Preen oil chemical composition in herring gull Larus argentatus,common gull Larus canus and black-headed gull Chroicocephalus ridibundus confirms their status as two separate genera

Fatty acid and alcohol components of preen oil were determined in three gull species that belong to two systematic genera: herring gull Larus argentatus, common gull Larus canus and black-headed gull Chroicocephalus ridibundus. All gulls were captured in winter, in Gdańsk, Poland. All gulls produced monoesters composed of C₇–C₁₆ saturated fatty acids and C₁₁–C₂₀ saturated alcohols, with n-octanoic acid and n-hexadecanol as the major fatty acid and alcohol, respectively. Preen oils of black-headed gull had higher content of trimethyl fatty acids, 2,8-dimethylundecanoic acid, 2,6-dimethylundecanoic acid and 2,6-dimethylnonanoic acid, and lower content of 2-methyl fatty acids than oils of herring gull and common gull. Preen oils produced by black-headed gull also had lower content of 2-methyl alcohols. The relative contents of n-octanoic acid and n-hexadecanol did not differ among species. The differences among species are probably not a result of different diet, as all gulls fed mainly on household refuse. Hence, preen oil analysis confirmed the taxonomic relations among these gull species, that recently were placed into two different genera.     

Indexing winter gull numbers in Great Britain using data from the 1953 to 2004 Winter Gull Roost Surveys

Capsule Winter Gull Roost Survey data spanning 50 years were used to generate population indices.

Aims To evaluate how wintering numbers of five gull species have changed in Great Britain over the last five decades.

Methods Generalized linear models were used to relate gull numbers to habitat, site and year factors, and so derive species‐specific indices for nine regions of Great Britain. Regional models considered data from different timescales depending on coverage.

Results Patterns of change varied by species and region. All species showed increases in number over the period 1953 to 2004. In most regions, Black‐headed Gull Chroicocephalus ridibundus numbers have declined since peaks between 1973 and 1993; Common Gulls Larus canus have also declined recently in some regions. Lesser Black‐backed Gull L. fuscus numbers have increased dramatically since 1953, whereas numbers of Herring Gull L. argentatus showed large declines between 1963 and 1983. Great Black‐backed Gull L. marinus numbers have increased in the west and the Midlands, but recently declined in eastern regions.

Conclusions Numbers of wintering gulls in Great Britain have shown rapid changes over the last five decades, reflecting changes in the sizes of breeding populations. These changes are likely to be associated with changes in human activities and resource availability.     

A preliminary study on the effects of oyster culturing structures on birds in a sheltered Irish estuary

This study investigated the species composition, numbers and behaviour of birds in an intertidal oyster culture area in Cork Harbour . These data were compared to a nearby area free of aquaculture within the same estuary in March 1999. Species which occurred in the aquaculture free area were also observed in the trestle-area. The most abundant species were oystercatcher Haematopus ostralegus, redshank Tringa totanus, dunlin Calidris alpina, curlew Numenius arquata, black-headed gull Larus ridibundus and common gull Larus canus. Oystercatcher, curlew, black-headed gull and common gull occurred in significantly lower numbers in the trestle area, while for redshank and dunlin the differences were not significant. The percentage of birds feeding did not differ between the two areas. Oystercatcher, redshank, dunlin and curlew mostly fed in both areas. In contrast, black-headed gull and common gull generally did not feed, but surveyed the area. Whether the trestles were covered by oyster bags or not did not have any effect on the number of birds except for the dunlin. Dunlin were significantly more frequent beneath the trestles with bags compared with those without bags. In general, the percentage of birds feeding did not differ between areas. Interspecies differences occurred with regard to the position occupied by birds at the trestles. Oystercatcher, redshank and curlew spent more time underneath the trestles. Dunlin, black-headed gulls and common gulls did not differ in numbers underneath or on top of the trestles. These preliminary observations at a single time period give some insight as to the potential interactions between shellfish aquaculture and intertidal birds.     

Foraging success, kleptoparasitism and feeding techniques in scavenging seabirds: does crime pay?

