Benefits of Group Foraging Depend on Prey Type in a Small Marine Predator,the Little Penguin

Group foraging provides predators with advantages in over-powering prey larger than themselves or in aggregating small prey for efficient exploitation. For group-living predatory species, cooperative hunting strategies provide inclusive fitness benefits. However, for colonial-breeding predators, the benefit pay-offs of group foraging are less clear due to the potential for intra-specific competition. We used animal-borne cameras to determine the prey types, hunting strategies, and success of little penguins (Eudyptula minor), a small, colonial breeding air-breathing marine predator that has recently been shown to display extensive at-sea foraging associations with conspecifics. Regardless of prey type, little penguins had a higher probability of associating with conspecifics when hunting prey that were aggregated than when prey were solitary. In addition, success was greater when individuals hunted schooling rather than solitary prey. Surprisingly, however, success on schooling prey was similar or greater when individuals hunted on their own than when with conspecifics. These findings suggest individuals may be trading-off the energetic gains of solitary hunting for an increased probability of detecting prey within a spatially and temporally variable prey field by associating with conspecifics.     

Landscape structure influences the use of social information in an insectivorous bat

In anthropogenic landscapes, aerial insectivores are often confronted with variable habitat complexity, which may influence the distribution of prey. Yet, high mobility may allow aerial insectivores to adjust their foraging strategy to different prey distributions. We investigated whether aerial-hunting common noctules Nyctalus noctula adjust their foraging strategy to landscapes with different habitat complexity and assumingly different prey distribution. We hypothesized that the movement behaviour of hunting common noctules and changes of movement behaviour in reaction towards conspecifics would depend on whether they hunt in a structurally poor cropland dominated landscape or a structurally rich forest dominated landscape. We tracked flight paths of common noctules in northeastern Germany using GPS loggers equipped with an ultrasonic microphone that recorded foraging events and presence of conspecifics. Above cropland, common noctules hunted mainly during bouts of highly tortuous and area restricted movements (ARM). Bats switched from straight flight to ARM after encountering conspecifics. In the forested landscape, common noctules hunted both during ARM and during straight flights. The onset of ARM did not correlate with the presence of conspecifics. Common noctules showed a lower feeding rate and encountered more conspecifics above the forested than above the cropland dominated landscape. We conjecture that prey distribution above cropland was patchy and unpredictable, thus making eavesdropping on hunting conspecifics crucial for bats during search for prey patches. In contrast, small scale structural diversity of the forested landscape possibly led to a more homogeneous prey distribution at the landscape scale, thus enabling bats to find sufficient food independent of conspecific presence. This suggests that predators depending on ephemeral prey can increase their foraging success in structurally poor landscapes by using social information provided by conspecifics. Hence, a minimum population density might be obligatory to enable successful foraging in simplified landscapes.     

The cost of migratory prey: seasonal changes in semi‐domestic reindeer distribution influences breeding success of Eurasian lynx in northern Norway

Migratory prey is a widespread phenomenon that has implications for predator–prey interactions. By creating large temporal variation in resource availability between seasons it becomes challenging for carnivores to secure a regular year‐round supply of food. Some predators may respond by following their migratory prey, however, most predators are sedentary and experience strong seasonal variation in resource availability. Increased predation on alternative prey may dampen such seasonal resource fluctuations, but reduced reproduction rates in predators is a predicted consequence of migratory primary prey behavior that has received little empirical attention. We used data from 23 GPS collared Eurasian lynx Lynx lynx monitored during 2007–2013 in northern Norway, to examine how spatio‐temporal variation in the migratory behavior of semi‐domestic reindeer Rangifer tarandus influences lynx spatial organization and reproductive success using estimates of seasonal home range overlap and breeding success. We found that lynx of both sexes maintained seasonally stable home ranges and exhibited site fidelity across years, independent of whether they had access to reindeer throughout the year or experienced a scarcity of reindeer in winter due to migration. However, lynx without access to reindeer in winter showed a decreased probability of reproducing and a tendency for lowered kitten survival into their first winter, when compared to female lynx with reindeer available year around. This supports the hypothesis that sedentary predators experience demographic costs in systems with migratory primary prey. Changes in the migratory behavior of ungulates, including disrupted migrations, is therefore likely to have bottom–up effects on the population dynamics of sedentary predators as well as the previously documented consequences for ungulate population dynamics.     

