We compared isotopic values for stocked and naturally reproduced Rainbow Trout Oncorhynchus mykiss in the North Platte River (Wyoming, USA) and found that the metabolically inert core of the eye lens retained hatchery feed values as the fish grew poststocking. The stable isotope values of eye lens cores from stocked Rainbow Trout were &gt;15‰ higher for δ34S and &gt;4‰ higher for δ13C than naturally reproduced fish. The values for δ15N proved to be a less useful indicator for natal origin than sulfur and carbon. These high carbon and sulfur isotopic values were retained in the core, despite subsequent lens layers showing a dietary shift to natural prey items poststocking. Rainbow Trout formed over 10 layers at age 0, decreasing to an estimated one to two layers during subsequent years. Eye lens stable isotope analysis represents an additional tool for researchers and managers to use natural isotopic markers to accurately assess natal origins and hatchery contributions to fish populations.

The diet of coyotes and red foxes in Southern New York

Coyotes (Canis latrans) and red fox (Vulpes vulpes) are both generalist predators presently found in the Northeastern United States. This study aimed to identify major prey items of both species in suburban New York, investigate consumption of anthropogenic resources, and examine seasonal changes in diet. Scat samples were collected from 2017 to 2018 for coyotes, and from 2011 to 2012 for red fox. Hairs, feathers, bone fragments and other scat components were classified by comparison with reference collections. Logistic regression was used to determine whether season or location predicted the presence of various food items. The most common food items for coyotes were white-tailed deer (Odocoileus virginianus), found in 54.2% of samples, and cricetid rodents, found in 16.9% of samples. For red fox the most common food items were birds, found in 39% of samples, and cricetid rodents, found in 37.8% of samples. Anthropogenic waste appeared in 11.9% of coyote scat samples and made up 1.3% of the total weight of items recovered from samples. No anthropogenic items were found in red fox scat, nor were remains from threatened piping plovers (Charadrius melodus), known to breed in the study area. Seasonal changes in diet were not detected for either species. Overall our results show that coyotes and red fox in suburban areas of Southern New York are persisting primarily on natural prey items, and not being subsidized by anthropogenic food sources.

Diet Breadth Mediates the Prey Specificity of Venom Potency in Snakes.

Venoms are best known for their ability to incapacitate prey. In predatory groups, venom potency is predicted to reflect ecological and evolutionary drivers relating to diet. While venoms have been found to have prey-specific potencies, the role of diet breadth on venom potencies has yet to be tested at large macroecological scales. Here, using a comparative analysis of 100 snake species, we show that the evolution of prey-specific venom potencies is contingent on the breadth of a species’ diet. We find that while snake venom is more potent when tested on species closely related to natural prey items, we only find this prey-specific pattern in species with taxonomically narrow diets. While we find that the taxonomic diversity of a snakes’ diet mediates the prey specificity of its venom, the species richness of its diet was not found to affect these prey-specific potency patterns. This indicates that the physiological diversity of a species’ diet is an important driver of the evolution of generalist venom potencies. These findings suggest that the venoms of species with taxonomically diverse diets may be better suited to incapacitating novel prey species and hence play an important role for species within changing environments.

Bait-subsidized diets and their effects on ovigerous North American lobsters (Homarus americanus)

Ovigerous American lobsters (Homarus americanus) display a protracted period of ovary maturation and maternal care when incubating their eggs, potentially influencing offspring fitness. Lobsters consume a wide range of food items; however, trap bait may comprise a larger proportion of their diet in some fished areas compared to non-fished areas, and the long-term consequences of a bait-based diet remain largely unexplored in lobsters. We tested the hypothesis that disproportionate amounts of bait in the diets of pre-ovigerous females affect the quality of their ovaries and eggs. We held pre-ovigerous lobsters (n = 29) over a period of ~ 300 days (range = 270–378) and fed them diets of herring bait, natural prey items (crab, mussel, urchin, macroalgae), or a combination of both diet types. Nutritional status, measured as biweekly blood indices and total glucose levels, suggest differences between lobsters fed a natural or combination diet and lobsters fed a bait-based diet (ANOVA; P < 0.05). We found that bait diets contained more protein (58.5%) and lipids (31.6%) compared to natural diets (34.5 and 13.2%, respectively) and lipid levels in ovaries and eggs significantly correlated with each other for all treatments (r = 0.76, n = 15, P = 0.028). Histopathological analysis indicates that ovaries contained more variable maturation in starved lobsters or those fed with bait, with some animals showing delayed gonad maturation. Results suggest that a varied diet promotes the overall fitness of ovigerous lobsters and the associated reserves that are used for ovarian development and subsequent oocyte formation.

