Fish fed to young Guillemots, Uria aalge, and used in display on the Isle of May, Scotland

Guillemots on the Isle of May fed their young on Sandeels and Sprats, the proportion of the latter being highest late in the day and the season. There was a peak of feeding after dawn when many large Sandeels were brought. Weather had no effect on feeding rate but this did increase with the chicks age. Food appeared to be abundant. A large Sprat was the most efficient return for effort and Guillemots may select the most energy-rich prey. Display fish (mainly small Sandeels) were brought throughout the season, mostly by females which often ate them later. The significance of the fish-carrying display is obscure.     

The basis of food selection in some estuarine fishes. Eels, Anguilla anguilla (L.), whiting, Merlangius merlangus (L.), sprat, Sprattus sprattus (L.) and stickleback, Gasterosteus aculeatus L.

The factors influencing the selection of food by eels, Anguilla anguilla, whiting, Merlanglus merlangius, sprat, Sprattus sprattus, and stickleback, Gasterosteus aculeatus have been investigated by analysing collections made in the Severn Estuary for 1 year. Non–migratory (yellow) eels measuring from 19–5–56–5 cm in length fed mainly on either the decapod Crangon vulgaris or on the mysid Neomysis integer during the warmer months but ceased to feed in the winter. Whiting measuring between 2–5 and 15 cm fed almost exclusively on C. vulgaris, N. integer and the sand goby, Pomatoschistus minutus. Sprats fed chiefly on either the arnphipod Gammarus salinus or N. integer. Sticklebacks seldom contained any food in their stomachs despite the presence of large quantities of suitable prey and the high level of hunting efficiency. Gammarus salinus, although normally abundant in the environment, was usually ingested in disproportionately small quantities by all fishes except sprats reflecting its concealment among floating weeds and a selection against small (less than 1 cm) organisms. Because of the limitations of size and the unusually efficient escape reaction of larger animals, only young representatives of Crangon vulgaris were captured. The isopod Eurydice pulchra was rarely eaten by any of the fishes even though it was common in the environment. Burrowing polychaetes, mainly Nereis diversicolor, were never utilized possibly due to the difficulty involved in removing these organisms from the substrate. Neomysis integer was the most frequently consumed organism. Although the average length of prey ingested by the whitings increased with the size of fish, this was not the case for the other species. The proportion of non–feeding eels and the dry weight of stomach contents of this species depended on the temperature of the water but were not related to the availability of prey and tidal conditions whereas the feeding of whiting could not be related to any environmental parameter.     

Diet segregation between two colonies of little penguins Eudyptula minor in southeast Australia

We studied foraging segregation between two different sized colonies of little penguins Eudyptula minor with overlapping foraging areas in pre‐laying and incubation. We used stomach contents and stable isotope measurements of nitrogen (δ¹⁵N) and carbon (δ¹³C) in blood to examine differences in trophic position, prey‐size and nutritional values between the two colonies. Diet of little penguins at St Kilda (small colony) relied heavily on anchovy while at Phillip Island (large colony), the diet was more diverse and anchovies were larger than those consumed by St Kilda penguins. Higher δ¹⁵N values at St Kilda, differences in δ¹³C values and the prey composition provided further evidence of diet segregation between colonies. Penguins from each colony took anchovies from different cohorts and probably different stocks, although these sites are only 70 km apart. Differences in diet were not reflected in protein levels in the blood of penguins, suggesting that variation in prey between colonies was not related to differences in nutritional value of the diet. Anchovy is currently the only available prey to penguins throughout the year and its absence could have a negative impact on penguin food supply, particularly at St Kilda where the diet is dominated by this species. While it is difficult to establish whether diet segregation is caused by inter‐ or intra‐colony competition or spatial differences in foraging areas, we have shown that colonies with broadly overlapping foraging ranges could have significant differences in trophic position, diet composition and prey size while maintaining a diet of similar nutritional value.     