Jaguar and Puma Activity Patterns and Predator‐Prey Interactions in Four Brazilian Biomes

Jaguars (Panthera onca) and pumas (Puma concolor) coexist throughout the Neotropics. Using camera trapping in four Brazilian biomes, we compare the daily activity patterns of the jaguar and puma, and their relationships with their main prey species. We used a kernel density method to quantify daily activity patterns and to investigate overlap between these predators and their main prey. Both cats showed intensive nocturnal and crepuscular activity (0.69 and 0.14 kernel density, respectively, for jaguars; 0.68 and 0.19 kernel density, respectively, for pumas). Only in the Pantanal did we observe a pattern of concentrated diurnal activity for both species. We found little temporal segregation between jaguars and pumas, as they showed similar activity patterns with high coefficients of overlapping (average ?₁ = 0.86; SE = 0.15). We also observed a significant overlap between the activity patterns of the predators and their main prey species, suggesting that both predators adjust their activity to reduce their foraging energy expenditure. Our findings suggest that temporal partitioning is probably not a generalized mechanism of coexistence between jaguars and pumas; instead, the partitioning of habitat/space use and food resources may play a larger role in mediating top predator coexistence. Knowledge about these behavior aspects is crucial to elucidating the factors that enable coexistence of jaguars and pumas. Furthermore, an understanding of their respective activity periods is relevant to management and associated research efforts.     

Is larger better in sit-and-wait predators? Competitive superiority in Hydra

Contrary to a generalisation arising from many studies, a larger body size is not always the key to competitive superiority amongst animals. An analysis of competition between pairs of Hydra oligactis, Hydra vulgaris and Hydra circumcincta, that simultaneously encountered a single prey item, showed that competitive success in these sessile predators depended on species and clone in inter- and intraspecific competition, respectively. H. oligactis appeared to be competitively superior, even to the larger H. vulgaris individuals. Phenotypic traits important for prey capture, such as the fraction of the nematocyst that penetrates the prey (penetrants), were positively related to success in intraspecific competition. Body size appeared to be a positive key factor in determining foraging success in the competition between pairs of conspecifics from single or different clones. In contrast to the results of the intraspecific competition, body size was not significantly related to the foraging success of competing heterospecifics.     

The influence of diet on foraging habitat models: a case study using nursing Antarctic fur seals

Predictable sources of food underpin lifetime reproductive output in long lived animals. The most important foraging areas of top marine predators are therefore likely to be related to environmental features that enhance productivity in predictable spatial and temporal patterns. Even so, although productive areas within the marine environment are distributed patchily in space and time, most studies assess the relationships between feeding activity and proximate, not long term, environmental characteristics. In addition, individuals within a population may exploit different prey types, and these are often associated with different hydrographic features. Until now, models attempting to associate core foraging areas (CFAs) of marine predators with the environmental characteristics of those areas have not considered the diet of individual animals, despite the influence this could have on these relationships. We used bathymetry and multi‐year (n=24) mean sea surface temperature and variability as predictors of CFAs of lactating Antarctic fur seals Arctocephalus gazella at Heard Island. The effect of prey types on the predictability of these models was explored by matching diet and foraging trip data of individual seals (n=40 seals, n=1 trip each). Differences in diet between seals were mirrored by their spatial behaviour. Foraging strategies differed both between and within groups of seals consuming different diets. Long‐term environmental parameters were useful for predicting the foraging activity of seals that consumed a single prey type with relatively specific habitat preferences, but not for those that consumed single or multiple prey types associated with more varied habitats. Ignoring individual variation in predator diet probably contributes to the poor performance of foraging habitat models. These findings highlight the importance of incorporating individual specialization in foraging behaviour into ecological models and management of predator populations.     

Use of prey hotspots by an avian predator: purposeful unpredictability?

The use of space by predators in relation to their prey is a poorly understood aspect of predator-prey interactions. Classic theory suggests that predators should focus their efforts on areas of abundant prey, that is, prey hotspots, whereas game-theoretical models of predator and prey movement suggest that the distribution of predators should match that of their prey's resources. If, however, prey are spatially anchored to one location and these prey have particularly strong antipredator responses that make them difficult to capture with frequent attacks, then predators may be forced to adopt alternative movement strategies to hunt behaviorally responsive prey. We examined the movement patterns of bird-eating sharp-shinned hawks (Accipiter striatus) in an attempt to shed light on hotspot use by predators. Our results suggest that these hawks do not focus on prey hotspots such as bird feeders but instead maintain much spatial and temporal unpredictability in their movements. Hawks seldom revisited the same area, and the few frequently used areas were revisited in a manner consistent with unpredictable returns, giving prey little additional information about risk.     