Nutritional physiology of mahi-mahi (Coryphaena hippurus): Postprandial metabolic response to different diets and metabolic impacts on swim performance

Migratory pelagic fish species, such as the mahi-mahi (Coryphaena hippurus), must balance numerous metabolic demands simultaneously in order to survive in a challenging oceanic environment. Energetic support for such demands comes from a variety of natural prey items in the wild and can come from manufactured pelletized feed in captivity. This study quantified postprandial metabolism, commonly referred to as specific dynamic action (SDA), over time in adult mahi-mahi (706±25g; 38±0.7cm FL) in response to satiation feeding using three different natural and manufactured diets. Results indicate that during satiation feeding the amount of food ingested is dictated by energy content rather than prey mass, regardless of moisture content of the diet. Ingested meal energy did not differ significantly across groups (473±45kJ), nor did the duration of SDA (36±2.1h). Satiation feeding levels ranged from 2.9–16.2% bodyweight depending on the diet. Peak SDA and SDA magnitude were both significantly decreased in response to dry pelletized diet compared to the natural forage diets, despite equivalent energy consumption. Swim performance and maximum metabolic rate were not impacted significantly in satiation fed fish compared to unfed fish, supporting the evidence that mahi-mahi are able to maintain multiple metabolic demands at one time without compromising performance.

Artisanal fishing of spiny lobsters with gillnets — A significant anthropic impact on tropical reef ecosystem

Artisanal fishing activity with gillnets to capture the spiny lobster is a common practice along the coastal reefs of Brazil. This research aims to understand the impact that this artisanal fishing practice is having on the coastal reef systems analysing its associated fauna (bycatch) and the stock of the target species Panulirus echinatus. The study compared an area which was subjected to intense gillnet fishing against one were the practice was absent. The analysis of target species using nocturnal visual census demonstrated a significantly higher number of P. echinatus at the site where gillnet use was virtually absent within three sampled habitats, fringe, cave and soft bottom. The analysis of bycatch species from artisanal fishermen’s gillnet landings recorded 4 lobster species and 10 crab species. These decapod species play an important ecological role as detritivores, herbivorous and first consumers within the reef ecosystem as well as being natural prey items for several reef fishes. The study concludes that this non-discriminatory fishing technique impacts directly on populations of P. echinatus, P. argus and P. laevicauda as well as other lobster and crab species which in-turn indirectly affects the ecological role of the tropical coastal reefs of Brazil.

Do the intestinal microbiotas differ between paddlefish (Polyodon spathala) and bighead carp (Aristichthys nobilis) reared in the same pond?

A study was conducted to compare the intestinal microbial compositions of two fish species with similar feeding strategy; paddlefish (Polyodon spathala) and bighead carp (Aristichthys nobilis) reared in the same pond. Age-0 paddlefish and bighead carp with mean average body lengths of 43·39 ± 2·78 and 19·33 ± 3·68 cm, respectively, were reared with natural prey items in the same pond (20 m(2)). After 30 days of rearing, the intestinal microbiota of the two fish species was assessed by pyrosequencing of 16S rRNA genes. Interestingly, deviations were observed in the microbial communities of the two fish species according to the alpha- and beta-diversity measurements and detrended correspondence analysis (DCA). Shannon diversity (P = 0·015) and Pielou.evenness (P = 0·035) revealed significant lower diversity of the intestinal microbiota of paddlefish. Moreover, different core intestinal microbiota was noticed in the two fish species. Proteobacteria (57·3%), Firmicutes (11·9%), Fusobacteria (8·9%), Planctomycetes (7·3%), Actinobacteria (6·0%) and Verrucomicrobia (3·2%) were detected in bighead carp, while the dominant phyla in paddlefish intestines were Bacteroidetes (37·0%), Fusobacteria (35·1%), Firmicutes (14·8%) and Proteobacteria (12·6%). Our results revealed that the intestinal microbiota differed between paddlefish and bighead carp reared in the same pond when fed similar nature food. The potential host factors, such as the genetic background, gut histology and physiology are assumed to be involved in the intestinal bacterial compositions. Considering the similar feeding strategy of paddlefish and bighead carp, this study presents basic knowledge for evaluation of the importance of host factors (genetic background and gut anatomy) on intestinal microbial composition.