The winter diet of the Atlantic Puffin Fratercula arctica around the Faroe Islands

Most mortality of Atlantic Puffins occurs outside the breeding season but little is known about the species’ diet at that time. The stomach contents of 176 Puffins shot legally for food around the Faroe Islands between October and January in three winters were examined. The remains of 20 species of fish, six species of crustacea and single species of polychaete, chaetognathid and squid were identified. The most frequently recorded prey in terms of frequency of occurrence were 0 group (< 1 year old) Lesser Sandeel Ammodytes marinus (82% of stomachs), followed by mesopelagic fish (52%), nereid worms (41%), Silver Rockling Gaidropsarus argentatus (36%), crustacea (35%), large sandeel (32%) and other large fish (32%). In terms of calculated biomass, nereids (41%), large sandeel (23%) and other large fish (17%) made up the bulk of the diet but the latter two prey types were most important in energetic terms (46% despite accounting for only 9% of items). Stomach contents collected on the same day and location were significantly more similar than those collected on different dates and locations, suggesting that during the winter, Puffins are generalists, taking any prey they encounter.     

BREEDING PERFORMANCE OF PUFFINS FRATERCULA ARCTICA IN RELATION TO NEST DENSITY, LAYING DATE AND YEAR

The paper presents data on the breeding and predation of Puffins in two areas of different nest density within a single colony on Dun, St Kilda group, Outer Hebrides in 1973-78.
Within a season birds laying early had a slightly higher nesting success than birds laying late, but laying date had little influence on the peak and fledging weights of young. The main disadvantage in late laying was a reduced chance of relaying if the first egg was lost.
Breeding success and chick weights varied from year to year. The 1974 season was the least successful with the lowest nesting success, lowest frequency of feeds, lowest calorific value of feeds, lightest chicks and slowest growth. Overall breeding performance was not related to the annual mean laying dates.
In all years pairs nesting in the area of high nest density did better than pairs nesting at low density. The effect is attributed to differential predation and disturbance by predatory gulls. At least 4.2% of adult Puffins breeding in the area of low burrow density were killed by gulls each breeding season; this is higher than the total annual mortality found in three other studies. Only 0.9% of adults from the high density area were found killed. The subpopulation in the low density area cannot survive without much immigration, yet there is no evidence that this happens.     

The visual fields of Common Guillemots Uria aalge and Atlantic Puffins Fratercula arctica: foraging,vigilance and collision vulnerability

Significant differences in avian visual fields are found between closely related species that differ in their foraging technique. We report marked differences in the visual fields of two auk species. In air, Common Guillemots Uria aalge have relatively narrow binocular fields typical of those found in non‐passerine predatory birds. Atlantic Puffins Fratercula arctica have much broader binocular fields similar to those that have hitherto been recorded in passerines and in a penguin. In water, visual fields narrow considerably and binocularity in the direction of the bill is probably abolished in both auk species. Although perceptual challenges associated with foraging are similar in both species during the breeding season, when they are piscivorous, Puffins (but not Guillemots) face more exacting perceptual challenges when foraging at other times, when they take a high proportion of small invertebrate prey. Capturing this prey probably requires more accurate, visually guided bill placement and we argue that this is met by the Puffin's broader binocular field, which is retained upon immersion; its upward orientation may enable prey to be seen in silhouette. These visual field configurations have potentially important consequences that render these birds vulnerable to collision with human artefacts underwater, but not in air. They also have consequences for vigilance behaviour.     

Unravelling dispersal patterns in an expanding population of a highly mobile seabird,the northern fulmar (Fulmarus glacialis)

The northern fulmar (Fulmarus glacialis) is an abundant seabird whose Northeast Atlantic population has expanded dramatically over the past 100 years. Archaeological evidence suggests that Iceland and St Kilda were the ancestral populations from which essentially all other colonies in the region were derived. We collected samples from seven breeding colonies around the North Atlantic and used mitochondrial DNA analysis to ask whether population structure was present and, if so, where there was evidence about which colony was the dominant source population. Our data reveal a pattern consistent with isolation by distance, suggesting that, even though capable of flying great distances, most birds return to breed either at their own or neighbouring colonies. Interestingly, although most colonizers appear to have come originally from Iceland, our analysis also identifies St Kilda as a possible source. However, this secondary pattern appears to be largely an artefact, and can be attributed to the low haplotype diversity on St Kilda which yields a much clearer isolation by distance signal than that generated by birds dispersing from Iceland, where haplotype diversity is extremely high. Consequently, we urge caution when interpreting patterns in which populations vary greatly in the genetic diversity they harbour.     

4. SOME BIRDS OBSERVED AT LAKE MENTZ

Randall, R. M. &; Randall, B. M. 1900. The hard-shell4 diet of African Black Oystercatcher chicks at St Croix Island, South Africa. Ostrich 53:157-163.