Web-building management in an orb-weaving spider, Zygiella x-notata: influence of prey and conspecifics

According to optimal foraging theory, spiders should adapt their web building to environmental variations. Until now, there was no data on the influence of simultaneous information coming from different environmental factors on web building behaviour. Under laboratory conditions, we studied the behaviour of Zygiella x-notata in the presence of prey, conspecifics, or both simultaneously. There was a stimulating effect of prey, but web building was not affected by the presence of conspecifics. When spiders and prey were present simultaneously, the effect was similar to that of prey alone; it seemed that there was no interactive influence of both factors. We discussed about the use of environmental information by spiders in foraging behaviour.     

Top carnivores increase their kill rates on prey as a response to human-induced fear

The fear induced by predators on their prey is well known to cause behavioural adjustments by prey that can ripple through food webs. Little is known, however, about the analogous impacts of humans as perceived top predators on the foraging behaviour of carnivores. Here, we investigate the influence of human-induced fear on puma foraging behaviour using location and prey consumption data from 30 tagged individuals living along a gradient of human development. We observed strong behavioural responses by female pumas to human development, whereby their fidelity to kill sites and overall consumption time of prey declined with increasing housing density by 36 and 42%, respectively. Females responded to this decline in prey consumption time by increasing the number of deer they killed in high housing density areas by 36% over what they killed in areas with little residential development. The loss of food from declines in prey consumption time paired with increases in energetic costs associated with killing more prey may have consequences for puma populations, particularly with regard to reproductive success. In addition, greater carcass availability is likely to alter community dynamics by augmenting food resources for scavengers. In light of the extensive and growing impact of habitat modification, our study emphasizes that knowledge of the indirect effects of human activity on animal behaviour is a necessary component in understanding anthropogenic impacts on community dynamics and food web function.     

Mallards Feed Longer to Maintain Intake Rate under Competition on a Natural Food Distribution

Animals foraging in groups may benefit from a faster detection of food and predators, but competition by conspecifics may reduce intake rate. Competition may also alter the foraging behaviour of individuals, which can be influenced by dominance status and the way food is distributed over the environment. Many studies measuring the effects of competition and dominance status have been conducted on a uniform or highly clumped food distribution, while in reality prey distributions are often in‐between these two extremes. The few studies that used a more natural food distribution only detected subtle effects of interference and dominance. We therefore conducted an experiment on a natural food distribution with focal mallards Anas platyrhynchos foraging alone and in a group of three, having a dominant, intermediate or subordinate dominance status. In this way, the foraging behaviour of the same individual in different treatments could be compared, and the effect of dominance was tested independently of individual identity. The experiment was balanced using a 4 × 4 Latin square design, with four focal and six non‐focal birds. Individuals in a group achieved a similar intake rate (i.e. number of consumed seeds divided by trial length) as when foraging alone, because of an increase in the proportion of time feeding (albeit not significant for subordinate birds). Patch residence time and the number of different patches visited did not differ when birds were foraging alone or in a group. Besides some agonistic interactions, no differences in foraging behaviour between dominant, intermediate and subordinate birds were measured in group trials. Possibly group‐foraging birds increased their feeding time because there was less need for vigilance or because they increased foraging intensity to compensate for competition. This study underlines that a higher competitor density does not necessarily lead to a lower intake rate, irrespective of dominance status.     