Eating between the lines: functional feeding response of bonnetheads (Sphyrna tiburo)

Mobile mesopredators can have strong influences in the structuring of marine food webs in shallow coastal ecosystems. Few quantitative estimates of the effects of predation on prey populations by highly mobile mesopredators exist, yet they are necessary to evaluate the impact mesopredators have on prey resources. Quantifying a predator’s functional response provides valuable information on how a predator’s per capita consumption rate of prey can influence community structure and prey populations. We examined the functional response of bonnetheads (Sphyrna tiburo) to one of its few natural prey items brown shrimp (Farfantepenaeus aztecus) to determine if per capita feeding rates would increase with increases in prey density. We simulated natural conditions in outdoor mesocosms and offered live prey at varying densities. The functional response of a predator can take one of three forms: linear (type I), rise to an asymptote (type II), and a sigmoid shape (type III). Bonnetheads consumed prey proportional to prey density and demonstrated a response that was in between a type I (R2 = 0.847, p < 0.01) and type II (R2 = 0.877, p < 0.01) functional response. Bonnetheads showed an increased rate of consumption with initial low prey densities but high densities of available prey did not consistently result in increased consumption rates. At the maximum prey density offered, bonnetheads consumed less prey than at intermediate densities. Bonnetheads may not have as strong of an influence on prey populations at high prey densities compared to predation impacts at low densities. Bonnethead per capita feeding rates did not conform to a type I, type II, or type III functional response and our results suggest that bonnetheads follow a functional response continuum more closely. This study highlights the importance and difficulty in understanding the feeding ecology of highly mobile mesopredators.

Mistaken identity? Visual similarities of marine debris to natural prey items of sea turtles

BackgroundThere are two predominant hypotheses as to why animals ingest plastic: 1) they are opportunistic feeders, eating plastic when they encounter it, and 2) they eat plastic because it resembles prey items. To assess which hypothesis is most likely, we created a model sea turtle visual system and used it to analyse debris samples from beach surveys and from necropsied turtles. We investigated colour, contrast, and luminance of the debris items as they would appear to the turtle. We also incorporated measures of texture and translucency to determine which of the two hypotheses is more plausible as a driver of selectivity in green sea turtles.ResultsTurtles preferred more flexible and translucent items to what was available in the environment, lending support to the hypothesis that they prefer debris that resembles prey, particularly jellyfish. They also ate fewer blue items, suggesting that such items may be less conspicuous against the background of open water where they forage.ConclusionsUsing visual modelling we determined the characteristics that drive ingestion of marine debris by sea turtles, from the point of view of the turtles themselves. This technique can be utilized to determine debris preferences of other visual predators, and help to more effectively focus management or remediation actions.

Chemosensory response in stunted prairie rattlesnakes Crotalus viridis viridis

Abstract Rattlesnakes use chemical stimuli in ambush site selection and for relocation of envenomated prey through strike-induced chemosensory searching. Shifts in responsiveness to prey chemicals have been documented in many snakes, and often correlate with prey commonly taken as snakes increase in age and size as well as geographical locations of the species. For instance, neonate rattlesnakes that prey primarily on ectotherms responded most strongly to chemical cues of commonly taken lizard prey, whereas adult rattlesnakes that prey primarily on small mammals responded significantly to chemical cues of commonly taken rodents. In the current study, 11 Prairie Rattlesnakes Crotalus viridis viridis which were classified as large neonates based on measures of snout-vent length (SVL) and body mass, yet chronologically were at or near adulthood, were tested for their responsiveness to chemical extracts of natural and non-natural prey items. Although the snakes had eaten only neonate lab mice (Mus musculus), they responded significantly more to chemical cues of natural prey items and particularly to chemical cues of prey normally taken by subadults (Peromyscus mice and Sceloporus lizard). These results suggest that ontogenetic shifts in responsiveness to natural prey chemical cues are innately programmed and are not based on body size or feeding experience in C. v. viridis. This does not imply, however, that growth and experience are without effects, especially with novel prey or rare prey that have experienced recent population expansion.

Correlations of xanthophylls in catfish fillets, plankton, shad and snails in catfish production ponds in west Alabama

Yellow coloration of catfish fillets has always been a problem. Recently increased consumer scrutiny has brought this to the forefront as a major industry concern. As catfish cannot synthesize xanthophyll, commercial feeds and natural prey items are the initial sources of the yellow color. To better understand the contribution of natural foods, a field study was conducted to identify if there were correlations of yellow fillet and natural productivity under commercial pond conditions. Upon notification from a west Alabama fish processor, yellow catfish fillets and natural organism samples (plankton, shad and snails) were collected from different farm ponds in west Alabama. “Clean” catfish fillets (no unacceptable yellow coloration) and natural organisms were also collected at multiple farms where problematic yellow fillets were not present. In addition to large food items, microorganism samples from the ponds were collected by pumping pond water through two filters (sizes 20μm and 75μm) for a period of 10min. The fillet and field samples were analyzed quantitatively for xanthophyll levels through High-Pressure Liquid Chromatography (HPLC). Results revealed a correlation between xanthophyll level in catfish fillets and in microorganisms (>75μm). Results indicate that natural productivity consumed by gizzard shad and other filter feeders appears to contribute to the xanthophyll levels in catfish fillets.