The hard-shelled diet of African Black Oystercatcher Haematopus moquini chicks was established by monitoring piles of food remains brought to the chicks. Mussels were the dominant prey species constituting about 90% numerically and about 95% by mass. Limpets were the next most abundant prey item, while false limpets, keyhole limpets and whelks were present in small numbers. Transects down the intertidal area showed that African Black Oystercatchers ignored some abundant species such as barnacles and small gastropods. They took most prey species in the same relative proportion that they were represented in transects, but there was evidence of selection for limpets and avoidance of false limpets and whelks. The modal size class of mussels in feeding piles was greater than in transects.     

Prey choice by marten during a decline in prey abundance

Summary We examined variation in diet choice by marten (Martes americana) among seasons and between sexes and ages from 1980–1985. During this period prey populations crashed simultaneously, except for ruffed grouse (Bonasa umbellus) which was common at the beginning and end of the study, and masked shrews (Sorex cinereus) which were abundant in 1983. Marten were catholic in selection of prey and made use of most available mammalian prey, ruffed grouse, passerine birds, berries, and insects. Diet niche was widest during the latter three years when prey was scare, particularly in late winter. Diet niche breadth was negatively correlated with abundance of all common prey species. Proportion of small prey species in the diet was correlated with absolute abundance of those species, but proportion of some large prey was related to their relative abundance. Diet choice varied among years and among seasons. Berries and insects were common in summer diets while large prey, particularly varying hare (Lepus americanus), were more frequent in winter diet than in summer diet. We found little evidence that any small mammal species was a preferred prey. Sexual size dimorphism between the sexes did not affect prey choice, nor did age. Reduced foraging effort in winter resulted in a wider diet niche only when prey was scarce. The only prediction of optimal foraging models fully supported by our data was a wider diet niche with reduced prey abundance. However, among the three most profitable prey species choice was dependent on the absolute abundance of the most profitable type (varying hare). We suggest that marten primarily forage for large prey but employ a strategy which results in encounters with small prey as well. These small prey are eaten as they provide energy at minimal cost, between captures of large prey.     

Diets and feeding of Fulmars Fulmarus glacialis during the breeding season:a comparison between St Kilda and Shetland colonies

Diets and nest attendance of Fulmars at Foula, Shetland and St Kilda, Outer Hebrides were examined during the breeding season. At Foula, sandeels formed the bulk of the diet, with fish offal and pelagic zooplankton of minor importance. At St Kilda, 71% of regurgitates consisted of pelagic zooplankton, probably captured at night. Dietary overlap between the two colonies was 14% by species composition. Foraging trips from Foula shortly after chick hatching generally lasted for less than 10 h, while trips from St Kilda late in chick rearing often lasted more than 24 h. The diurnal pattern of feeding suggested mainly nocturnal foraging from St Kilda but both diurnal and nocturnal foraging from Foula.     

Prey selectivity affects reproductive success of a corallivorous reef fish

Most animals consume a narrower range of food resources than is potentially available in the environment, but the underlying basis for these preferences is often poorly understood. Foraging theory predicts that prey selection should represent a trade-off between prey preferences based on nutritional value and prey availability. That is, species should consume preferred prey when available, but select less preferred prey when preferred prey is rare. We employed both field observation and laboratory experiments to examine the relationship between prey selection and preferences in the obligate coral-feeding filefish, Oxymonacanthus longirostris. To determine the drivers of prey selection, we experimentally established prey preferences in choice arenas and tested the consequences of prey preferences for key fitness-related parameters. Field studies showed that individuals fed almost exclusively on live corals from the genus Acropora. While diet was dominated by the most abundant species, Acropora nobilis, fish appeared to preferentially select rarer acroporids, such as A. millepora and A. hyacinthus. Prey choice experiments confirmed strong preferences for these corals, suggesting that field consumption is constrained by availability. In a longer-term feeding experiment, reproductive pairs fed on non-preferred corals exhibited dramatic reductions to body weight, and in hepatic and gonad condition, compared with those fed preferred corals. The majority of pairs fed preferred corals spawned frequently, while no spawning was observed for any pairs fed a non-preferred species of coral. These experiments suggest that fish distinguish between available corals based on their intrinsic value as prey, that reproductive success is dependent on the presence of particular coral species, and that differential loss of preferred corals could have serious consequences for the population success of these dietary specialists.     