Scavenging seabirds in the North Sea exploit discards with different success and by different feeding techniques. Northern gannet (Sula bassana) had the highest foraging success index, followed by lesser black-backed gull (Larus fuscus) and black-legged kittiwake (Rissa tridactyla). Northern fulmar (Fulmarus glacialis), mew gull (Larus canus) and black-headed gull (Larus ridibundus) were the least successful species. Ranking species according to the ratio of fish stolen from vs. lost to other species (=robbery index), northern gannet, great black-backed gull (Larus marinus) and great skua (Catharacta skua) were at the top, northern fulmar and black-legged kittiwake at the bottom. Varying compositions of the feeding flocks influenced the foraging success of the species significantly. Both body length and body mass of the birds can well explain species order in the robbery index but not in the foraging success index. Our hypothesis that the most successful species employ particular feeding techniques and/or exhibit the strongest kleptoparasitic abilities could be confirmed to a large extent but not totally. During reduced overall feeding rates, some less successful species and/or species with weaker kleptoparasitic capabilities fared better than during intense feeding rates as predicted, some others did not.     

Expansion of the Mediterranean Gull Larus melanocephalus in Poland

Since 1981, when the first breeding pair of Mediterranean Gull Larus melanocephalus was recorded in Poland, the population of this gull has increased considerably. Its population size was stable until 1997, not exceeding ten pairs annually; thereafter, an increasing number of sightings were made, and during the last 5 years between 26 and 39 breeding pairs have been recorded in Poland. To date, breeding sites have been established in a total of 45 sites (maximum of 19 sites in a given year), with 27% of these (43% of all broods) found on islands located in the middle course of the Vistula River. Breeding sites have also included artificial reservoirs, such as dam reservoirs (20% of sites, 19% of broods), gravel pits (9% of sites, 13% of broods) and fishponds (24% of places, 8% of broods). Mediterranean Gulls were found to nest only within the colonies of other Laridae. Single pairs were recorded at 40% of the breeding sites, whereas a maximum of two to five pairs were recorded at 47% of the other sites. The great majority of breeding attempts were recorded in Black-headed Gull L. ridibundus colonies. In two cases, Mediterranean Gulls bred within mono-specific colonies of Common Gulls L. canus consisting of 60–150 pairs. The biggest concentrations of breeding sites were along the middle course of the Vistula river and in the southern part of Poland.     

Are invasive marsh frogs (Pelophylax ridibundus) replacing the native P. lessonae/P. esculentus hybridogenetic complex in Western Europe? Genetic evidence from a field study

The water-frog L–E system, widespread in Western Europe, comprises the pool frog Pelophylax lessonae and the hybridogenetic edible frog P. esculentus, which originated from hybridization between pool frogs and marsh frogs (P. ridibundus). In P. esculentus, the lessonae (L) genome is eliminated during meiosis and has to be gained anew each generation from a P. lessonae partner, while the ridibundus (R′) genome is transmitted clonally. It therefore accumulates deleterious mutations, so that R′R′ offspring from P. esculentus×P. esculentus crosses are normally unviable. This system is now threatened by invasive P. ridibundus (RR) imported from Eastern Europe and the Balkans. We investigated the genetic interactions between invasive marsh frogs and native water frogs in a Swiss wetland area, and used genetic data collected in the field to validate several components of a recently postulated mechanism of species replacement. We identified neo-ridibundus individuals derived from crosses between invasive ridibundus and native esculentus, as well as newly arisen hybridogenetic esculentus lineages stemming from crosses between invasive ridibundus (RR) and native lessonae (LL). As their ridibundus genomes are likely to carry less deleterious mutations, such lineages are expected to produce viable ridibundus offspring, contributing to species replacement. However, such crosses with invasive ridibundus only occurred at a limited scale; moreover, RR×LL crosses did not induce any introgression from the ridibundus to the lessonae genome. We did not find any ridibundus stemming from crosses between ancient esculentus lineages. Despite several decades of presence on the site, introduced ridibundus individuals only represent 15 % of sampled frogs, and their spatial distribution seems shaped by specific ecological requirements rather than history of colonization. We therefore expect the three taxa to coexist stably in this area.     

Gulls and plovers: host vigilance,kleptoparasite success and a model of kleptoparasite detection

Much interest has focused on the conflict between feeding and vigilance. However, because predator attacks are rarely observed, the adaptive value of time spent vigilant (or non-vigilant through feeding) is difficult to ascertain. On the assumption that the tactics used by plovers (lapwings, Vanellus vanellus and golden plover, Pluvialis apricaria) to avoid attack by kleptoparasitic black-headed gulls (Larus ridibundus) and predators are similar, we develop a model predicting the probability of a gull being detected over any distance. The assumptions of the model are that (a) plovers are attacked whilst nonvigilant (crouching and handling prey) and (b) attacks lasting longer than the target plover's non-vigilant period will be detected. Over many distances there was a fairly close match between the observed and expected risk of the gull being detected. The match was better when the model assumed gulls waited 1 s prior to attacking plovers with large profitable worms. The risks of kleptoparasitism and predation are compared and the adaptive value of the close match between observed and expected curves is discussed.     