Responses to competition effects of two anuran tadpoles according to life-history traits

Experimental manipulations of the densities of two larval anurans, Pelodytes punctatus and Bufo bufo , showed that these species compete asymmetrically in semi-natural conditions. Growth, mass at metamorphosis, date of metamorphosis, and survival were used as measures of response to interspecific competition. A mechanistic approach was used to collect information on the behaviour of the two species in different conditions. The competitive superiority of Pelodytes at individual level was correlated with a larger body, faster growth rate, increased per capita competitive impact on conspecifics, and greater reduction in the availability of trophic and spatial resources. In the presence of Pelodytes, Bufo showed slower growth, smaller size at metamorphosis and reduced survival. In the interspecific treatments Bufo individuals modified their behaviour by increasing activity and use of the water column while Pelodytes did not change their foraging activity or space use in the aquaria. However, the presence of Bufo resulted in a reduced larval period and smaller size at metamorphosis. We hypothesise that the presence of Bufo act as a signal of environmental degradation and shorten the larval period of Pelodytes, a typical temporal pond breeder . The smaller Bufo tadpoles are potentially stronger competitors at population level because they use relatively large amounts of energy (greater densities and higher metabolic rates). Consequently, they use larger proportions of the shared resources than their larger competitor. A possible evolutionary response for larger tadpoles is the development of interference mechanisms or "escaping" from ephemeral ponds where mortality by drying represent a high risk.     

The dietary basis for temporal partitioning: food habits of coexisting Acomys species

Two rodent species of the genus Acomys coexist on rocky terrain in the southern deserts of Israel. The common spiny mouse (A. cahirinus) is nocturnally active whereas the golden spiny mouse (A. russatus) is diurnally active. An early removal study suggested that competition accounts for this pattern of temporal partitioning: the golden spiny mouse is forced into diurnal activity by its congener. Theoretically, temporal segregation should facilitate coexistence if the shared limiting resources differ at different times (primarily among predators whose prey populations have activity rhythms), or if they are renewed within the period of the temporal segregation. We studied food preferences of the two Acomys species in a controlled cafeteria experiment in order to assess resource overlap and the potential for competition for food between the two species. We found no significant difference in food preferences between species. The dietary items preferred by both were arthropods. We also carried out a seasonal study of the percentage and identity of arthropods taken in the field by individuals of the two species. Individuals of both species took on annual average a high percentage of arthropods in their diets. Seasonal diet shifts reflect seasonal abundance of arthropods at Ein Gedi during day and night. Diurnal activity may also reduce interspecific interference competition between A. russatus and A. cahirinus. However, the strong interspecific dietary overlap in food preference, the heavy reliance on arthropods in spiny mouse diets, and the seasonal and circadian differences in arthropod consumption suggest that prey partitioning may be a viable mechanism of coexistence in this system. Received: 6 July 1998 / Accepted: 10 May 1999     

Segregation in space and time explains the coexistence of two sympatric sub‐Antarctic petrels

Biological communities are shaped by competition between and within species. Competition is often reduced by inter‐ and intraspecific specialization on resources, such as differencet foraging areas or time, allowing similar species to coexist and potentially contributing to reproductive isolation. Here, we examine the simultaneous role of temporal and spatial foraging segregation within and between two sympatric sister species of seabirds, Northern Macronectes halli and Southern Macronectes giganteus Giant Petrels. These species show marked sexual size dimorphism and allochrony (with earlier breeding by Northern Giant Petrels) but this is the first study to test for differences in foraging behaviours and areas across the entire breeding season both between the two species and between the sexes. We tracked males and females of both species in all breeding stages at Bird Island, South Georgia, to test how foraging distribution, behaviour and habitat use vary between and within species in biological time (incubation, brood‐guard or post‐brood stages) and in absolute time (calendar date). Within each breeding stage, both species took trips of comparable duration to similar areas, but due to breeding allochrony they segregated temporally. Northern Giant Petrels had a somewhat smaller foraging range than Southern Giant Petrels, reflecting their greater exploitation of local carrion and probably contributing to their recent higher population growth. Within species, segregation was spatial, with females generally taking longer, more pelagic trips than males, although both sexes of both species showed unexpectedly plastic foraging behaviour. There was little evidence of interspecific differences in habitat use. Thus, in giant petrels, temporal segregation reduces interspecific competition and sexual segregation reduces intraspecific competition. These results demonstrate how both specialization and dynamic changes in foraging strategies at different scales underpin resource division within a community.     