Sex-specific differences in body condition indices and seasonal mass loss in Tufted Puffins

ABSTRACT.   Reduced prey availability can affect the growth and survival of nestling seabirds. However, few studies have demonstrated similar effects on indices of adult body condition. We examined body condition and seasonal mass loss of breeding adult male and female Tufted Puffins ( Fratercula cirrhata ) at Chiniak Bay, Kodiak Island, Alaska, in 2004–2005. We determined sex using genetic analysis, developed a discriminant function to determine sex using morphometric measurements, and examined the body condition of adult males and females relative to the growth rates of their offspring. We found that morphological measurements were only moderately useful for sexing Tufted Puffins, with 74% of adults ( N = 176) correctly classified. We also found that the relationship between adult body mass and size differed between sexes and conclude that body condition indices must be calculated separately for each sex to avoid inter- and intrasexual bias. Body condition of male and female Tufted Puffins declined during the chick-rearing period. However, body condition of females did not differ between years, whereas male condition declined to a greater degree during 2004 when the mass of young at fledging was significantly lower. Although these results suggest that adult male Tufted Puffins sacrifice their own body condition in years of diminished nestling growth and females do not, reasons for this apparent intersexual difference in reproductive strategies remain unclear.     

Between-lake differences in the diet and provisioning behaviour of Black-throated Divers Gavia arctica breeding in Scotland

Surveys at 23 Black-throated Diver breeding lakes in Scotland showed large between-lake differences in the species and size range of potential prey. The study lakes were classified into four types according to the main size-taxa prey classes present. Type 1 lakes lacked small fish, Type 4 lacked salmonids < 300 mm and Types 2 and 3 both had all four of the main prey classes. Diver diet for 30 families at the study lakes was quantified from 7943 prey items seen fed to chicks, and 153 items seen eaten by adults, during 662 h of observations. At all lake types adults mostly ate salmonids of 120–240 mm in length, especially Brown Trout Salmo trutta , and European Eels Anguilla anguilla up to c.  350 mm. The prey eaten by chicks ranged widely, from c.  0.03 g to 300 g, with important implications for feeding behaviour. Young chicks (days 1–8) rejected items greater than 70 mm long. The diet of young chicks consisted mostly of small fish, either Three-spined Sticklebacks Gasterosteus aculeatus (Type 2 lakes) or Minnow Phoxinus phoxinus (Type 3 and Type 4 lakes). At other lakes (Type 1) it consisted mostly of mayfly larvae (Ephemeroptera); invertebrates were the only abundant potential small prey in these lakes. At all lakes the chick diet became more similar to that of adults as chicks grew. Adults provisioning chicks used two foraging strategies. In 'excursion foraging', adults hunted away from the chicks and carried prey back for them; in 'attendance foraging', the chicks accompanied the foraging adult(s). Excursion foraging was used mostly before day 4 and was strongly and positively correlated with the abundance of fish < 80 mm in length. This behaviour is probably adaptive, but is probably tenable only where small fish are relatively abundant. Young chicks fed mainly on small fish had higher survival rates than those fed on invertebrates.     

Prey profitability for adult Grey Herons Ardea cinerea and the constraints on prey size when feeding young nestlings

Patterns of handling time and profitability are examined for adult Grey Herons feeding on carp, eels and catfish. Handling times generally increased with prey size but were influenced markedly by the morphology and behaviour of the prey. Profitability was highest for carp (max. 0.9 g/s for 15–20 cm fish), lowest for catfish (max. 0.05 g/s) and intermediate for eels (max. 0.1 g/s). Nestlings were unable to ingest the sizes of fish most profitable for the adults to consume until aged 20 days; by the age of 30 days, they could consume the full size-range of prey taken by the adults. In order to feed their young chicks, adults must therefore either select smaller prey, or break their large prey into smaller pieces. The diet of nestling Grey Herons in the Camargue is examined for evidence to support or refute the former hypothesis.
Young nestlings (≤20 days) regurgitated smaller carp than old nestlings (> 20 days). Comparison of prey types in the diet of the two groups showed that small prey species occurred significantly more often in the diet of young chicks, while the converse was true for larger prey species. The occurrence of particular prey types in the diet only of young chicks suggests that adults may forage in more marginal, shallower water (where small prey are probably more abundant) to meet the requirements of their brood during the early part of the nestling phase. The second hypothesis, that the adults break down large prey into smaller pieces, was not examined, although evidence from other studies suggests that this does occur; both mechanisms may therefore be important.     