Post-maturation treatment improves and synchronizes somatic embryo germination of three species of Japanese pines

Somatic embryos of three Japanese pines, Pinus thunberghii, P. densiflora, and P. armandii var. amamiana, were subjected to different post-maturation treatments to improve both germination and plant conversion frequencies. Slow desiccation of somatic embryos at high relative humidity resulted not only in a marked increment in germination frequencies but also subsequently improved plant conversion rates in all genotypes of the three species tested. Overall three species, germination and plant conversion frequency of somatic embryos was improved by more than fourfold (19?C81%) and more than fivefold (15?C77%), respectively, compared to those of untreated control. In addition, this treatment resulted in a considerable improvement of synchronization of the germination period. The time required for root emergence was synchronized over a half period (28?C14?days) compared with the control. Somatic plants were acclimatized and their growth was monitored in the field.     

Incubation temperature critical to successful stimulation of in vitro zygotic embryo growth in four Australian native Cyperaceae species

Many species of Western Australian Cyperaceae (sedges) are vital components of the indigenous flora but commonly display low seed set, poor seed quality and intractable seed dormancy. We report the effects of incubation temperature and in vitro growth media on whole seed germination compared with extracted zygotic embryo growth in Tetraria capillaris, T. octandra, Lepidosperma drummondii and L. tenue. No germination was observed from intact whole seeds of all test species regardless of the treatment evaluated. In contrast, excised zygotic embryos of all study species exhibited significant increases in growth when cultured at 15°C compared to embryos incubated at 25°C; however, optimal media for embryo growth were genera specific. Extracted embryos of T. capillaris and T. octandra exhibited maximum percentage growth (30 and 40%, respectively) at 15°C on ½ MS medium with no plant growth regulators required. In the case of L. drummondii and L. tenue 1 μM thidiazuron was a necessary addition to the ½ MS medium resulting in 40 and 77% growth of embryos (at 15°C), respectively. Incubation of extracted embryos at 25°C (regardless of medium treatment) resulted in <10% embryo growth for T. octandra and L. tenue, while the remaining two species (L. drummondii, T. capillaris) showed no embryo growth at 25°C on any medium treatment.     

Colonial breeding reduces nest predation in the common gull (Larus canus)

It is often suggested that colonial breeding reduces nest predation for birds with a high defence capacity, but experimental comparison of predation at solitary and colonial nests is seldom feasible within a single species. We here report on such a test in the common gull (Larus canus). The rate of predation on experimental eggs was significantly lower near colonies than near solitary gull nests, and the eggs survived longer at the edge of a colony than farther away. Communal mobbing of nest predators is the likely reason. In both of two years, almost all nests of solitary gulls were destroyed by predators, while most clutches survived in colonies. Nest predation hence selects strongly for colonial breeding in the present population of common gulls.     

Triploidy Induction in the Pacific White Shrimp Litopenaeus vannamei: An Assessment of Induction Agents and Parameters, Embryo Viability, and Early Larval Survival

In this study, we trialed 6-dimethylaminopurine (6-DMAP) chemical shocks to induce meiosis I or meiosis II Pacific White shrimp, Litopenaeus vannamei, triploids for the first time, and cold temperature shocks to induce meiosis II L. vannamei triploids as done previously. Inductions were performed on 37 spawnings in total with experiments being progressively designed in a factorial manner to allow optimization of induction parameters. Treatment with a 200-μm 6-DMAP final concentration at 1?min post-spawning detection for a 6 to 8?min duration resulted in the most consistent induction of chemically induced meiosis I triploids while treatment at 7?min 30?s post-spawning detection for a 10-min duration resulted in the most consistent induction of chemically induced meiosis II triploids. A cold temperature shock of 11.7°C to 13.25°C (final treatment temperature; spawning water temperature 28.5°C) applied at 8?min post-spawning detection for a 4 to 10?min duration resulted in the most consistent induction of cold-temperature-induced meiosis II triploids. 6-DMAP shocks resulted in meiosis I induction rates from 29% to 100% in unhatched embryos and 50% in nauplii, and meiosis II induction rates from 65% to 100% in unhatched embryos and 52% to 100% in nauplii. Cold shocks resulted in induction rates from 5% to 100% in unhatched embryos and nauplii. Confocal microscopy analysis of embryos revealed that there are major developmental abnormalities in a large proportion of later stage triploid L. vannamei embryos compared to their diploid sibling controls. Despite this, however, some triploid embryos did appear normal and both shock agents induced small numbers of viable triploid L. vannamei nauplii which were successfully reared to protozoeal stage 3 as confirmed by flow cytometry. Triploids beyond this life-history stage were not observed in the present study as confirmed by flow cytometry at mysis stages. This study adds to our knowledge base of triploid induction in L. vannamei and further highlights the inherent difficulties with triploid embryonic and larval viability in this species.     