To Eat or Not to Eat? Debris Selectivity by Marine Turtles

Marine debris is a growing problem for wildlife, and has been documented to affect more than 267 species worldwide. We investigated the prevalence of marine debris ingestion in 115 sea turtles stranded in Queensland between 2006–2011, and assessed how the ingestion rates differ between species (Eretmochelys imbricata vs. Chelonia mydas) and by turtle size class (smaller oceanic feeders vs. larger benthic feeders). Concurrently, we conducted 25 beach surveys to estimate the composition of the debris present in the marine environment. Based on this proxy measurement of debris availability, we modeled turtles’ debris preferences (color and type) using a resource selection function, a method traditionally used for habitat and food selection. We found no significant difference in the overall probability of ingesting debris between the two species studied, both of which have similar life histories. Curved carapace length, however, was inversely correlated with the probability of ingesting debris; 54.5% of pelagic sized turtles had ingested debris, whereas only 25% of benthic feeding turtles were found with debris in their gastrointestinal system. Benthic and pelagic sized turtles also exhibited different selectivity ratios for debris ingestion. Benthic phase turtles had a strong selectivity for soft, clear plastic, lending support to the hypothesis that sea turtles ingest debris because it resembles natural prey items such as jellyfish. Pelagic turtles were much less selective in their feeding, though they showed a trend towards selectivity for rubber items such as balloons. Most ingested items were plastic and were positively buoyant. This study highlights the need to address increasing amounts of plastic in the marine environment, and provides evidence for the disproportionate ingestion of balloons by marine turtles.

Application of a Bioenergetics Model for Hatchery Production: Largemouth Bass Fed Commercial Feeds

AbstractFish bioenergetics models based on natural prey items have been widely used to address research and management questions. However, few attempts have been made to evaluate and apply bioenergetics models to hatchery‐reared fish receiving commercial feeds that contain substantially higher energy densities than natural prey. In this study, we evaluated a bioenergetics model for age‐0 largemouth bass Micropterus salmoides reared on four commercial feeds. Largemouth bass (n ≈ 3,504) were reared for 70 d at 25°C in sixteen 833‐L circular tanks connected in parallel to a recirculation system. Model performance was evaluated using error components (mean, slope, and random) derived from decomposition of the mean square error obtained from regression of observed on predicted values. Mean predicted consumption was only 8.9% lower than mean observed consumption and was similar to error rates observed for largemouth bass consuming natural prey. Model evaluation showed that the 97.5% joint confidence region included the intercept of 0 (−0.43 ± 3.65) and slope of 1 (1.08 ± 0.20), which indicates the model accurately predicted consumption. Moreover model error was similar among feeds (P = 0.98), and most error was probably attributable to sampling error (unconsumed feed), underestimated predator energy densities, or consumption‐dependent error, which is common in bioenergetics models. This bioenergetics model could provide a valuable tool in hatchery production of largemouth bass. Furthermore, we believe that bioenergetics modeling could be useful in aquaculture production, particularly for species lacking historical hatchery constants or conventional growth models.

Effect of strain and selection line on the fecundity of the cyclopoid copepodParacyclopina nanaSmirnov, 1935

AbstractWe studied the effect of strain and selection lineson the fecundity of the cyclopoid copepod Paracyc-lopina nana. We used six strains (HL, YL, BS, SL,TH, TS) and six isofemale lines (including threehigher and three lower fecundity lines). As for theselection of strain, total nauplii production perfemale of SL strain was the highest in the individ-ual culture (231 nauplii per female) and popula-tion growth rate in HL and SL strains showedhigher values than the others in combined culture.For the selection of line, the total nauplii produc-tion per female of HF 2 -2 (high fecundity and sec-ond generation) line was the highest (302 naupliiper female) but those of LF 2 -1 (low fecundity) (80nauplii per female), and LF 2 -3 (46 nauplii perfemale) lines were lower than the others. In F 4 generation, three selected HF 2 -2 line showed thatthe total nauplii production were higher thanthose of three selected LF 2 -3 lines. In the combinedculture on the different selection lines (F 8 ), popula-tion growth rate of two selected high fecunditylines showed higher values than that of the non-selection group and selected low fecundity line.Our results demonstrate that the production ofP. nana can be improved by selection of the linewith high fecundity.Keywords: live feed, copepod, strain, selection,fecundity, Paracyclopina nanaIntroductionSince mariculture is an ever expanding sector ofthe food-producing industry, the improvement ofnovel technologies for the intensification of cul-tures and farming of seaweed and animals arewarranted (Dahms, Gao & Hwang 2007; Camus Z Drillet,Frouel, Sichlau, Jepsen, Hojgaard, Joarder & Hansen2011). Especially the nauplius larvae of copepodsprovide natural prey items for marine invertebrate