Diets and body condition of polar cod (<Emphasis Type="Italic">Boreogadus saida</Emphasis>) in the northern Bering Sea and Chukchi Sea

To understand trophic responses of polar cod Boreogadus saida (a key species in Arctic food webs) to changes in zooplankton and benthic invertebrate communities (prey), we compared its stomach contents and body condition between three regions with different environments: the northern Bering Sea (NB), southern Chukchi Sea (SC), and central Chukchi Sea (CC). Polar cod were sampled using a bottom trawl, and their potential prey species in the environment were sampled using a plankton net and a surface sediment sampler. Polar cod fed mainly on appendicularians in the NB and SC where copepods were the most abundant in the environment, while they fed on copepods, euphausiids, and gammarids in the CC where barnacle larvae were the most abundant species in plankton samples on average. The stomach fullness index of polar cod was higher in the NB and SC than CC, while their body condition index did not differ between these regions. The lower lipid content of appendicularians compared to other prey species is the most plausible explanation for this inconsistency.     

Diet and prey selection of sympatric tropical skinks

Most skinks are opportunistic predators, taking available prey from the environment as it is encountered. Variation in their diet composition is thought to reflect differences in prey abundance in the environment. We studied diet composition and prey selection in a community of three sympatric skink species (genus Carlia) in northern Australia by comparing contents of skink stomachs with arthropod prey available in their habitat. Carlia were entirely carnivorous and fed on a range of arthropod prey. We found high overlap in diet and prey size among the three species and between the wet and dry seasons, but found that skinks generally focused their foraging efforts on prey types and prey sizes that were not abundant in the habitat. Spiders (Aranea), orthopterans, blattarians, isopods and termites (Isoptera) were important prey of skinks, but these arthropods were rarely trapped in the environment. Skinks also frequently consumed large‐bodied prey, despite the higher relative abundance of small prey in the environment. Skinks were more selective in their foraging and diet than previously assumed. Selection of prey by consumers is a fundamental ecological process, important to consumers for maintaining energy requirements to grow and reproduce, but equally important to the community dynamics of the prey consumed.     

PREDATION AND KLEPTOPARASITISM BY SKUAS IN A SHETLAND SEABIRD COLONY

Feeding methods and relations of Great Skuas and Arctic Skuas to prey were studied in a seabird colony at Hermaness, Shetland. Great Skuas obtained food by kleptoparasitism, predation and scavenging. They induced Gannets to regurgitate by interfering with their flight; grasping the Gannet by the wing or tail or pushing it down with the feet on its back. Gannets tried to escape by descending to the surface, and regurgitated during 12% of the chases, most frequently when pursued by several birds. Great Skuas caught Puffins by swooping at flocks in the colony. Puffins flying with fish to their young were also chased, releasing food on one fifth of the attacks, or escaping down to the sea and diving. Great Skuas also took Kittiwake nestlings by hovering and grasping the chick with the bill, killing and eating it on the surface. Adult Kittiwakes from nearby nests took to the air, mobbing the predator. More Kittiwakes were engaged in mobbing at unsuccessful than at successful predation attempts, indicating that colonial breeding may be of selective value under such predation. Two different estimates pointed to a Kittiwake nestling predation of 0–12 and 014 young per pair. Fledging success of Kittiwakes was estimated at 0–87-1-06 young per pair, considerably lower than at English colonies where predators are absent. In spite of the predation, the Kittiwake colony showed no signs of decrease. Agonistic behaviour and other evidence indicate that Great Skuas defend feeding territories at the seabird colony. Skuas, gulls and Fulmars competed for food at carcasses. Fulmars dominated and chased away skuas. Arctic Skuas deprived Puffins of food. They patrolled the cliff, intercepting Puffins arriving with fish, snatching it from their victim's bill, or inducing them to release fish. Puffins continuing their inward flight lost food more often (30%) than birds descending to the sea (15%)—sometimes diving below. This opportunity to escape may explain the lower success of skuas at Hermaness than at a Puffin colony farther inland from the shore (Grant 1971). Other factors being equal, proximity to the sea may thus reduce the risk of kleptoparasitism.     