An invasive gull displaces native waterbirds to breeding habitats more exposed to native predators

The effect of invasive opportunistic predators may include population changes in both native prey and native predators as well as alteration of predator–prey interactions. We analyzed the activity of native magpie Pica pica and changes in population, nest sites and nesting success probability of native waterbirds (namely: grebes, ducks, rails and native gulls) in response to the population growth of the invasive Caspian gull Larus cachinnans. The study was carried out at a reservoir in southern Poland and at a similar control reservoir where the Caspian gull was absent. Both the invasive gulls and the native magpie are opportunistic predators of nests of native waterbirds. The population increase of the invasive gull led to a decline in the population of native black-headed gulls Larus ridibundus only. However, the invasive gull displaced all the native species from the breeding islets located in the central part of the reservoir to islets located close to the shoreline. The latter were frequently visited by magpies, which depredated on nests along the shores, leading to an up to threefold decrease in nesting success as compared with nests located in the central area of the invaded reservoir. Predation by Caspian gulls was rarely observed. Thus, the invasion of Caspian gull caused complex direct and indirect effects on the waterbird community that included competition for breeding sites, changes in the spatial distribution of nests and alteration of predation rate by native predators. Moreover, the effects of invasion may not be reflected by changes in population size of native species.     

Predation by gulls on crabs in rocky intertidal and shallow subtidal zones of the Gulf of Maine

Most organisms in intertidal areas are marine in origin; many have distributions that extend into the subtidal zone. Terrestrial predators such as mammals and birds may exploit these animals during low tide and can have considerable effects on intertidal food webs. Several studies have shown that avian predators are capable of reducing densities of sessile and slow-moving intertidal invertebrates but very few studies have considered avian predation on mobile invertebrate predators such as crabs. In this study, we investigated predation by Great Black-backed Gulls (Larus marinus Linnaeus) on three species of crabs (Cancer borealis Stimpson, Cancer irroratus Say, and Carcinus maenas Linnaeus). The study was at Appledore Island, ME (a gull breeding island) and 8 other sites throughout the Gulf of Maine, including breeding islands and mainland sites. On Appledore Island, intertidal and subtidal zones provided over one-third of prey remains found at gull nests, and crabs were a substantial proportion (∼ 30% to 40%) of the total remains. Similarly, collections of prey remains from intertidal areas indicated that crabs were by far the most common marine prey. C. borealis was eaten far more often and C. irroratus and C. maenas less often than expected at each site. Comparing numbers of carapaces to densities of crabs in low intertidal and shallow subtidal zones at each site, we estimated that gulls remove between 15% and 64% of C. borealis during diurnal low tides. The proportion of C. borealis eaten by gulls was independent of proximity to a gull colony. Approximately 97% of the outer coast of Maine is within 20 km of a breeding island. Thus, a lot of gull predation on crabs may occur throughout the Gulf of Maine during summer months. Crabs are important predators of other invertebrates; if predation by gulls reduces the number of crabs in intertidal and shallow subtidal areas, gulls may have important indirect effects on intertidal food webs.     