Predation risk in tadpole populations shapes behavioural responses of prey but not strength of trait‐mediated indirect interactions

Prey animals often respond to predators by reducing activity levels. This can produce a trait‐mediated indirect interaction (TMII) between predators and prey resources, whereby reduced foraging by prey in the presence of a predator causes an increase in prey resources. TMIIs play important roles in structuring communities, and it is important to understand factors that determine their strength. One such influence may be behavioural variation in the prey species, with indirect effects of predators being stronger within populations that are more responsive to the presence of a predator. We tested 1) whether the behavioural responsiveness of populations of wood frog tadpoles to predator cues was related to the predation risk in their native ponds, and 2) whether more responsive tadpoles yielded stronger TMIIs. To do this, we 1) measured the activity of tadpoles from 18 populations in mesocosms with and without caged predators, and 2) measured changes in the biomass of periphyton (the tadpoles’ diet) between predator treatments for each population. We found that tadpoles from higher predation risk ponds reduced their time outside refuges more in the presence of predators and tended to move less when visible, suggesting possible local adaptation to predation regimes. Though the presence of predators generally resulted in higher periphyton biomass – a TMII – there was no evidence that the strength of this TMII was affected by variation in tadpole behaviour. Foraging activity and general activity may be decoupled to some extent, enabling high predation risk‐adapted tadpoles to limit the fitness costs of reduced foraging when predators are present.     

Food-related bray calls in wild bottlenose dolphins (Tursiops truncatus)

Because cetaceans are difficult to study in the wild, little is known about how they use their sounds in their natural environment. Only the recent development of passive acoustic localization systems has enabled observations of the communication behaviour of individuals for correlation with their surface behaviour. Using such a system, I show that bottlenose dolphins in the Moray Firth, Scotland, produce low-frequency bray calls which are clearly correlated with feeding on salmonids. The production of these calls is followed by fast approaches by conspecifics in the area. In animals which use sound as a foraging tool, it is difficult to distinguish between food calls which have evolved because of their role in attracting conspecifics, and food manipulation or searching calls which may attract conspecifics as a by-product. However, the low-frequency structure of the bottlenose dolphin bray suggests that it evolved because of a role in manipulating prey rather than in attracting conspecifics. This conclusion suggests that dolphins exploit the perceptual systems of their prey to facilitate capture.     

Environmental heterogeneity amplifies behavioural response to a temporal cycle

Resource acquisition is integral to maximise fitness, however in many ecosystems this requires adaptation to resource abundance and distributions that seldom stay constant. For predators, prey availability can vary at fine spatial and temporal scales as a result of changes in the physical environment, and therefore selection should favour individuals that can adapt their foraging behaviour accordingly. The tidal cycle is a short, yet predictable, temporal cycle, which can influence prey availability at temporal scales relevant to movement decisions. Here, we ask whether black‐legged kittiwakes Rissa tridactyla can adjust their foraging habitat selection according to the tidal cycle using GPS tracking studies at three sites of differing environmental heterogeneity. We used a hidden Markov model to classify kittiwake behaviour, and analysed habitat selection during foraging. As expected for a central‐place forager, we found that kittiwakes preferred to forage nearer to the breeding colony. However, we also show that habitat selection changed over the 12.4‐h tidal cycle, most likely because of changes in resource availability. Furthermore, we observed that environmental heterogeneity was associated with amplified changes in kittiwake habitat selection over the tidal cycle, potentially because environmental heterogeneity drives greater resource variation. Both predictable cycles and environmental heterogeneity are ubiquitous. Our results therefore suggest that, together, predictable cycles and environmental heterogeneity may shape predator behaviour across ecosystems.     

Responses of larval dragonflies to conspecific and heterospecific predator cues

Abstract.  1. In cannibalistic populations, smaller individuals are subject to predation by larger conspecifics, and small individuals commonly alter their behaviour in response to cannibals. Little is known, however, about the underlying cues that trigger such responses and how the behavioural responses to conspecific cannibals differ from heterospecific predators.
2. This study tests which cues are used for the detection of conspecific predators in the larva of the dragonfly Plathemis lydia and how the behavioural response to cannibals differed from the response to heterospecific predators.
3. Individuals were exposed to chemical cues, visual cues, and a combination of both cues from conspecifics as well as no predator and heterospecific predator controls during which their activity and feeding rates were observed.
4. Individuals increased their activity, spatial movement and feeding behaviour in response to either visual or chemical cues from conspecific predators, which was opposite to responses displayed with cues from heterospecific predators. Interestingly, the responses to visual and chemical cues from conspecifics combined were weaker than to either cue in isolation and similar to the no cue control.
5. The results clearly indicate that individuals are able to use chemical and visual cues to detect even very subtle differences in phenotype of conspecific predators.
6. The opposite response in behaviour when exposed to conspecific cannibals vs. heterospecific predators suggests that the presence of cannibals will increase the mortality risk of small individuals due to heterospecific predation. This risk-enhancement is likely to have important consequences for the dynamics of predator–prey interactions.     