Diet Specialization by the Scarlet Kingsnake, Lampropeltis elapsoides (Colubridae)

Based on 34 natural prey items, Lampropeltis elapsoides eats primarily elongate squamates (97%), especially skinks (74%) and colubroid snakes (15%). N o ontogenetic or geographic variation is evident; prey items are swallowed headfirst and average 19% of predator mass. The diet substantially overlaps that of juveniles of some other lampropeltines, including sympatric L. triangulum, but is unusually narrow compared to adults of most other species.

Response of juvenile scalloped hammerhead sharks to electric stimuli

Sharks can use their electrosensory system to detect electric fields in their environment. Measurements of their electrosensitivity are often derived by calculating the voltage gradient from a model of the charge distribution for an ideal dipole. This study measures the charge distribution around a dipole in seawater and confirms the close correspondence with the model. From this, it is possible to predict how the sharks will respond to dipolar electric fields comprised of differing parameters. We tested these predictions by exposing sharks to different sized dipoles and levels of applied current that simulated the bioelectric fields of their natural prey items. The sharks initiated responses from a significantly greater distance with larger dipole sizes and also from a significantly greater distance with increasing levels of electric current. This study is the first to provide empirical evidence supporting a popular theoretical model and test predictions about how sharks will respond to a variety of different electric stimuli.

A Comparison of Black Carp, Redear Sunfish, and Blue Catfish as Biological Controls of Snail Populations

AbstractRedear sunfish Lepomis microlophus and blue catfish Ictalurus furcatus were compared with black carp Mylopharyngodon piceus as potential biological controls for rams‐horn snails Planorbella spp. Comparisons were made with regard to snail size selection, total consumption, and the effects of alternative prey and temperature on consumption rates of two size‐classes for each species, small (≤100 mm total length [TL]) and large (&gt;100 mm TL). Examination of stomach contents revealed that black carp and redear sunfish crush snails, whereas blue catfish do not. Electivity indices showed that large black carp randomly consumed snails from all shell lengths, whereas large redear sunfish avoided snails larger than 13 mm. Large black carp, redear sunfish, and blue catfish consumed commercial feed when provided in conjunction with snails. The largest amount of snail consumption by all fish species occurred at 26°C, and declined slightly as water temperature decreased from 26°C to 12°C. Black carp were the most effective consumers of rams‐horn snails and did not show any preference for a particular size or range of sizes of snails. Redear sunfish consumed significantly fewer snails than black carp but significantly more than blue catfish. In this study, redear sunfish were a better biological control of rams‐horn snails than blue catfish but not as effective as the exotic black carp. However, further studies need to be conducted under natural conditions to determine whether the presence of other natural prey items will affect the selectivity of redear sunfish with respect to rams‐horn snails.

At-sea distribution and behaviour of a surface-feeding seabird, the lesser black-backed gull Larus fuscus, and its association with different prey

The lesser black-backed gull Larus fuscus is a typical surface-feeding seabird with a widespread, patchy distribution in the SE North Sea. During the 1990s, breeding numbers along the German North Sea coast increased exponentially. Analyses of a multiple-year data set revealed changes in the at-sea distribution that seemed to reflect an increase in the numbers of breeding birds. Detailed recordings of feeding and resting behaviour at sea revealed area utilisation by the lesser black-backed gull. Observations at sea and dietary analysis revealed that swimming crabs Liocarci- nus spp. are a major dietary item of this gull species. This natural food source was primarily captured close to the shore; at longer distances from the coast the gulls mainly fed on other natural prey items or discarded fishes from trawlers and avoided competition with other breeding gull species. During July and August 1990 to 1995 L. fuscus abundance was significantly correlated with fishing effort, while in May and June there was no such correlation. Time of day was the main environmental vari- able influencing the gulls' flight activity and indicated an association between activity and availabil- ity of their major natural prey, swimming crabs. Distinct patterns and changes in the at-sea distribu- tion and foraging behaviour of L. fuscus in the SE North Sea reflect anthropogenic and natural influences in their habitats.