Occurrence ofCandida albicans in fresh gull feces in temperate and subtropical areas

The occurrence ofCandida albicans in fresh gull (Larus spp.) feces was compared in temperate and subtropical locations. Of 239 fresh samples, 133 were obtained in southeastern Connecticut and 106 from different sites on the southeastern and central western coasts of Florida. Overall, 60% of all feces containedC. albicans. Of the Connecticut samples, 78% were positive, whereas 38% of the Florida samples revealed the presence of the yeast. Only 1 of 24 samples of fresh brown pelican feces containedC. albicans. Differences inC. albicans occurrence in birds in various locations was ascribed to variations in habitat and feeding behavior. Samples of water from a municipal reservoir in Connecticut were routinely positive, with an average cell density of 20/liter. Two fresh gull samples obtained on the reservoir bank containedC. albicans at an average cell concentration of 5, 200/g. The frequency ofC. albicans in gull droppings was higher than reported by others, and the yeast is common in temperate waters. These findings have important public health implications.     

Analysis of the Gull Fecal Microbial Community Reveals the Dominance of Catellicoccus marimammalium in Relation to Culturable Enterococci

Gulls are prevalent in beach environments and can be a major source of fecal contamination. Gulls have been shown to harbor a high abundance of fecal indicator bacteria (FIB), such as Escherichia coli and enterococci, which can be readily detected as part of routine beach monitoring. Despite the ubiquitous presence of gull fecal material in beach environments, the associated microbial community is relatively poorly characterized. We generated comprehensive microbial community profiles of gull fecal samples using Roche 454 and Illumina MiSeq platforms to investigate the composition and variability of the gull fecal microbial community and to measure the proportion of FIB. Enterococcaceae and Enterobacteriaceae were the two most abundant families in our gull samples. Sequence comparisons between short-read data and nearly full-length 16S rRNA gene clones generated from the same samples revealed Catellicoccus marimammalium as the most numerous taxon among all samples. The identification of bacteria from gull fecal pellets cultured on membrane-Enterococcus indoxyl-β-d-glucoside (mEI) plates showed that the dominant sequences recovered in our sequence libraries did not represent organisms culturable on mEI. Based on 16S rRNA gene sequencing of gull fecal isolates cultured on mEI plates, 98.8% were identified as Enterococcus spp., 1.2% were identified as Streptococcus spp., and none were identified as C. marimammalium. Illumina deep sequencing indicated that gull fecal samples harbor significantly higher proportions of C. marimammalium 16S rRNA gene sequences (>50-fold) relative to typical mEI culturable Enterococcus spp. C. marimammalium therefore can be confidently utilized as a genetic marker to identify gull fecal pollution in the beach environment.     

Estimating the contribution of carnivorous waterbirds to nutrient loading in freshwater habitats

1. We estimated nitrogen (N) and phosphorus (P) loading into wetlands by carnivorous waterbirds with alternative physiological models using a food‐intake and an excreta‐production approach. The models were applied for non‐breeding and breeding Dutch inland carnivorous waterbird populations to quantify their contribution to nutrient loading on a landscape scale. 2. Model predictions based on food intake exceeded those based on excretion by 59–62% for N and by 2–36% for P, depending on dietary assumptions. Uncertainty analysis indicated that the intake model was most affected by errors in energy requirement, while the excretion model was dependent on faecal nutrient composition. 3. Per capita loading rate of non‐breeders increased with body mass from 0.3–0.8 g N day^?1 and 0.15 g P day^?1 in little gulls Larus minutus to 4.5–11.5 g N day^?1 and 2.1–3.2 g P day^?1 in great cormorants Phalacrocorax carbo. For breeding birds, the estimated nutrient loading by a family unit over the entire breeding period ranged between 17.6–443.0 g N and 8.6 g P for little tern Sterna albifrons to 619.6–1755.6 g N and 316.2–498.1 g P for great cormorants. 4. We distinguished between external (i.e. importing) and internal (i.e. recycling) nutrient loading by carnivorous waterbirds. For the Netherlands, average external‐loading estimates ranged between 38.1–91.5 tonnes N and 16.7–18.2 tonnes P per year, whilst internal‐loading estimates ranged between 53.1–140.5 tonnes N and 25.2–39.2 tonnes P and per year. The average contribution of breeding birds was estimated to be 17% and 32% for external and internal loading respectively. Most important species were black‐headed gull Larus ridibundus and mew gull Larus canus for external loading, and great cormorant and grey heron Ardea cinerea for internal loading. 5. On a landscape scale, loading by carnivorous waterbirds was of minor importance for freshwater habitats in the Netherlands with 0.26–0.65 kg N ha^?1 a^?1 and 0.12–0.16 kg P ha^?1 a^?1. However, on a local scale, breeding colonies may be responsible for significant P loading.     