Foraging behavior of an estuarine predator, the blue crab Callinectes sapidus in a patchy environment

To define general principles of predator‐prey dynamics in an estuarine subtidal environment, we manipulated predator density (the blue crab, Callinectes sapidus) and prey (the clam, Macoma balthica) patch distribution in large field enclosures in the Rhode River subestuary of the central Chesapeake Bay. The primary objectives were to determine whether predators forage in a way that maximizes prey consumption and to assess how their foraging success is affected by density of conspecifics. We developed a novel ultrasonic telemetry system to observe behavior of individual predators with unprecedented detail. Behavior of predators was more indicative of optimal than of opportunistic foraging. Predators appeared responsive to the overall quality of prey in their habitat. Rather than remaining on a prey patch until depletion, predators appeared to vary their patch use with quality of the surrounding environment. When multiple (two) prey patches were available, residence time of predators on a prey patch was shorter than when only a single prey patch was available. Predators seemed to move among the prey patches fairly regularly, dividing their foraging time between the patches and consuming prey from each of them at a similar rate. That predators more than doubled their consumption of prey when we doubled the number of prey (by adding the second patch) is consistent with optimizing behaviors ‐ rather than with an opportunistic increase in prey consumption brought about simply by the addition of more prey. Predators at high density, however, appeared to interfere with each other's foraging success, reflected by their lower rates of prey consumption. Blue crabs appear to forage more successfully (and their prey to experience higher mortality) in prey patches located within 15–20 meters of neighboring patch, than in isolated patches. Our results are likely to apply, at least qualitatively, to other crustacean‐bivalve interactions, including those of commercial interest; their quantitative applicability will depend on the mobility of other predators and the scale of patchiness they perceive.     

Prey switching as a means of enhancing persistence in predators at the trailing southern edge

Understanding the effects of climate change on species’ persistence is a major research interest; however, most studies have focused on responses at the northern or expanding range edge. There is a pressing need to explain how species can persist at their southern range when changing biotic interactions will influence species occurrence. For predators, variation in distribution of primary prey owing to climate change will lead to mismatched distribution and local extinction, unless their diet is altered to more extensively include alternate prey. We assessed whether addition of prey information in climate projections restricted projected habitat of a specialist predator, Canada lynx (Lynx canadensis), and if switching from their primary prey (snowshoe hare; Lepus americanus) to an alternate prey (red squirrel; Tamiasciurus hudsonicus) mitigates range restriction along the southern range edge. Our models projected distributions of each species to 2050 and 2080 to then refine predictions for southern lynx on the basis of varying combinations of prey availability. We found that models that incorporated information on prey substantially reduced the total predicted southern range of lynx in both 2050 and 2080. However, models that emphasized red squirrel as the primary species had 7–24% lower southern range loss than the corresponding snowshoe hare model. These results illustrate that (i) persistence at the southern range may require species to exploit higher portions of alternate food; (ii) selection may act on marginal populations to accommodate phenotypic changes that will allow increased use of alternate resources; and (iii) climate projections based solely on abiotic data can underestimate the severity of future range restriction. In the case of Canada lynx, our results indicate that the southern range likely will be characterized by locally varying levels of mismatch with prey such that the extent of range recession or local adaptation may appear as a geographical mosaic.     

Foraging behaviour by an intraguild predator blowfly, <Emphasis Type="Italic">Chrysomya albiceps</Emphasis> (Diptera: Calliphoridae)

Optimal foraging theory assumes that predators use different prey types to maximize their rate of energetic gain. Studies focusing on prey preference are important sources of information to understand the foraging dynamics of Chrysomya albiceps. The purpose of this investigation is to determine the influence of larval starvation in C. albiceps on the predation rate of different prey blowfly species and instars under laboratory conditions. Our results suggest that C. albiceps prefers Cochliomyia macellaria larvae to Chrysomya megacephala under non-starvation and starvation conditions. Nevertheless, predators gained more weight consuming C. macellaria. This result suggests that C. albiceps profit more in consuming C. macellaria rather than C. megacephala. The foraging behaviour displayed by C. abiceps on their prey and the consequences for the blowfly community are also discussed.