Foraging behavior of Cerulean Warblers during the breeding and non‐breeding seasons: evidence for the breeding currency hypothesis

Birds require additional resources for raising young, and the breeding currency hypothesis predicts that insectivorous species exploit large soft‐bodied prey during the breeding season, but shift to small, likely hard‐bodied, prey during the non‐breeding season. To test this hypothesis, we examined prey use by Cerulean Warblers (Setophaga cerulea), foliage‐gleaning Nearctic‐Neotropical migrants, during the breeding and non‐breeding seasons. We collected data on foraging behavior during the breeding season (including observations of prey items fed to young) in upland mixed‐oak forest in southeastern Ohio in 2009 and 2010 and, during the non‐breeding season, in shade coffee in the Cordillera de Merida, Venezuela, in 2008–2009. Cerulean Warblers captured 7% more large prey (visible prey extending beyond the bill) during the breeding than the non‐breeding season, but foraged at similar rates during both seasons. Large, soft‐bodied prey appeared to be especially important for feeding young. We found that adults delivered large prey on >50% of provisioning visits to nests and 69% of identifiable large prey fed to nestlings were greenish larvae (likely Lepidoptera or caterpillars) that camouflage against leaves where they would tend to be captured by foliage‐gleaning birds. Availability of specific taxa appeared to influence tree species foraging preferences. As reported by other researchers, we found that Cerulean Warblers selected trees in the genus Carya for foraging and our examination of caterpillar counts from the central Appalachian Mountains (Butler and Strazanac 2000 ) showed that caterpillars with greenish coloration, especially Baileya larvae, may be almost twice as abundant on Carya than Quercus. Our results provide evidence for the breeding currency hypothesis, and highlight the importance of caterpillars to a foliage‐gleaning migrant warbler of conservation concern.     

Diet composition and prey preference of tench, Tinca tinca (L.), common bream, Abramis brama (L.), perch, Perca fluviatilis L. and roach, Rutilus rutilus (L.), in two contrasting gravel pit lakes: potential trophic overlap with wildfowl

The abundance of benthic macroinvertebrate taxa and the relative abundance of zooplankton taxa were compared with the diet of bream, tench. perch and roach from two gravel pit lakes during May-July 1986 and 1987. Significant food preferences were demonstrated between species and between lakes. Chironomid pupae dominated the macroinvertebrate diet of perch, roach, ate predominantly either Spirogyra sp. (St Peters Lake) or Daphniu hyalina (Main Lake).
The Main Lake, bream fed largely upon chironomid larvae and the bivalve Sphuerium but in St Peters Lake they positively selected a variety of less abundant benthic invertebrate taxa. Bream switched from benthos to zooplankton in the Main Lake in 1986. Tench ate large numbers of Aselhs and showed positive selection of various macroinvertebrate prey in St Peters but ate D. hjulim in Main Lake. Tropic overlap for chironomids and other macroinvertebrate prey was demonstrated between perch, bream and tench, and potentially with wildfowl which used the gravel pits for breeding and wintering.     

The feeding success of cattle egrets in flocks

The feeding rates of grouped (<1.5 m from conspecifics) and solo (>5 m from conspecifics) cattle egrets (Bubulcus ibis) in loose flocks away from cows were compared, to test the hypothesis that grouped cattle egrets benefit from feeding on prey flushed inadvertently by nearby conspecifics. The flock feeding rates were also compared to those of grouped and solo egrets near cows, to determine the effects of flock membership on feeding rates. Birds in flocks captured prey faster than those with cows, and tended to capture larger prey, but field observations and captive experiments failed to show that the feeding success of flock members was enhanced by the hypothesized ‘beater’ effect. Increases in prey density, however, always resulted in higher feeding rates, so some cattle egret groups may form in response to local concentrations of prey. Prey size may also play a role in group formation, because birds in the field tended to feed at greater distances from their neighbours when larger prey were captured, regardless of prey density. When small groups did form among cattle egrets feeding on relatively large prey, group members occasionally captured prey items that had been discovered by nearby conspecifics. This behaviour was not observed among birds in dense aggregations, which fed on small, highly abundant prey. These data indicate that there is a potential cost associated with feeding too near others unless the prey are relatively small and abundant.