The Auditory Mechanics of the Outer Ear of the Bush Cricket: A Numerical Approach

Bush crickets have tympanal ears located in the forelegs. Their ears are elaborate, as they have outer-, middle-, and inner-ear components. The outer ear comprises an air-filled tube derived from the respiratory trachea, the acoustic trachea (AT), which transfers sound from the mesothoracic acoustic spiracle to the internal side of the ear drums in the legs. A key feature of the AT is its capacity to reduce the velocity of sound propagation and alter the acoustic driving forces of the tympanum (the ear drum), producing differences in sound pressure and time between the left and right sides, therefore aiding the directional hearing of the animal. It has been demonstrated experimentally that the tracheal sound transmission generates a gain of ∼15 dB and a propagation velocity of 255 ms⁻¹, an approximately 25% reduction from free-field propagation. However, the mechanism responsible for this change in sound pressure level and velocity remains elusive. In this study, we investigate the mechanical processes behind the sound pressure gain in the AT by numerically modeling the tracheal acoustic behavior using the finite-element method and real three-dimensional geometries of the tracheae of the bush cricket Copiphora gorgonensis. Taking into account the thermoviscous acoustic-shell interaction on the propagation of sound, we analyze the effects of the horn-shaped domain, material properties of the tracheal wall, and the thermal processes on the change in sound pressure level in the AT. Through the numerical results obtained, it is discerned that the tracheal geometry is the main factor contributing to the observed pressure gain.     

Volume contents volume 38 (1985)

Isolated microspores from six cultivars of Brassica napus and one of B. carinata were cultured in modified Nitsch and Nitsch (NN) medium supplemented with 13% (W/V) sucrose, 0.05 mg/l benzyladenine (BA) and 1.00 mg/l nahpthaleneacetic acid (NAA). Embryogenic responses were observed at cultured temperatures ranging from 22 to 32°C. For most genotypes tested, the highest frequency of embryos occurred at 30°C and 7–54 embryos per anther (approx. 17 000 microspores per anther) developed. Although incubation at 30°C produced the highest frequency of embryos, lower culture temperatures induced better quality embryos. A split temperature culture regime of incubation at 32°C for 3 days followed by incubation at 25°C resulted in both high embryo yields and a high percentage of normal embryos. Plantlet development from microspore-derived embryos appeared to be influenced by both genotype and medium.     

In situ Development of Perch Eggs,Perca fluviutilis L. (Pisces,Percidae) in a Small Eutrophic Lake,Lake Plussee,Holstein, Germany

Naturally spawned egg strands of perch, Perca fluviatilis L. were sampled from exposed fir trees submerged in Lake Plußsee, Holstein, Northern Germany from April to May 1989. These were incubated in situ and in the laboratory to estimate the viability, development and abnormalities of the embryos. From the in siru incubated eggs 91.6% embryos were viable, the nonviable portion comprising 1.1 % unfertilized eggs, 5.1 % dead and 2.2 % with abnormalities. As compared to the eggs incubated in the laboratory with 84.1 % viable embryos, the nonviable portion consisting 1.1 % unfertilized eggs, 11.3 % dead and 3.5 % with abnormalities. Incubation rate of P. fluviatilis embryos both in situ and laboratory, ranged from 200-210 ATUs (10°C in situ and 8°C in the laboratory) with incubation period of 20-27 days from fertilization to 50 % hatching.     

The relationship between plankton-feeding Bonaparte's and Mew Gulls and tidal upwelling at Active Pass, British Columbia

The food habits of Bonaparte's (Larus Philadelphia) and MewGulls (L. canus) were studied at Active Pass, British Columbia,in relation to upwelling of zooplankton. Bonaparte's Gulls fedmostly on planktonic crustaceans during September-November andagain during April-May, while Mew Gulls foraged there chieflyin February and March. Both species ate predominantly the euphausiid,Thysanoessa raschii, in spring, while Bonaparte's Gulls fedmainly on the amphipods, Parathemisto pacifica and Calliopiuslaeviusculus, in fall. Year-round sampling of zooplankton andcollection of temperature and salinity data showed gull numbersto correlate with times of maximum upwelling and abundance ofzooplankton prey in surface waters. Outside the upwelling zonein Active Pass, Bonaparte's and Mew Gulls fed mostly on fishesand intertidal organisms, but also on zooplankton along tidelines.